IMS TRAINING MATERIAL

1. COMPONENTS.......................................................................................................................................................3
1.1 IMS/VS.................................................................................................................................................................3
1.2 IMS/360................................................................................................................................................................3
1.3 DL/I - DOS/VS.....................................................................................................................................................3
1.4 FIVE COMPONENTS OF IMS ENVIRONMENT...................................................................................................................3
2. DL/I TERMINOLOGY............................................................................................................................................6
2.1 HIERARCHICAL STRUCTURE FOR HOSPITAL DATABASE.......................................................................7
3. DATABASE HIERARCHY CHART......................................................................................................................8
3.1 SEGMENT (TYPE)..............................................................................................................................................8
3.2 SEGMENT (OCCURRENCES)...........................................................................................................................8
3.3 SEGMENT (RELATIONSHIPS)..........................................................................................................................9
3.4 SEGMENT (TWINS) - MULTIPLE OCCURRENCE......................................................................................................9
3.5 HIERARCHICAL PATHS....................................................................................................................................9
3.6 DATABASE (IMS)...............................................................................................................................................9
3.7 DATABASE RECORD.......................................................................................................................................10
4. DESIGNING AND DESCRIBING THE DATABASE TO IMS / DL - I............................................................11
4.1 KEY OR SEQUENCED FIELDS.......................................................................................................................11
4.2 ADDITIONAL SEARCH FIELDS.....................................................................................................................11
4.3 DATABASE DESCRIPTION (DBD).................................................................................................................12
4.4 HOSPITAL DATABASE DBDGEN MACROS..................................................................................................................13
5. APPLICATION / LOGICAL DATA-STRUCTURE (PSB).................................................................................15
5.1 HOSPITAL DATABASE PSBGEN MACROS...................................................................................................................16
6. DL / I PROGRAMMING CONSIDERATIONS..................................................................................................18
6.1 WORKING STORAGE SECTION....................................................................................................................18
6.2 LINKAGE SECTION.........................................................................................................................................19
6.3 PROCEDURE DIVISION..................................................................................................................................19
6.4 DL/I CALLS.......................................................................................................................................................20
6.5 SEGMENT SEARCH ARGUMENT: - ..............................................................................................................................22
6.6 SSA STRUCTURE: ...........................................................................................................................................23
6.7 SSA TYPES: ......................................................................................................................................................24
6.8 CALL TYPES.....................................................................................................................................................25
6.9 DATABASE DL/I CALLS..................................................................................................................................26
6.10 RELATIONAL OPERATORS..........................................................................................................................27
6.11 HOSPITAL DATABASE SEGMENT OCCURRENCE CHART....................................................................28
6.12 RANDOM RETRIEVAL USING GU CALL...................................................................................................29
6.13 SEQUENTIAL RETRIEVAL USING GN CALL............................................................................................29
6.14 GN CALLS WITHOUT SSA'S (UNQUALIFIED GN CALLS)..............................................................................................31
6.15 GN CALL WITH UNQUALIFIED SSA'S (QUALIFIED GN CALL).....................................................................................31
6.16 GN CALL WITH QUALIFIED SSA'S (QUALIFIED GN CALL)........................................................................................31
6.17 GN CALLS - STATUS CODES...........................................................................................................................32
6.18 SEQUENTIAL RETRIEVAL USING GNP CALL..........................................................................................33
6.19 GNP CALLS WITHOUT SSA'S (UNQUALIFIED GNP CALL)..........................................................................................33
6.20 GNP CALL WITH UNQUALIFIED SSA'S (QUALIFIED GNP CALL).................................................................................34
6.21 GNP CALL WITH QUALIFIED SSA'S (QUALIFIED GNP CALL).....................................................................................35
6.22 GNP CALLS - STATUS CODE...........................................................................................................................35
7. UPDATING AND DELETING SEGMENTS.......................................................................................................36
7.1 GET HOLD CALLS...........................................................................................................................................36
7.2 DELETE AND REPLACE RULES....................................................................................................................36

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IMS TRAINING MATERIAL

7.3 REPLACING SEGMENTS IN THE DATABASE USING THE REPL FORM................................................37

7.4 REPL CALL - STATUS CODE..........................................................................................................................37
7.5 DELETING SEGMENTS IN THE DATABASE USING THE DLET FUNCTION.........................................38
7.6 DLET CALL - STATUS CODES.......................................................................................................................38
8. INSERTING SEGMENTS INTO AN EXISTING DATABASE.........................................................................39

9. DBD INSERT RULES............................................................................................................................................40

9.1 ISRT CALL (INSERT MODE) - STATUS CODE.............................................................................................40
9.2 LOADING SEGMENTS INTO AN EMPTY OR SCRATCH DATABASE......................................................41
9.3 ISRT CALL (LOAD MODE) - STATUS CODES..............................................................................................41
10. ADVANCED DATABASE PROCESSING........................................................................................................42
10.1 BOOLEAN SSA STATEMENTS.....................................................................................................................42
10.2 SSA'S USING COMMAND CODES...............................................................................................................43
10.3 F COMMAND CODE......................................................................................................................................44
10.4 L COMAMND CODE......................................................................................................................................45
10.5 D COMMAND CODE & N COMMAND CODE...........................................................................................46
10.6 RETRIEVING AND REPLACING WITHOUT COMMAND CODE............................................................47
10.7 C COMMAND CODE......................................................................................................................................47
10.8 Q COMMAND CODE......................................................................................................................................48
10.9 U AND V COMMAND CODES......................................................................................................................48
10.10 P COMMAND CODE...................................................................................................................................49
10.11 NULL COMMAND CODE...........................................................................................................................50
10.12 MULTIPLE POSITIONING WITHIN THE PCB..........................................................................................51
10.13 MULTIPLE PCB'S IN A PSB.........................................................................................................................55
10.14 LOGICAL DATABASES...............................................................................................................................56
10.15 LOGICAL RELATIONSHIPS.......................................................................................................................57
10.16 DBDGEN'S FOR PHYSICAL DATABASE WITH LOGICAL RELATIONSHIPS....................................59
10.17 PSBGEN USING LOGICAL DATABASE...................................................................................................59
10.18 IMS SYSTEM DATASETS...........................................................................................................................60
11. APPENDIX - A......................................................................................................................................................61
11.1 PROCESSING OPTIONS - PROCOPT =....................................................................................................................61
12. APPENDIX - B......................................................................................................................................................62
12.1 DL/I STATUS CODES.....................................................................................................................................62
13. APPENDIX - C......................................................................................................................................................63
13.1 SYSTEM SERVICE - DL/I CALLS.................................................................................................................63
13.2 CHECKPOINT(CHKP) CALL.........................................................................................................................63
13.3 BASIC CHECKPOINT CALL.........................................................................................................................63
13.4 SYMBOLIC CHECKPOINT CALL................................................................................................................64
13.5 RESTART CALL (XRST)................................................................................................................................65
13.6 ROLLBACK CALLS (ROLL AND ROLB)....................................................................................................66

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IMS TRAINING MATERIAL

1. Components
1.1 IMS/VS
- This is the latest version
- Consists of a DL/I component that interface with the Database
- Consists of Data communication component that interface with the users at remote
terminals
- Runs under operating system MVS/OS/VS1/OS/VS2

1.2 IMS/360
- Runs under operating system OS/VS1/OS/VS2
- Consists of a DL/I component that interface with the Database
- Consists of a Data Communication component that interface with the users at remote
terminals

1.3 DL/I - DOS/VS

- Runs under operating system DOS/VSE
- Consists only of interface with the database

1.4 Five Components of IMS Environment

A) Database Management System

- This is the heart of IMS subsystem

- Shared by many concurrent tasks
- Data is stored in DASD
- Application Programs access data by making DL/I calls

B) DL/I (Data Language / I )

- Is a set of program modules interfacing database and application program

- The modules use standard operating system access methods and a set of specialized
access methods to handle data transfers to and from the database
- This is an Interface Language used by the Application Program

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IMS TRAINING MATERIAL

C) DL/I Control Blocks

- There are two main DL/I control blocks, one describing the database structure, the
other identifying how the database may be accessed by the program
- They are Database Descriptor (DBD), and Program Communication Block (PCB)
- The Database Administration Group normally maintains these control blocks.
- DBD describes the physical structure of a database as well as the way in which it is
stored on the DASD and the way it is accessed
- PSB describes the Logical Structure of a Database as a particular application program
views it. It identifies which pieces of data a program is allowed to access and the
kinds of functions (operations) it can perform on each collection of data.

D) Application Program

- These are designed and coded by the programmers

- The programs use a standard DL/I interface to other IMS components
- DL/I Application Programs use standard CALL statements with a parameter list to
communicate with IMS.
- Programs may be written in COBOL, PL/I. ASM

E) Data Communication
- Is a set of program modules that allow the program to communicate with remote
terminals
- Programs communicate with terminals through a Standard Interface Language using
CALL statements with a parameter list.

Operating
System
IMS Database

DL/I

IMS IMS Data Remote

Control Communication Terminals
Blocks

Figure 1 Application
Program

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IMS TRAINING MATERIAL

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 2. DL/I Terminology
Assume, the general information we store in the HOSPITAL Database is:

I] HOSPITAL information
A] WARDS & ROOMS information in each hospital
1) PATIENTS information in each WARD
a) SYMPTOMS
b) TREATMENTS
c) DOCTORS
B] SPECIAL FACILITIES information in each hospital

COBOL structure for Hospital Database is: -

1 HOSPITAL
05 HOSPNAME PIC X(20) Unique Key
05 Hosp-Address PIC X(30)
05 Hosp-Phone PIC X(10)
1 WARD
05 WARDNO PIC X(2) Unique Key
05 Total-Rooms PIC X(3)
05 Total-Beds PIC X(3)
05 BEDAVAIL PIC X(3) Search
05 WARDTYPE PIC X(20) Search
1 PATIENT
05 PATNAME PIC X(20) Search
05 Patient-Address PIC X(30)
05 Patient-Phone PIC X(10)
05 BEDIDENT PIC X(4) Unique Key
05 DATEADMT PIC X(6) Search
1 SYMPTOM
05 DIAGNOSE PIC X(20) Search
05 SYMPDATE PIC X(6) Non-Unique Key
05 Treat-Description PIC X(20)
05 Symp-Doctor PIC X(20)
05 Symp-Doc-Phone PIC X(10)
1 TREATMNT
05 TRTYPE PIC X(20) Search
05 TRDATE PIC X(6) Non-Unique Key
05 Medicine-Type PIC X(20)
05 Diet-Comment PIC X(30)
05 Surgery-Flag PIC X
05 Surgery-Date PIC X(6)
05 Surgery-Comment PIC X(30)
 1 DOCTOR
05 DOCTNAME PIC X(20) Search
05 Doct-Address PIC X(30)
05 Doct-Phone PIC X(10)
05 SPECIALT PIC X(20) Search
1 FACILITY
05 FACTYPE PIC X(20) Search
05 Tot-Facility PIC X(3)
05 FACAVAIL PIC X(3) Search

2.1 HIERARCHICAL STRUCTURE FOR

HOSPITAL DATABASE

LEVEL 1 (ROOT) HOSPITAL

LEVEL 2 WARD FACILITY

PATIENT
LEVEL 3

SYMPTOM TREATMENT DOCTOR

LEVEL 4

Figure 2 The above chart shows 7 segment types in 4 levels

− Note
–IMS maintains an Inverted Tree Structure starting with the Root Segment by ensuring that no
segment has more than one parent
–Each box represents a segment name of up to 8 characters at each level called as a Segment
Type
–The above diagram of Hospital Database is called as an Database Hierarchy Chart
–The Hierarchy can go up to fifteen levels down
–The Hierarchy can represent up to 255 segment types
 3. DATABASE HIERARCHY CHART
3.1 SEGMENT (TYPE)
- It is the smallest unit of information DL/I handles
- Within each segment are one or more data fields
- Each 01 level data name defines one of the segments in the Hospital Database
- Each 03 level data name defines one of the fields within a segment
- If an application program requires information only about a segment, it does not even
have to know that the other segments exists, or what their relationships are within the
database
- Also known as a Segment Type
- Can have up to 255 segment types in a Database record, and up to 15 segment types
in any one hierarchical path.

3.2 SEGMENT (OCCURRENCES)

B C
A
HOSPITAL

WARD FACILITY

3
2
1
PATIENT

SYMPTOM TREATMENT DOCTOR

Figure 3 :- Can store as many segment occurrences as the storage permits for any segment type.
3.3 SEGMENT (RELATIONSHIPS)
- The terms Parent and child are used to describe the relationships between segment
types within a database
- A segment that has one or more segments directly below it in the hierarchy is called a
PARENT segment
- A segment that has a segment directly above it in the hierarchy is called a CHILD
segment
- Parent and Child segments are relative terms which depends upon which portion of
the database hierarchy is under focus of discussion
- A child segment is also called as a DEPENDENT segment
- The concept of Dependent segments extends more than one level in the hierarchy
- If a parent occurrence is deleted, so are all its children

3.4 SEGMENT (TWINS) - Multiple Occurrence

- All occurrences of a particular segment type under a single parent segment
occurrence are called TWINS
- The set of all Twins dependent on a particular parent is often referred to as a TWIN
CHAIN
- For example :- All the symptom occurrences for a particular patient are called TWINS
in a TWIN CHAIN

3.5 HIERARCHICAL PATHS

- Segments are always accessed and retrieved along the Hierarchical Paths
- A path is a route line that Begins at the Root segment, travels through the segments at
Intermediate levels in the hierarchy and Ends at a segment in the Bottom of the
hierarchy
- There are Four paths in the Hospital Database such as
HOPSITAL HOSPITAL HOSPITAL HOSPITAL
WARD WARD WARD FACILITY
PATIENT PATIENT PATIENT
SYMPTOM TREATMENTDOCTOR

3.6 DATABASE (IMS)

- A database consists of all the Root Segment occurrences along with their dependants
- Is normally shared by Multiple Applications
3.7 DATABASE RECORD
- A database record consists of a SINGLE occurrence of the ROOT segment and all of
its dependent segments
- In the hospital database, a single record consist of a single occurrence of the
HOSPITAL segment and all of the segment occurrences below it that belong to a
particular hospital in the hierarchy
4. DESIGNING AND DESCRIBING THE
DATABASE TO IMS / DL - I
- A number of factors must be considered by DBA while designing the database
- Questions about database design, that a programmer is concerned with are
- Segment names a program may access
- Various fields formats within the accessed segments
- Names and formats of the fields used for search
- Hierarchical relationships of the accessed segments
- Processing permissions on the accessed segments
- A segment may not have any search or key fields defined on it.

4.1 KEY OR SEQUENCED FIELDS

- The Database Designer has to decide not only the contents in each segment, but also
what content with each segment would be known to IMS as key fields and search
fields
- A key or sequenced field is a field with the segment that DL/I uses to maintain
segments in the Ascending Sequence
- Only a single field within each segment may be designated as a key or sequence field
- Key field in a segment is OPTIONAL
- Key field may be designated as UNIQUE or NON-UNIQUE
- A ROOT segment is required to have a UNIQUE key field

4.2 ADDITIONAL SEARCH FIELDS

- A field on which the segments are not sequenced, but contents of which can be used
to perform a SEARCH in the database is called as well as designated as a SEARCH
field for a segment
- Up to 255 search fields can be identified in a segment including the KEY field
- Any data item or a combination of contingents data items can be designated as a
search field
4.3 DATABASE DESCRIPTION (DBD)
- Once segments are defined, the Hierarchical Structure decided upon, the key and
search fields identified, DBA can communicate this design of Database to DL/I
- Accordingly a CONTROL BLOCK for Database called DBD is created in a DL/I
library, which describes the physical structure of a database to IMS
- DBD is created by a process called DBD Generation or DBDGEN, wherein DBA
codes a series of Control statements. The process is performed only once for database
unless the physical structure of database undergoes a change.
- DBDGEN control statements are Assembler Language Macros supplied by IBM and
submitted via JCL invoking a catalogued procedure called DBDGEN producing an
OBJECT module.
- Macros are stored in Maclib and load modules are stored in DBDLIB, which is the
DBD itself and ready for loading
- The Hospital database DBD control statements will look like

PRINT NOGEN
DBD NAME=HOSPDBD, ACCESS=HISAM
DATASET DD1=HOPSET, OVFLW=HOSPFLW, DEVICE=3330
SEGM NAME=HOSPITAL, PARENT=0, BYTES=60
FIELD NAME=(HOSPNAME,SEQ,U), BYTES=20, START=1, TYPE=C
SEGM NAME=WARD, PARENT=HOSPITAL, BYTES=31
FIELD NAME=(WARDNO,SEQ,U), BYTES=2, START=1, TYPE=C
FIELD NAME=BEDAVAIL, BYTES=3, START=9, TYPE=C
FIELD NAME=WARDTYPE, BYTES=20, START=12, TYPE=C
SEGM NAME=PATIENT, PARENT=WARD, BYTES=70
FIELD NAME=(BEDIDENT,SEQ,U), BYTES=4, START=61, TYPE=C
FIELD NAME=PATNAME, BYTES=20, START=1, TYPE=C
FIELD NAME=DATEADMT, BYTES=6, START=65, TYPE=C
SEGM NAME=SYMPTOM, PARENT=PATIENT, BYTES=76
FIELD NAME=(SYMPDATE,SEQ), BYTES=6, START=21, TYPE=C
FIELD NAME=DIAGNOSE, BYTES=20, START=1, TYPE=C
SEGM NAME=TREATMNT, PARENT=PATIENT, BYTES=113
FIELD NAME=(TRDATE,SEQ), BYTES=6, START=21, TYPE=C
FIELD NAME=TRTYPE, BYTES=20, START=1, TYPE=C
SEGM NAME=DOCTOR, PARENT=PATIENT, BYTES=80
FIELD NAME=DOCTNAME, BYTES=20, START=1, TYPE=C
FIELD NAME=SPECIALT, BYTES=20, START=61, TYPE=C
SEGM NAME=FACILITY, PARENT=HOSPITAL, BYTES=26
FIELD NAME=FACTYPE, BYTES=20, START=1, TYPE=C
FIELD NAME=FACAVAIL, BYTES=3, START=24, TYPE=C
DBDGEN
FINISH
 END

4.4 Hospital Database DBDGEN macros

PRINT NOGEN - Causes the assembler to suppress the listings of machine
instructions generated by each macro

DBD - Apart from describing the Physical Structure and

Interdependency of segments in Database, it also names the DBD
and the Access method that will be used by DL/I for data
manipulation

DATASET - Specifies the names of files used to store the data. HISAM
database requires two files and their names must be included in the
program execution JCL accessing the database. Device specifies
the device type in which the allocated files will store the segment
data

SEGM - Each SEGM statement names and describes one segment type
that will make up the database. Name operand names the segment
type. Parent operand names the parent of each segment type
thereby defining the Hierarchical Structure of a database. A root
segment is identified by the absence of a Parent operand or
Parent=0. The SEGM statements are coded in the hierarchical
sequence of the segment types, that is, from TOP to BOTTOM and
from LEFT to RIGHT. The Bytes operand specifies the segment
length in terms of bytes.

FIELD - Each field statement names and describes the key and search
fields for a segment. NAME parameter contains from one to three
positional sub-parameters. The first sub-parameter names the key
or search field. If it is the only sub-parameter coded, the field will
be a search field. If SEQ is coded as the second sub-parameter, the
field will be a key field, and the occurrences will be sequenced in
Ascending order. This is optional. If specified, only one key field is
allowed per SEGM statement. If U is coded as the third sub-
parameter, the field is a UNIQUE sequence field unless M is
specified for Multiple value in the field. If neither 'U' nor 'M' is
specified when SEQ is coded, the sequence field is taken to be
unique. A unique sequence field is required for the root segment in
HISAM and HIDAM methods. The START operand tells the
starting byte position of the key or search field relative to the
beginning of the segment. The BYTES operand tells the field
 length in bytes. TYPE operand tells the data type of field,
accordingly C specifies a character field of alphanumeric type, P
specifies a packed Decimal numeric type. C is the default data
type. FIELD statement for the sequence field, if there is one, must
be the first such statement for the segment.
DBDGEN - This statement ends the SEGM and FIELD definitions for the
DBD

FINISH - This statement causes the assembler to set a non-zero condition

code if errors are encountered during the assembly process.

END - This statement marks the end-of-data to the assembler

− Note
That the names of the Segments key & search fields that match in the COBOL Structure with
that of the names used in the DBD is not an IMS requirement.
5. APPLICATION / LOGICAL DATA-
STRUCTURE (PSB)
- Logical Data Structure is a term used to refer to a group of segments that an
application program may access. To the application program, the logical data
structure is the database
- The DBA defines the logical data structure by creating a Control Block called a
Program Specification Block or PSB.
- PSB is created with a process called PSB generation or PSBGEN, very similar to the
DBDGEN process; wherein DBA codes a series of control statements
- PSBGEN control statements are Assembler Language Macros supplied by IBM and
submitted via JCL invoking a catalogue procedure called PSBGEN producing an
OBJECT module.
- Macros are stored in Maclib and Load modules are stored in PSBLIB, which is the
PSB itself and ready for loading
- The PSB control statements for a Retrieved program will look as below.
- Each PSB consists of one or more control blocks called Program Communication
Blocks or PCB's. Each PCB within a PSB defines exactly one Logical Data Structure
- All the PCB's within a single PSB are collectively known as an Application Data
Structure
- It is possible that more than one program may share a single PSB, however, no
program can use more than one PSB in a single execution
- The Logical Data Structures defines all the segments that an application program may
access using that PSB

PCB TYPE=DB, NAME=HOSPDBD, KEYLEN=26

SENSEG NAME=HOSPITAL, PARENT=0, PROCOPT=K
SENSEG NAME=WARD, PARENT=HOSPITAL, PROCOPT=K
SENSEG NAME=PATIENT, PARENT=WARD, PROCOPT=G
PSBGEN LANG=COBOL, PSBNAME=PATRETRV
END
 5.1 Hospital Database PSBGEN macros
PCB - This is the first statement in a PSB. It marks the beginning of one
Program Communication Block (PCB). TYPE operand specifies that this
is a Database PCB as opposed to a terminal PCB. NAME operand names
the DBD for which the PCB is created; KEYLEN specifies the length of
the key feedback area. When the program retrieves a segment using DL/I
GET, IMS not only fetches the requested segment but also places a fully
concatenated key into the key feedback area of PCB mask which consists
of the concatenation of the sequence field values of all the segments in the
hierarchical path from the root down to the retrieved segment

SENSEG - These statements identify the segments in the database that this
application program is sensitive to. NAME operand names a segment that
is sensitive and must be the same as the name coded in the NAME
operand in the SEGM statement in the DBD. PARENT operand names a
segment that is parent to the SENSEG name. This operand identifies the
hierarchical structure of this Logical Data Structure as supported by the
DBD. The PROCOPT operand is optional. It stands for the processing
options and identifies the processing types that may be performed on each
segment by the application program. 'K' means that the segment is key
sensitive only. The application may use the segment only to gain access to
the segments below it in the hierarchy and not to access any data within it.
If a sensitive segment is not key sensitive, it is data sensitive i.e. when
PROCOPT = G, I, R or D or A. Any or all of GIRD may be specified in
any order.

PSBGEN - Identifies the language of the program that will use the PSB and gives a
name to PSB coded at the end.

− Note
1. The sensitive segments must be specified in the hierarchical sequence as in DBD. Such as
Top to Bottom, Left to Right
2. If the PROCOPT operand value is same for all the entries of SENSEG within a PCB then
you may specify PROCOPT operand in the PCB statement itself instead of in each SENSEG.
If PROCOPT operand is specified in both, the SENSEG entry overrides the PCB entry.
However, the PROCOPT = L (Load - to create the initial version of the database) may be
specified only in the PCB statement which cannot be overridden. Also, the PROCOPT = K
(Key sensitivity) may be specified only in the SENSEG statement.
3. For Field Level sensitivity within a sensitive segment include the statement SENDFLD
immediately following the statement SENSEG as
SENDFLD NAME = fieldname, START = position
 SENDFLD NAME = fieldname START = position

Name and the Field Length are inherited from DBD. The order in which field names are
specified is irrelevant
//RETRIEVE EXEC PGM=DFSRRC00, PARM=DLI, PATRETRV
//STEPLIB DD DSN=IMSVS.RESLIB, DISP=SHR
// DD DSN=IMSVS.PGMLIB, DISP=SHR
//IMS DD DSN=IMSVS.PSBLIB, DISP=SHR
// DD DSN=IMSVS.DBDLIB, DISP=SHR
//SYSUDUMP DD SYSOUT=A
//HOSPSET DD DSN=IMS.VSAM.HOSPSET, DISP=OLD
//HOSPFLW DD DSN=IMS.VSA.HOSPFLW, DISP=OLD
//OUTPUT DD SYSOUT=A
//INPUT DD A
-------------------------------------
-------------------------------------
-------------------------------------
(INPUT TRANSACTIONS)
-------------------------------------
-------------------------------------

–Under IMS, the Batch Initialization Module DFSRRC00 is invoked via JCL which in turn loads
the application program and the DL/I modules required to service it.
–Under IMS, a batch DL/I program executes as a sub-program of DL/I even though the program
invokes DL/I services by issuing DL/I calls. The program and the DL/I modules execute together
–DFSRRC00 is the DL/I load module called as the Region Controller
–A convention, which is required for IMS-DC programs and optional for IMS-DB batch
programs, is that the Load module name and the PSB name should be the same. They are
specified in the PARM operand of EXEC statement. If the program name and PSB name is
different, DL/I allows to specify both names in the PARM operand.
–With the help of NAME operand in the PCB statement of PSB, IMS system loads into memory
the DBD of Database required
–With the help of DD names in the DATASET statement of DBD, the execution JCL describes
the physical file in the DD statements for the Database storage
–The other DD statements are required by DL/I
 6. DL / I PROGRAMMING
CONSIDERATIONS
- The application program is treated as a subroutine of DL/I and standard subroutine
Linkages and Parameter lists are used to connect the application program to the DL/I
modules that passes control to it.
- When DL/I links to the application program, it passes to the program a parameter list
containing the addresses of the PCB's in the PSB

OPERATING SYSTEM

DL / I
IMS
Address
PSB DBD
SPACE
Database
Or
REGION
APPLICATION PROGRAM

Figure 4 :- The Program Environment

6.1 WORKING STORAGE SECTION

- The DL/I Function Code variables are copied here

- The SSA'S (Segment Search Arguments) for segment retrievals are defined here
- The structure in COBOL for various segments within the database are declared
here, usually through a COPY statement
6.2 LINKAGE SECTION

- PCB masks for the PCB's passed to the program by DL/I is coded here
- The data names describe the data areas in the PCB mask for the PCB's that DL/I
loaded
- Must for every DL/I program since PCB is a DL/I control block that is loaded into
memory by DL/I before the program is executed.
- When a DL/I call is issued, the PCB mask must be specified to indicate which
PCB (database) in the PSB is to be used to process the call
- DL/I updates the PCB mask with the execution results after every DL/I call

The structure of a PCB mask is

LINKAGE SECTION
1 PCB-MASK
05 DBDNAME PIC X(8)
05 LEVEL-NUMBER PIC X(2)
05 STATUS-CODE PIC X(2)
05 PROC-OPTIONS PIC X(4)
05 JCB-ADDRESS PIC X(4)
05 SEGMENT-NAME PIC X(8)
05 KEY-LENGTH PIC S9(5) COMP
05 NUMBRE-SEGS PIC S9(5) COMP
5 KEY-FEEDBACK
07 HOSPNAME-KEY PIC X(20)
07 WARDNO-KEY PIC X(2)
07 BEDIDENT-KEY PC X(4)
PROCEDURE DIVISION
ENTRY 'DLITCBL' USING PCB-MASK

6.3 PROCEDURE DIVISION

- The entry code accomplishes three things in a program written in COBOL. They are
- It gives a standard DL/I name to the entry point of any COBOL - DL/I program
which must be DLITCBL
- It hooks the program to the PCB through the USING clause of the ENTRY
statement
- The sequence of PCB masks specified in the ENTRY statement must be identical
to the sequence of their corresponding PCB's in the PSB. Although the order of
PCB masks in the Linkage Section does not matter.
- The execution of a program terminates with a GOBACK statement because all
DL/I programs are sub routines of DL/I. Therefore, do not use STOP-RUN
- The ENTRY statement provides a mechanism for DL/I to transfer control to the
application program
6.4 DL/I CALLS
–Calls to DL/I are made using a DL/I interface language
–IMS services are requested via DL/I calls having a standard format
–The Language Components are
–The call statement parameter list
–The formats of the data items specified in that list
–DL/I calls can be imbed in COBOL, DL/I or Assembler
–The entry point name in the CALL statement is 'CBLTDLI' the name used whenever a
DL/I service is requested in a COBOL program
–The general command format is

CALL 'CBLTDLI' USING function code

PCB mask
I-O Area
SSA's

Function Code: - This is the first parameter in the list. It names a four byte
function code for the service requested from DL/I such as
Insert, Update, Delete, and Browse of database. A function
table Copybook called DLI CALLS is copied in the
application program using the command COPY DLI
CALLS

PCB Mask Name: - This is the second parameter in the list. It names the PCB
mask of the Database this DL/I call in use.
–After execution of the DL/I call, IMS will load the PCB
mask specified in the call with the execution result.
–The fields in the PCB mask structure are as follows

DBDNAME The DBD name of the database the call tried to manipulate
upto 8 characters long

LEVEL NUMBER The level number of the last segment encountered which
satisfied a level of the call. When the retrieval is
successfully completed, the level number of the retrieval
segment is placed in this field. The level number is two
bytes, Right Justified, Decimal Number field

STATUS CODE After the execution of every DL/I call, this field is updated
with a two-character code, which indicates the result of call
execution. If the execution is successful this field is blank
else appropriate status code for the service requested will
be returned by DL/I
PROCESSING This is a four byte left justified field in which the
processing

OPTIONS Options for the type of calls allowed in a program for the
database specified in the PCB statement of PSB is returned
by DL/I. The processing options are specified by
PROCOPT operand.

JCB ADDRESS This is a four byte field reserved for DL/I containing a four
byte address of an Internal Control Block called the JCB.
An area within JCB keeps track of the most recent calls.

SEGMENT NAME This is an eight-byte field with the name of the last segment
encountered which satisfied a level of the call. When the
call execution is successful, the name of the retrieved
segment is updated here, else the name of the segment
along the path that satisfied the search condition.

KEY LENGTH This is a field giving the length in bytes of the concatenated
key of all the segments along the key values of all the
segments along the retrieval path string together. This is a
four-byte field.

NUMBER OF This field contains the number of the segment types within
SEGMENTS the database to which the application program is sensitive
to as specified in the SENSEG statements of the PCB in the
PSB. This is a four-byte field.

KEY FEEDBACK Contains the actual concatenated key values of all the
AREA segments along the retrieval path upto the last segment
encountered which satisfied a level of the call. The key
fields are positioned from Left to Right, beginning with the
Root segment key value. This field is a variable field
structure depending upon the segments of a database. Rests
of the fields have a standard format and fixed length. This
field contains the key values or even though the segment
may be retrieved using a search field. A segment with NO
KEY field will skip that level in the concatenated key.
 INPUT-OUTPUT This is the third parameter in the list. This area is used by
AREA DL/I to put a retrieved segment or by the application
program to store the date of a segment prior to addition or
updation. If a single segment occurrence is received,
inserted or updated this area should be the segment layout
area. The I-O area must be large enough to contain the data
of the largest segment type. After determining which
segment is retrieved move the segment contents to an area
describing it. Another option is to use the REDEFINES
clause to describe each segment type in the Hierarchy path.

− Note
The first three parameters in the List Function Code, PCB address, I-O area are Required when
retrieving a segment using DL/I call. Optionally you can also specify a Segment Search
Argument to further describe and qualify the retrieval call.

6.5 Segment Search Argument: -

This is the fourth parameter in the list. This is optional. Whenever specified, DL/I uses it
to narrow the field of search to a particular segment type or to a particular segment
occurrence to be manipulated at each level of database. There can be maximum of 1 SSA
per level upto 15 SSA's for each database. If SSA is not used for any level, DL/I will
follow the rules to calculate the default SSA.

There are calls with three options: -

–Without SSA's
–With unqualified SSA's
–With Fully Qualified SSA's
–With combination of Qualified & Unqualified SSA's

For example, to retrieve a specific patient in a ward of a hospital will require 3 SSA's to
be coded in the card.

WORKING-STORAGE SECTION
1 PATIENT-SEGMENT
5 ------
5 ------
5 ------
1 HOSPITAL-SSA
05 FILLER PIC X(19) VALUE 'HOSPITAL (HOSPNAME = '
05 HOSPNAME PIC X(20)
05 FILLER PIC X VALUE ')'
1 WARD-SSA
05 FILLER PIC X (19) VALUE 'WARD (WARDNO ='
05 WARD NO PIC X(2)
 05 FILLER PIC X VALUE ')'
1 PATIENT-SSA
05 FILLER PIC X(19) VALUE 'PATIENT (PATNAME = '
05 PATNAME PIC X(20)
05 FILLER PIC X VALUE ')'
LINKAGE SECTION
1 PCS-MASK
-------
-------
-------
PROCEDURE DIVISION

CALL 'CBLTDLI' USING GU

PCB-MASK
PATIENT-SEGMENT
HOSPITAL-SSA
WARD-SSA
PATIENT-SSA
1 8 9 10 17 18 19 20 39 40
___________________________________________________________
HOSPITAL (HOSPNAME = RIVEREDGE )
WARD (WARDNO = 02)
PATIENT (PATNAME = BROWN )

The above three SSA's work together in a call to retrieve patient whose name is BROWN
from the ward no. 2 in hospital RIVEREDGE. This is a unique occurrence in HOSPITAL
database.

6.6 SSA STRUCTURE:

In an SSA one can provide
–The name of the segment type
–A description of the condition in a qualification expression
–One or more command codes that extends the function
 6.7 SSA TYPES:
There are two types

–Unqualified SSA :- This only specifies the SEGMENT TYPE the program is
interested in. Here you don't indicate a particular occurrence of a segment because you
don't care which occurrence of a segment you get. The segment name is first eight
characters padded by space upto the eighth position followed by a space in the ninth
position instead of a left parenthesis. For example - HOSPITAL. This will retrieve the
first occurrence of HOSPITAL segment.
–Qualified SSA: - This is addition to the SEGMENT TYPE, also contains one or more
qualification statements. A qualified SSA describes the segment occurrence a program
wants to access. This description is called a qualification statement having 3 parts. A
qualified statement is enclosed in parenthesis. The part names the field that DL/I will use
for segment search. The second part names the Relational Operator of two bytes telling
DL/I what kind of comparison to make during the search. The third part is a variable
length field that contains the values for comparison during DL/I search. Can code more
than one qualification statement.
–Fully Qualified SSA: - The SSA's give complete information about each segment
occurrence in the search hierarchy path.

− Note
In the ninth position of SSA
–A BLANK indicates unqualified SSA
–A LEFT PARENTHESIS indicates qualified SSA
An ASTERISK indicates one or more command codes
6.8 CALL TYPES
–Without SSA: - This is an unqualified call and DL/I assumes this to be an unqualified
SSA also for the ROOT segment Level. The first occurrence of root segment is retrieved.

–With Unqualified SSA: - This is a qualified call and DL/I will locate the first
occurrence of segment types specified in the call. For example
GU HOSPITAL
WARD
PATIENT

This will retrieve the first occurrence of PATIENT segment under the first occurrence of
WARD segment under the first occurrence of HOSPITAL segment.

–With Assumed Unqualified SSA: - If any segment type is either not specified for
any levels in the hierarchy path above the segment being retrieved (i.e. Missing Levels)
or is specified without any Qualification Statement (i.e. Skipped Levels), DL/I will
assume an Unqualified SSA for each missing or skipped segment types.

For example

(MISSING LEVEL ) GU PATIENT (PATNAME =KRISH )

(SKIPPED LEVEL ) GU HOSPITAL
WARD
PATIENT (PATNAME =KRISH )
The effect of both the calls is same.

–With Fully Qualified SSA: - To fully qualify a call so as to retrieve a particular

segment occurrence, you must specify a fully qualified SSA for that segment, and one for
each level above it. The SSA's must be coded in the hierarchical sequence of segment
types, starting with the root segment. You will however, retrieve only the segment
identified in the last SSA in the Parameter list and the others above it are used only to
further qualify the call, except in a special case involving SSA's using the D command
code.

For example:
GU HOSPITAL (HOSPNAME = MACNEAL )
WARD (WARDTYPE = INTENSIVE)

Any search field or the key field may be referenced in an SSA. The above example will
retrieve the segment WARD whose ward type is INTENSIVE. One SSA is needed to
retrieve the segment HOSPITAL, coded as
GU HOSPITAL (HOSPNAME = MACNEAL )
–With Combinations of Qualified and Unqualified SSA's: - The way DL/I
handles these calls depends upon the level at which the unqualified SSA's are coded.
 For example

GU HOSPITAL (HOSPNAME = RIVEREDGE )

WARD (WARDNO = 02 )
PATIENT

This will retrieve the first occurrence of the PATIENT segment in WARD No 02 of
Hospital name RIVEREDGE

For example

GU HOSPITAL
WARD
PATIENT (PATNAME = WHEELER)

Unqualified SSA's at higher levels such as HOSPITAL and WARD segment types and
qualified SSA's at the lower levels at PATIENT segment type only tells where DL/I is to
begin its search. DL/I does not limit its search to only those patient segment occurrences
under the first occurrence HOSPITAL. Instead, DL/I searches all the way through the
database until it reaches the occurrence of patient segment where the Patient is
WHEELER. In this case the two unqualified SSA's tell DL/I to locate the second segment
and start the search from there since we don't know in which Hospital and ward the
patient WHEELER is admitted.

− Note
Also specifying GU PATIENT (PATNAME = WHEELER ) wherein the segment types WARD &
HOSPITAL are skipped in the call. DL/I will assume an unqualified SSA for the skipped
segment types. The effect of the call is same as that of above example in which the levels are
expressly unqualified in the call.

6.9 DATABASE DL/I CALLS

There are five types of database DL/I calls. They are

GET CALLS (GU, GN and GNP)

GET HOLD CALLS (GHU, GHN and GHNP)
INSERT CALL (ISRT)
DELETE CALL (DLET)
REPLACE CALL (REPL)

6.10 RELATIONAL OPERATORS

Operator Meaning

= or EQ Equal
> = or GE Greater than or equal to
< = or LE Less than or equal to
> or GT Greater than
< or LT Less than
¬ = or NE Not equal to
 6.11 HOSPITAL DATABASE SEGMENT
OCCURRENCE CHART
1 HOSPITAL
MAC NEAL
2 WARD
01 / 018 / CARDIOVASC
3 PATIENT
VEENA / 0003 / 082377
4 PATIENT
SHEENA / 0008 / 071477
5 PATIENT
MEENA / 0017 / 091377
6 WARD
04 / 017 / GASTRO
7 PATIENT
HERO / 0004 / 051477
8 PATIENT
ZERO / 0008 / 060277
9 WARD
08 / 000 / INTENSIVE
10 PATIENT
WHEELER / 0001 / 081177
11 PATIENT
PEELER / 0002 / 080477
12 PATIENT
TRAILER / 0003 / 072877
13 PATIENT
BOILER / 0004 / 071877
14 PATIENT
JAILOR / 0005 / 080577
15 PATIENT
SAILOR / 0006 / 080177
16 HOSPITAL
RIVEREDGE
17 WARD
02 / 021 / PEDIATRIC
18 PATIENT
MUNNU / 0003 / 061477
15 PATIENT
CHUNNU / 0005 / 052277
20 WARD
04 / 008 / ORTHOPEDIC
21 PATIENT
6.12 RANDOM RETRIEVAL USING GU CALL
–This retrieves a unique segment occurrence randomly
–This is a fully qualified call wherein the program supplies a fully qualified SSA for each
level in the hierarchy down to the segment being retrieved.
–GU call is also used to set up the Parentage at the retrieved segment occurrence for the
subsequent GNP or GHNP calls issued in the program to retrieve its dependants
sequentially.

For example

GU HOSPITAL (HOSPNAME = RIVEREDGE )

WARD (WARDNO = 02 )
PATIENT (PATNAME = MUNNU )

This will uniquely retrieve the segment no. 18.

–Two status values are returned by DL/I in the status code field of PCB after executing
the call using GU function

BALNK - indicates the retrieval was successful

GE - indicates the segment occurrence was NOT FOUND

6.13 SEQUENTIAL RETRIEVAL USING GN CALL

–This retrieves a series of segments in Sequential order
–GN call is issued to retrieve the next segment occurrence from the current database
position established by a GU or GN call. DL/I will start the search from current position
forward to try to satisfy the call.
–Unqualified GN calls will traverse through the entire database
–One or more GN calls can be issued to retrieve the rest of the occurrences with the
duplicate key.
–After each call examine the PCB mask fields for the status code, segment name and
level number to determine the segment occurrence retrieved. Also it is difficult to figure
out when you will go up in level, go down in level, or stay at the same level in database.
–DL/I Sequential Processing sequence within a database is always Top to Bottom, Left to
Right and Front to Back along Twin occurrences.
 1
Root Level HOSPITAL 15

2 16
Second Level WARD 13 WARD

3 14 17
Third Level PATIENT 9 PATIENT PATIENT

10 11 12 18 19
Fourth Level SYMPTOM TREATMNT DOCTOR SYMPTOM TREATMNT

20

21

4 5 7 22
SYMPTOM TREATMNT 6 DOCTOR 8 DOCTOR

Figure 5

− Note
1. Reading sequentially through the database with an unqualified GN call, will retrieve different
segment types at different levels
First call retrieves a segment at the first or Root level (1)
Second call retrieves a segment at the second level (2)
Third call retrieves a segment at the third level (3)
Fourth call retrieves a segment at the fourth level (4)
Fifth, Sixth, Seventh, Eighth call retrieves segments at fourth level (5,6,7,8)
Ninth call retrieves a segment at the third level (9)
Tenth call retrieves a segment at the fourth level (10)
Eleventh & Twelfth call retrieves segments at the fourth level (11, 12)
Thirteenth call retrieves a segment at the second level (13), thereby moving from
Level four to level two in one call.
2. An important issue to be considered in sequential calls is the concept of position within the
database.

6.14 GN calls without SSA's (unqualified GN calls)

–DL/I looks at the current position within the database and retrieves the next segment in
hierarchical sequence
–Issuing a GN call without SSA as the first call in the program is equivalent to issuing a
GN call without SSA. Since both retrieves the first segment in database, the first
occurrence of root segment.
–Segments are retrieved all the way to the end of the database

Call 'CBLTDLI' using GN

PCB-Mask
I-O Area

6.15 GN call with Unqualified SSA's (Qualified GN call)

–GN calls with unqualified SSAs lets the sequential retrieval restricted to only a
particular segment type, no matter what segments they are dependent upon.

For example: - GN PATIENT

When issued at the beginning of program execution, position would be established at the
beginning of the database; and the call would retrieve the first patient segment 3. Next
issue of the same call will retrieve the next patient occurrence in segment 9. Next issue of
the same call will retrieve the next patient occurrence in segment 14. Next issue of the
same call will retrieve the next patient occurrence in segment 17. Finally, the next issue
of the same call would cause DL/I to return a GB status code since no more patients
segments exist in the Hospital Database.

6.16 GN call with Qualified SSA's (Qualified GN Call)

–One strong reason to issue a qualified GN call instead of a GU call is to implement
Skip-Sequential Processing
–In this, segments are always processed in their KEY SEQUENCE
–In Skip-Sequential Processing selected segments are processed in hierarchical sequence,
with the restriction that the search values are presented to the program in Ascending
sequence. If any search value that is lower than the value used in the previous call is
provided, DL/I will return a GE status code, which is segment not exists. However, a GU
call will go back to the beginning of database to find and retrieve the segment to the
program whatever be the search values.
 6.17 GN Calls - STATUS CODES
–When issued without SSA's (unqualified GN call) three values are returned
–GA - Moved up in level to retrieve the segment
–GK - New segment type at the same level is retrieved
–GB - End of database is reached
–When issued with Unqualified SSA's (Qualified GN call) one value is returned
–GB - End of database is reached
–When issued with qualified SSA's (Qualified GN call) two values are returned
–BLANK - Segment successfully retrieved
–GE - Segments not found following the current position

− Note
–The above status codes do not indicate error conditions
–Each GN call that retrieves a segment of the same type, or retrieves a segment lower in the
hierarchy than the last one will return a BLANK status code.
–GA does not tell how many levels up, the position moved since the last call.
–One more GN call after returning a GB status code, DL/I will position itself at the beginning of
the database.
6.18 SEQUENTIAL RETRIEVAL USING GNP CALL
–Performs sequential retrieval very similar to the GN function, except that it retrieves
only segments that are subordinate to the currently established parent.
–Parentage must be established by issuing either a GU or GN call, in which case DL/I not
only establishes a position on same segment occurrence, but it also, establishes parentage
on that occurrence.
–The segment retrieved by the GN or GU call is treated as the parent segment for any
subsequent GNP calls issued in the program.
–The GNP calls return only those segment occurrences that are

6.19 GNP calls without SSA's (Unqualified GNP call)

–Issuing a series of GNP calls without SSA's will retrieve only those segments that are
dependant on the segment at which the parentage is established

GU HOSPITAL (HOSPNAME = Mac Neal)

Assume this establishes parentage; say at segment 1 in database.

–Next GNP call without SSA will retrieve the first word segment that is segment 2
–Further GNP calls without SSA will scan through the database and retrieve in
hierarchical sequence all the segments that are dependent on Mac Neal Hospital Segment.
The last one being segment 14
–One more GNP call after segment 14 would return a status code of GE indicating no
more segments under the established parent. That is segment no.1
–The lower in level that parentage is established, the fewer segments an unqualified GNP
call has access to.

GU HOSPITAL (HOSPNAME = Mac Neal )

WARD (WARDNO = 01 )
PATIENT (PATNAME = MUNNU )

Assume this establishes parentage; say at segment 3 in database, the patient segment for
patient Munnu.
–Next GNP calls without SSAs would only have access to segments 4, 5, 6, 7, and 8 in
the database
–One more GNP call after segment 8 would return a status code of GE indicating no
more segments dependant on segment 3. That is the patient name MUNNU.
6.20 GNP call with Unqualified SSA's (Qualified GNP call)
–GNP calls with unqualified SSA's will sequentially retrieve only segment of the
particular segment type.

GU HOSPITAL (HOSPNAME = Mac Neal)

Assume, this established parentage, say at segment 1 in database.

GNP PATIENT

In this case, GNP calls that specify an unqualified SSA for the Patient segment retrieves
the segments 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 and 14 in the first database record that is
segment no. 1 for Mac Neal Hospital

However, if an unqualified GNP calls are issued with segment no. 1 as the established
parent, even ward segments no. 2 and 13 would be retrieved as well in the sequence along
with the above segments.

− Note
–Results could be dramatically wrong if a mistake is made in establishing parentage before
issuing GNP calls.
–While coding a qualified GNP call do not include SSA's for segments at a level higher than or
equal to that of the currently established parent segment. If you do, DL/I will return a GP status
code.
6.21 GNP call with Qualified SSA's (Qualified GNP call)
–GNP calls with qualified SSA's can be used when performing Skip-Sequential
Processing.
–Perform a series of GNP calls using SSA only for the segment type being retrieved.

GU HOSPITAL (HOSPNAME = Mac Neal )

WARD (WARDNO = 01 )

Assume, this established parentage at ward no 01 in Mac Neal Hospital, say at segment 2
in the database.

GNP PATIENT (BEDIDENT = Supplied Value)

Now, issuing GNP calls with a single qualified SSA for the patient segment instead of
GN calls, the program has automatically limited the area of search to only there segments
which are dependant on ward no. 1. That is segment 2.

If GNP calls are replaced y GN calls with the single SSA, this would read through all the
patient segments in the database, rather than stopping at the end of Ward No. 1 segment.

6.22 GNP Calls - STATUS CODE

–When issued without SSA's (unqualified GNP call)
–GA - Moved up in level to retrieve the segment
–GK - New segment type at the same level is retrieved
–GE - End of database is reached
–When issued with unqualified SSA's (qualified GNP call)
–GE - End of database is reached
–When issued with qualified SSA's (Qualified GNP call)
–BLANK - Segment successfully retrieved
–GE - Segments not found following the current position

− Note
–A GP error code is returned by DL/I, which almost always represent a Programming ERROR as
below :-
–If a GNP call is issued without first establishing parentage on a segment by a GU or GN call.
–If the GU or GN call is issued to establish the parentage is not executed successfully before the
GNP call was issued.
–An established parent segment is deleted before the GNP call depending on that parent is
issued.
–If the SSA's coded in the GNP call contains errors
 7. UPDATING AND DELETING
SEGMENTS
–Updating and Deleting segments always requires the program to perform a sequence of
two calls.
–The first call being a GET HOLD function to retrieve the segment that the program
intends to Update or Delete
–The second call being a REPL or DLET function to perform the replacement or deletion
of the segment eventually.
–Any intervening calls between the first and the second call will nullify the effect of the
GET HOLD call. The practical implication of this is that the program can proceed with
the other processing if it is decided not to go ahead with the replacement or the deletion
of the segment. Hence any explicit action to cancel the effect of a get hold call is not
required in the program.

7.1 GET HOLD CALLS

–Are GHU, GHN, GHNP
–Perform similar functions of GU, GN and GNP apart from certain additional functions
such as
–DL/I saves information about the segments location
–DL/I writes information in system log data sets, which are used to restore a
database should recovery is ever necessary.
–Same kind of SSA's used with normal calls can be used with Get Hold calls to
bring a particular segment into the I-O area
–Status codes returned by DL/I are also identical, given the similar circumstances

7.2 DELETE AND REPLACE RULES

Rule No.1 - Must issue a Get-Hold call prior to issuing a REPL or DLET function call

Rule No.2 - Should not issue any other call using the same PCB, between the time a
Get Hold call is issued and the time a Replace or Delete call is issued, unless that other
call is also a Get Hold call.

Rule No.3 - Should not normally code SSA's in the Replace or Delete calls except
when the Get Hold call is with one or more SSA's using the D command code.

Rule No.4 - The KEY field in the segment cannot be modified before the REPL or
DLET calls.
7.3 REPLACING SEGMENTS IN THE DATABASE
USING THE REPL FORM
–Must issue a Get Hold call to retrieve the segment data into I-O area.
–Changes can be made to the data in I-O area except the KEY field.
–Issuing a REPL call will cause changes to the segment to be rewritten to the database.
–If the Get Hold call is a Path call issued with one or more SSA's using the D command
code, a REPL call can be issued with SSA's
–The SSA's can be Qualified or Unqualified
–The SSA's must use N command code for those segments whose data you DON'T want
to be rewritten to the data.
–If the REPL call is issued without SSA's, it operates all the segments retrieved along the
path and all the segments in the path will be rewritten to the database.

CALL 'CBLTDLI' USING GHU

PCS-MASK
PATIENT I-O AREA
HOSPITAL-SSA
WARD-SSA
PATIENT-SSA

Make appropriate changes to Patient segment data.

CALL 'CBLTDLI' USING REPL

PCB-MASK
PATIENT I-O AREA

7.4 REPL CALL - STATUS CODE

DJ - Replace call issued without an immediately preceding GETHOLD call.
DA - Program has changed the segment's key field
RX - Encountered a Replace Rule Violation
AJ - Used an SSA without command code in the REPL call
7.5 DELETING SEGMENTS IN THE DATABASE
USING THE DLET FUNCTION
–Must issue a Get Hold call to retrieve the segment data into the I-O area
–Issuing a DLET call will cause the segment to be deleted, and automatically deletes all
its subordinate occurrences from the database
–If the Get Hold call is a path call issued with one or more SSA's using the D command
code, a DLET call be issued with SSA
–SSA can only be unqualified (i.e. no command codes)
–A DLET call using an Unqualified SSA without a command code will cause the segment
named by the SSA to be deleted along with all its dependants. However, segments above
it will not be deleted.
–A DLET call without SSA following a Get Hold path call operates on the entire path
deleting all the segments in the path being retrieved.
–A DLET call without SSA following a normal Get Hold call will only delete the
segment specified in the last SSA of Get Hold

CALL 'CBLTDLI' USING GHU

PCB-MASK
PATIENT I-O AREA
HOSPITAL-SSA
WARD-SSA
PATIENT-SSA

7.6 DLET CALL - STATUS CODES

DJ - Delete call issued without an immediately preceding Get Hold call
DA - Program has changed the segment's KEY FIELD
DX - Encountered a Delete Rule Violation
AJ - Used an SSA which is Qualified
8. INSERTING SEGMENTS INTO AN
EXISTING DATABASE
–ISRT call is issued to insert a new segment into the database. Insertion of segments can
be made in any sequence.
–Program should build the segment occurrence data in the segment description area in
Working-Storage section before issuing a call.
–PCB for the database in the PSB should specifying as processing options I or IS in the
PROCOPT operand for permitting insertions of segments in the Ascending Sequence in
the Insert Mode. (A or AS is also permitted)
–If the ISRT call is issued with an unqualified SSA, DL/I will try to insert the segment
based on the current position in the database. The current position is established by a
previous retrieval call, followed by an Insert call using the unqualified SSA for the
segment to be inserted.

GU HOSPITAL (HOSPNAME = Mac Neal)

WARD (WARDNO = 01 )
ISRT PATIENT

–If the ISRT call is issued with a qualified SSA, describing the path along with the
insertion is to be made, with an unqualified SSA for the segment being inserted with an

ISRT HOSPITAL (HOSPNAME = Mac Neal )

WARD (WARDNO = 01 )
PATIENT

–If the inserted segment occurrence has a unique key field DL/I uses the key of the new
segment to determine where
 9. DBD INSERT RULES
–When DBA defines a segment type that does not have a key field, or has a non-unique
key field, it is necessary to tell DL/I where to insert the new segment occurrences for that
segment type in the twin chain.
–The RULES operand of the SEGM statement of DBD tells DL/I how to handle segment
insertions in such situations.
–RULES operand has three options that tells DL/I where in the twin chain to insert the
new segment which does not have a unique key field. They are as follows

FIRST - Says that the new segment will always be inserted at the beginning of the twin
chain.
LAST - Says that the new segments will always be inserted at the end of the twin chain.
This is the default.
HERE - Says that the new segment will be inserted after the segment at which the
program within the twin chain establishes the current position before the ISRT call is
issued. If the current position is not established before inserting the new segment, with
this rule, a new segment occurrence is always inserted at the beginning of the twin chain
if no position is established within the twin chain.

–DL/I uses the key field to find the approximate position within the twin chain to insert
an segment that has non-unique key field. The insert rule is then applied to determine
where to insert the new segment occurrence relative to all the segments having the same
non-unique key value. First, tells DL/I to insert the new segment at the beginning of all
those segments having the same non-unique key value. Last, tells DL/I to insert the new
segment after all those segments having the same non-unique key value. Here, tells DL/I
to insert the new segment within the twin chain after establishing the current position
within it. If the appropriate key value position is not established, DL/I will insert the new
segment at the beginning of the set of segments having the same key value.

9.1 ISRT CALL (INSERT MODE) - STATUS CODE

II - The segment already exists in the database. A duplicate key value is being inserted
into.

IX - Encountered an Insert Rule Violation. Program tried to insert a segment into the
wrong place in the database. For example: A patient segment is being inserted under the
Facility segment, when it is in fact dependent upon the Ward segment.
9.2 LOADING SEGMENTS INTO AN EMPTY OR
SCRATCH DATABASE
–ISRT call is also issued to load a database with segments from the scratch
–PCB for the database in the PSB should specify as processing options L or LS in the
PROCOPT operand for permitting loading of segments in the Ascending sequence in the
Load mode
–Insert commands in Load Programs normally load segments in Ascending sequence
only with certain exceptions.
–One important rule for ISRT call is that the segment being loaded or inserted must be
identified in an single unqualified SSA, since qualified SSA is not valid.
–Programs designed to Load databases normally use ISRT calls with Unqualified SSA
–Segments must be presented to the Load Program in the Hierarchical Sequence. It
means that root segments must be presented to the load program in root key sequence and
all dependant segments must be presented in hierarchical sequence following each root
key.
–The appropriate segment name for the segment type being loaded is moved into the
Unqualified SSA are before
–DL/I gets the Qualification information for the segment being inserted from I-O area
–It is however valid to include Qualified SSA's to completely describe the path with a
restriction that the SSA for the segment being loaded cannot be qualified. Also, you
cannot include SSA's at levels lower than the level at which the segment is being loaded.

CALL 'CBLTDLI' USING ISRT

PCB-MASK
I-O AREA
UNQUALIFIED-SSA

9.3 ISRT CALL (LOAD MODE) - STATUS CODES

LB - When you try to load the same segment twice i.e. segment already exists
LC - The segments being loaded are not in their Hierarchical sequence i.e. key values out
of sequence
LD - No parent for the segments being loaded. You cannot load a dependant segment
until its parent has been loaded.
LE - Segment types out of sequence. For example: - If you tried to load a facility segment
before a patient segment.
 10. ADVANCED DATABASE
PROCESSING
10.1 BOOLEAN SSA STATEMENTS
–Sometimes an SSA needs more than one qualification statement when there are more
than one condition to be tested to qualify at that segment.
–The conditions are tested on more than one field in a segment Boolean Operators are
needed to connect these qualification statements.
–The valid Boolean Operators are
* (Asterisk) or the & (Ampersand) -------> Logical AND
+ (Plus) or the | (Vertical Bar) ---------> Logical OR
–DL/I can evaluate any complex group of qualification statements. A group of
qualification statements connected by AND operators is called a SET of qualification
statements.
–In order for the entire expression to be satisfied, any one set of qualification statements
needs to be satisfied.
–In order for the set to be satisfied, all the qualification statements within that set must be
satisfied.
–If AND and OR operators are used in a single SSA, group all the statements connected
by the AND operators as a SET.
–First AND is evaluated, then OR as per normal Logic Rules.
–For example

GU Segment ( A = 1 * B =2+C =3 * D =4)

A = 1 AND B = 2 OR C = 3 AND D = 4

Qualification Qualification Qualification Qualification

Statement AND Statement Statement AND Statement

Set of qualification statements Set of qualification statements

OR

TEST EXPRESSION
10.2 SSA'S USING COMMAND CODES
–Command codes in a SSA makes the call powerful since DL/I treats such SSA'S
differently from those without the command codes while performing some special
functions.
–Command codes save programming and processing time
–Command codes are specified in an SSA following the segment name and an Asterisk '*'
–An Asterisk '*' in the ninth position in a SSA indicates that one or more command codes
follow the asterisk
–A Blank or Left Parenthesis marks the end of command codes
–ONE or MORE command codes can be used in any combination
–Ten command codes are available under IMS
F - Locate First Occurrence
L - Locate Last Occurrence
D - Retrieve this segment data into the I-O Area (Path Call)
N - Do not replace this segment
C - Concatenated key in this SSA
Q - Enqueue this segment
U - Maintain current position at this level
V - Maintain current position at this and higher level
P - Establish Parentage at this level
- - Null command code
–Command codes in a Qualified SSA
WARD*D(WARDNO=03)
WARD*DNP(WARDNO =03)
–Command codes in an Unqualified SSA
WARD*PD
10.3 F COMMAND CODE
–Tells DL/I to begin the search with the first occurrence of this segment type in a twin
chain under its parent.
–It can be used only with GN, GNP, GHN and GHNP calls
–In a retrieved call this command code allows the segment occurrence to be inserted as
first occurrence in the segment type which has non-unique or no key field and
RULES=HERE is specified for this segment in the DBD.
–Suppose you search through all the treatment segments under a particular patient
segment occurrence for a treatment type of Morphine. If you find one, you would like to
print all the Treatment occurrences for that patient.

WITHOUT COMMAND CODE

1. GU HOSPITAL (HOSPNAME = RIVEREDGE )

WARD(WARDNO = 04 )
PATIENT (BEDIDENT = 08 )
2. GNP TREATMNT (TRTYPE = MORPHINE )
3. If status code is GE, exit from procedure, Else if Blank
4. GU HOSPITAL (HOSPNAME = RIVEREDGE )
WARD(WARDNO = 04 )
PATIENT (BEDIDENT = 08 )
5. GNP TREATMNT
6. Print a treatment segment occurrence
7. Loop back to step 5 until a GE status code

WITH COMMAND CODE

1. GU HOSPITAL (HOSPNAME = RIVEREDGE )

WARD(WARDNO = 04 )
PATIENT (BEDIDENT = 08 )
2. GNP TREATMNT (TRTYPE = MORPHINE )
3. If status code is GE, exit from procedure, Else if Blank
4. GNP TREATMNT * F
5. Print a treatment segment occurrence
6. GNP TREATMNT
7. Loop back to step 5 until status-code GE
10.4 L COMAMND CODE
–Tells DL/I to retrieve the last occurrence of this segment type in a twin chain under its
parent
–In an insert call this command code insert the segment occurrence as the last occurrence
in the segment type which has non-unique or no key field.
–L command code can be used only in the dependent segment types. It is ignored, if used
in the root segment.
–Suppose you want to retrieve the last twin occurrence of the Treatment Segment type for
a particular patient segment.

WITHOUT COMMAND CODE

1. GU HOSPITAL (HOSPNAME = Mac Neal )

WARD(WARDNO = 08 )
PATIENT (BEDIDENT = 04 )
2. GNP TREATMENT
3. Loop back to step 2 until status code is GE. When GE, the I-O area will contain the last
twin occurrence of treatment.

WITH COMMAND CODE

1. GU HOSPITAL (HOSPNAME = Mac Neal )

WARD(WARDNO = 08 )
PATIENT (BEDIDENT = 04 )
TREATMNT * L
10.5 D COMMAND CODE & N COMMAND CODE
–D & N command codes work together to process multiple segments in a single call.
–D command code performs a PATH call, wherein, DL/I retrieves multiple segments
along the retrieval path in the I-O area. Thus the I-O area must be defined large enough to
accommodate all the segments being retrieved in the path. DL/I will place the segment at
the higher level in front of the segment at the lower levels. The segment layouts within
the I-O area must be defined in the hierarchical structure.
–If D command code is not coded, only the segment identified by the last SSA is placed
in the I-O area by default. Necessary to retrieve all the segments in the hierarchical path.
Therefore, you can code D command code in the higher level SSA's only for those
segments you want DL/I to place in the I-O area.
–A processing option of P must be coded in the PROCOPT operand of the PCB in your
PSB for the segment, if D command code is to be used in an SSA for that segment.
PROCOPT = P
–DL/I remembers how many segments are stored in the I-O area by the Get Hold path
call. So a subsequent replace call without SSA's will replace all the segments in the I-O
area along the path.
–N command code is coded in the SSA'S for those segments used in the Replace call that
you don't want to Replace.
–SSA'S with the N command code is an exception to the rule that qualified SSA'S cannot
be coded in a Replace call.
–One can code a combination of D and N command codes within the same SSA if the
same sets of SSA'S are used in both the Get Hold Path Call and the Replace Call.

WITH D COMMAND CODE

GHU HOSPITAL *D (HOSPNAME = RIVEREDGE )

WARD* D (WARDNO = 02 )
PATIENT (BEDIDENT = 0005 )

WITH N COMMAND CODE

REPL HOSPITAL *N (HOSPNAME = RIVEREDGE )

WARD* N (WARDNO = 02 )
PATIENT (BEDIDENT = 0005 )

WITH D & N COMBINATION

Both for GHU & REPL

HOSPITAL * DN (HOSPNAME = RIVEREDGE )
WARD* DN (WARDNO = 02 )
PATIENT (BEDIDENT = 0005 )
–D command code in one or more higher level SSA'S will also place the additional
segment in lt I-O area. It is not if SSA omitted default n replace all implicit N will be
ignored for Get and D W.

10.6 RETRIEVING AND REPLACING WITHOUT

COMMAND CODE
1. GU HOSPITAL (HOSPNAME = RIVEREDGE )
2. Save Hospital information
3. GN WARD(WARDNO = 02 )
4. Save Ward information
5. GHN PATIENT (BEDIDENT = 0005 )
6. Print Patient, Ward and Hospital information
7. Update information in the Patient segment
8. REPL

10.7 C COMMAND CODE

–C command code is used in situations where you would normally use fully qualified
calls.
–It allows you to use a concatenated key value in a single SSA rather than using a set of
fully qualified SSA'S
–The concatenated key must be enclosed in Parenthesis and no key in the path can be
omitted from the concatenated key.
–Only a single SSA naming the segment to be retrieved can be used in the call with C
command code.

WITHOUT C COMMAND CODE

GU HOSPITAL (HOSPNAME = RIVEREDGE )

WARD(WARDNO = 02 )
PATIENT (BEDIDENT = 0003 )
DOCTOR (DOCTNAME = KILLER )

WITH C COMMAND CODE

GU DOCTOR * C (RIVEREDGE 02 0003 KILLER )

CALL 'CBLTDLI' GU
CONCATENATED-KEY
1 CONCATENATED-KEY
05 SEG-NAME PIC X (08)
5 CON-CODE VALUE 'X C '('
5 HOSP-KEY X (02)
05 WARDKEY PIC
5 CLOSE X (01) VALUE ')'
10.8 Q COMMAND CODE
–Q command code is only used when multiple applications will be accessing the same
database at the same time. Normally used in the O/L MPP where the O/L programs are
running under multitasking environment and more than one task can update the same
database at the same time.
–If you do not want this to happen, issue DL/I calls with Q command code to ENQUEUE
the particular segment occurrence for exclusive use by your task, preventing other online
transactions from updating the segment until your task is completed.
–Other users cannot make a Get Hold type call for that segment, only get calls can access
that segment. Get Hold type calls must wait until the Enqueued segment has been
Dequeued through the DEQ call, CHKP call, or the program termination.
–Q command code set at the root segment level will not allow any other user to gain
access to any segment in that database record.
–A one-byte class identifier in the range of 'A 'through' J follows Q command code. This
class identifier must be specified in the DEQ call to dequeue the segments.

GHU HOSPITAL WQB ( HOSP = APPDO )

WARD(WARDNO = 05)
PATIENT (= MUNNU)

10.9 U AND V COMMAND CODES

–U and V command codes are used to prevent a GN or GNP call from leaving the current
position.
–They help exercise some control over calls that cannot be satisfied for a particular
parent, but can be satisfied further in the database under a different parent.

WITHOUT U COMMAND CODE

1. GU (HOSPITAL ( HOSPNAME = Mac Neal )

2. GNP WARD
3. GET A WARD KEY FROM PCB AND STORE IN WARD SSA
4. GNP WARD (WARDNO = WORDKEY)
PATIENT
5. LOOP BACK TO STEP 4 UNTIL A GE STATUS CODE

In the above example you have to get the key value of the ward segment out of the PCB
every time Step 2 of the procedure is executed. Store the key value into the qualified SSA
in Step 4 before starting the loop that retrieves the Patient segments. This keeps the GNP
calls within the same domain in the database. GE status code is returned by DL/I after
you run out of Patient segments for each Ward, just as though you had established
parentage at the Ward Level for getting the necessary Control Breaks.
 WITH U COMMAND CODE

1. GU HOSPITAL (HOSPNAME = Mac Neal )

2. GNP WARD
3. GNP WARD * U
PATIENT
4. LOOP BACK TO STEP 3 UNTIL A GE STATUS CODE

In the above example coding a U command code in an unqualified SSA has the same
effect as using a qualified SSA at that level. Using U command code at the ward level
tells DL/I to maintain the current position established on the ward segment level.

WITH V COMMAND CODE

GNP WARD * U
PATIENT * U
SYMPTOM
(OR)
GNP PATIENT * V
SYMPTOM

In the above example, V command code causes DL/I to act as though U command code
were set at that level, and at all the levels above it. The two sets of SSA'S are functionally
the same. The command saves the trouble of coding U command codes in SSA'S at each
higher level.

10.10 P COMMAND CODE

–P command code allows the parentage to be set at any levels in the database other than
the one identified by the last SSA
–Code the P command code in the SSA for the segment at which you would like the
parentage established and DL/I will still retrieve the segment identified by the last SSA,
but sets parentage where you set the P command code.
–The parentage will be destroyed when another GU or GN call is executed.

WITH P COMMAND CODE

1. GU HOSPITAL (HOSPNAME = Mac Neal )

WARD(WARDNO = 08 )
2. GNP PATIENT
3. PRINT A PATIENT SEGMENT
4. LOOP BACK TO STEP 2 UNTIL A GE STATUS CODE
 WITH P COMMAND CODE

1. GU HOSPITAL (HOSPNAME = Mac Neal )

WARD* P (WARDNO = 08 )
PATIENT
2. PRINT A PATIENT SEGMENT
3. GNP PATIENT
4. LOOP BACK TO STEP 2 UNTIL A GE STATUS CODE

By using a P command code, you saved one call by retrieving the first patient segment in
the Get Unique call itself and setting the parentage at the ward level.

10.11 NULL COMMAND CODE

–The NULL command code '___ ' is used in the SSA to simplify the construction of SSA
within the program and does not perform any function at all.
–The SSA is treated as if no command code were coded.
–The null command code '__' reserves one or more positions in a SSA into which you can
store command codes during the program execution. This way making it possible to use
the same set of SSA'S for more than one purpose.
–HOSPITAL *------- (HOSPAME = Mac Neal )
10.12 MULTIPLE POSITIONING WITHIN THE PCB
–With Multiple Positioning DL/I maintains a unique position within a Database Record
for each dependent segment type at each level in each Hierarchical path in the database.
–Multiple Positioning is normally used to access segments of two or more types
dependent on a specific parent.
–The segments are processed sequentially at the same time, enabling parallel processing
within the database.
–Multiple Positioning lets a program maintain more than one position within a database
using a single PCB.
–Multiple Positioning for a database is specified in the PCB statement in the PSB for
POS operand. For example
PCB TYPE=DB, NAME=HOSPITAL, POS=M or S
M stands for Multiple, S stands for Single Positioning
If POS operand is not coded, the default is single positioning
–It is important for a programmer to know what is in effect for your PCB before coding
the program. Since it is dangerous to change the parameter from M to S in the POS
operand for the PCB
 HOSPITAL 1

WARD 2 FACILITY 20

PATIENT 3

PATIENT 13

SYMPTOM 14 TREATMNT 16 DOCTOR 18

15 17 19

SYMPTOM 4 TREATMNT 7 DOCTOR 10

5 8 11

6 9 12

Figure 6

–In the above Hierarchy assume that there is a one to one relationship between
SYMPTOM, TREATMNT and DOCTOR segments. For each SYMPTOM segment there
must be a corresponding TREATMNT and DOCTOR segments. This type of relationship
between the segment types in the database illustrates the need for Multiple Positioning
for some types of Sequential Retrievals

–Suppose we want to print for a PATIENT segment each set of SYMPTOM,

TREATMENT and DOCTOR segments under that PATIENT and we don’t care about the
sequence of the segments.

GU HOSPITAL (HOSPNAME = RIVEREDGE)

WARD(WARDNO = 02 )
PATIENT (BEDIDENT = 1012 )

With the above sequence of calls we will first retrieve all the SYMPTOM segments,
followed by all the TREATMNT segments, followed by all the DOCTOR segments.
However, this is not what we want because what we really like to do in this case is to first
retrieve the SYMPTOM segment, followed by a TREATMNT segment, followed by a
DOCTOR segment.

Suppose we code as follows

GU HOSPITAL (HOSPNAME = RIVEREDGE)

WARD(WARDNO = 02 )
PATIENT (BEDIDENT = 1012 )
GNP SYMPTOM
GNP TREATMNT
GNP DOCTOR

This will work only for the first execution of above call sequence retrieving segments 4, 7
and 10. But the second execution will return a GE status code indicating there are no
more SYMPTOM segments under that Parent i.e. PATIENT whose BEDIDENT = 1012.
To get the next SYMPTOM segment, DL/I will have to remember the position of the last
SYMPTOM segment retrieved, as well as the positions of the last TREATMNT and
DOCTOR segments.

Suppose we code
 GU HOSPITAL (HOSPNAME = RIVEREDGE)
WARD(WARDNO = 02 )
PATIENT (BEDIDENT = 1012 )
GN SYMPTOM
GN TREATMNT
GN DOCTOR

This time the sequence of segments retrieved will be 4, 7, 10, 14, 16, 18 followed by a
GE status code. This call sequence will go through the entire database retrieving only the
first occurrence of the SYMPTOM, TREATMNT and DOCTOR segment under each
PATIENT segment.

Now, retrieving with Multiple Positioning, DL/I maintains a separate Unique position
within the Database Record for each Dependent Segment Types at each level in each
Hierarchical Path. A chart below illustrates this

HOSPITAL

A WARD B FACILITY

C PATIENT

D SYMPTOM E TREATMNT F DOCTOR

Figure 7

− Note
That you cannot maintain two positions on the same segment type. Also, the separate positions
are maintained only on the segments dependent upon a particular parent.

Suppose we code as follows

 GU HOSPITAL (HOSPNAME = RIVEREDGE)
WARD(WARDNO = 02 )
PATIENT (BEDIDENT = 1012 )
GNP SYMPTOM
GNP TREATMNT
GNP DOCTOR

Assuming that Multiple Positioning is in effect, the first time we retrieve segments 4, 7
and 10. The second time we retrieve segments 5, 8 and 11 using GNP calls. The third
time we retrieve segments 6, 9 and 12 using GNP calls.

This is possible because DL/I maintains a different position for each segments at D, E
and F in the hierarchy chart above.

10.13 MULTIPLE PCB's IN A PSB

–When a program needs access to more than one database, it has a PCB for each.
–A single PCB can refer to only one DBD
–Multiple PCB's can also be defined for a single database in which case the program has
two or more views of the same database and DL/I will maintain a unique position in that
database for each PCB you define on it.
–Multiple PCB's on the same database is defined when the program require access to two
completely different logical data structures, each describing different segments in
different hierarchical paths from the same database.
–Each PCB in SPB has its own PCB mask in the Linkage Section and is specified in the
ENTRY statement for addressing that block in the order in which PCB's appear in the
PSB.
–Multiple Positioning enables processing within one portion of a Database record
parallely wherein, the program processes different segment types in parallel as long as
those segment types are dependant upon the SAME parent whereas, Multiple PCB's
allow the program to process the segments in parallel, no matter where in the database the
segments are
–A good example of where parallel processing using Multiple PCB will be in
Transferring a Patient from one hospital ward to another hospital ward. To do that you
first retrieve a patient segment from one part of database and insert it in another part of
the database. You will then sequentially process that transferred patient's SYMPTOM the
new place of the PATIENT segment.
–With a single PCB, as soon as you insert the PATIENT segment under a new WARD
segment occurrence, you lose position on the old PATIENT segment and finding its
dependents will be difficult without retrieving the old PATIENT segment again. Also
each time your insert one of the dependants under the new parent you lose position again.
–Suppose you define two PCB's and both of them describe the same Logical Data
Structure. You need two PCB's so that you can maintain two positions in different parts of
the database simultaneously.
Suppose we code as follows
 Call 'CBLTDLI' using GU
PCB1-MASK
I-O AREA
OLD HOSPSSA
OLD WARDSSA
OLD PATIENTSSA

Call 'CBLTDLI' using ISRT

PCB2-MASK
I-O AREA
NEW HOSPSSA
NEW WARDSSA
PATIENTSSA-UNQUALIFIED

Call 'CBLTDLI' using GNP

PCB1-MASK
I-O AREA

Move PCB1-Segment Type to New-Unqualified-SSA

Call 'CBLTDLI' using ISRT

PCB2-MASK
I-O AREA
New-Unqualified-SSA

10.14 LOGICAL DATABASES

–A logical database is normally used to combine segments from more than one Physical
Database into a NEW hierarchy structure using the logical relationships
 –A Physical Database is used to describe the physical structure of a database and the
hierarchical relationships between the segment types.
–Logical Relationships allow the DBA to define new hierarchical relationships without
actually having to create a new physical database.
–DBDGEN process can also be used to define Logical Database.

10.15 LOGICAL RELATIONSHIPS

–It is a path between segments that otherwise would be unrelated. This relationship is
always between two segments
–The two segments may reside in separate physical databases, though they can also be
within the same database physical.
–The basis of a logical relationship is a segment called the Logical Child segment. The
Logical Child is a physical database segment having two parents: its Physical parent
segment and its logical parent segment.
–Logical twins are occurrences of a logical child segment type that are all subordinates to
a single occurrence of the logical parent segment type.

HOSPITAL

WARD FACILITY

PATIENT NAME

SYMPTOM TREATMNT DOCTOR PBILL BILLING HISTORY

PHYSICAL HOSPITAL DATABASE PHYSICAL HISTORY DATABASE

Figure 8

HOSPITAL
 WARD

PATIENT

BILLING

Figure 9 :- A NEW LOGICAL DATA STRUCTURE

− Note
A new segment type called the PBILL segment is created. Each occurrence of it points to the
appropriate occurrence of the BILLING segment in the HISTORY database.

–A new logical DBD, which maps against two physical DBD'S defining the logical
structure above, is coded.
–PSB'S requiring access to the logical structure above would now reference the logical
DBD rather than either one of the Physical DBD'S
–In Logical Relationships Terminology
–PBILL segment in the HOSPITAL physical database is called a LOGICAL child
segment.
–PATIENT segment for PBILL segment is Physical Parent Segment BILLING segment
in the HISTORY physical database to which PBILL segment is pointing to is called a
Logical Parent Segment.
–This is a Unidirectional Logical Relationship and the advantage is that the BILLING
information exists in only one place in the HISTORY physical database.
–PBILL and BILLING segments are logically related

When a logical child is accessed through its Physical Access path, the destination parent is its
Logical parent. But when it is accessed through its Logical access path, the destination parent
10.16 DBDGEN'S FOR PHYSICAL DATABASE
WITH LOGICAL RELATIONSHIPS
–A logical relationship is implemented by specifying them in the DBDGEN for the
physical database involved.

In the DBD for Hospital Database

SEGM NAME=PBILL
PARENT=((PATIENT, DBLE), (BILLING, HISTDBF))

In the DBD for HISTORY Database

SEGM NAME=BILLING, PARENT=NAME

LCHILD NAME=(PBILL, HOSPDBF)

In the DBD for Logical Database

DBD NAME=HOSPITAL, ACCESS=LOGICAL

DATASET LOGICAL
SEGM NAME=HOSPITAL, PARENT=0,
SOURCE=((HOSPITAL, DATA, HOSPDBD))
SEGM NAME=WARD, PARENT=HOSPITAL
SOURCE=((WARD, DATA, HOSPDBF))
SEGM NAME=PATIENT, PARENT=WARD,
SOURCE=((PATIENT, DATA, HOSPDBD))
SEGM NAME=PBILL, PARENT=PATIENT
SOURCE=((BILLING, DATA, HISTDBF))
DBDGEN
FINISH
END

10.17 PSBGEN USING LOGICAL DATABASE

–There is no difference in setting up the PCB in the PSB for the logical database and
physical database.

PCB TYPE=DB, DBDNAME=HOSPHIST, PROCOPT=A, KEYLEN=

SENSEG NAME=HOSPITAL, PARENT=0
SENSEG NAME=WARD, PARENT=HOSPITAL
SENSEG NAME=PATIENT, PARENT=WARD
SENSEG NAME=PBILL, PARENT=PATIENT
PSBGEN LANG=COBOL, PSBNAME=LOGICPSB
END
10.18 IMS SYSTEM DATASETS
IMSVS.RESLIB This dataset contains all the IMS load modules that make
up the IMS software DB as well as DC. Specified in
STEPLIB or JOBLIB

IMSVS.PGMLIB This dataset contains all the IMS application program load
modules. Specified in STEPLIB or JOBLIB

IMSVS.PSBLIB This dataset contains all the generated PSB'S used by the
application program during execution. Specified in IMS
Ddname.

IMSVS.DBDLIB This dataset contains all the generated DBD'S used by the
application program during execution. Specified in IMS
Ddname.

IMSVS.MACLIB This dataset contains the definitions of the Macros that are
used to generate the PSBGEN and DBDGEN macros.

IMSVS.PROCLIB This dataset contains the IMS catalogued procedures

supplied with IMS

IMSVS.ACBLIB This dataset is used to store the combined PSB'S and

DBD'S information before an application program is
executed. An application program execution JCL must have
access to the IMSVS.RESLIB and IMSVS.DBDLIB
datasets.

When a program is executed, IMS must combine the information in your DBD and PSB
before the execution could begin. To save IMS this trouble each time the program
executes, the DBA may choose to merge the DBD and PSB information ahead of time.
To do this, a procedure called ACBGEN, which stands for Application Control Block
Generation is executed. Once generated, the execution JCL must reference
IMSVS.ACBLIB rather than the PSBLIB and DBDLIB. The use of this dataset is
optional for Batch DL/I programs, but is required for MPP and BMP programs.
 11. APPENDIX - A
11.1 Processing Options - PROCOPT =
G - Get functions GU, GN, GNP, GHU, GHN, GHNP
I - Insert function ISRT
R - Replace function REPL. Also implies G.
D - Deletes function DLET. Also implies G
A - All includes above four functions G, I, R, D
P - Required for Path calls if D command code is to be used in the SSA for the segment.
O - Get calls only, and no Get Hold calls are allowed. If you specify GO or GOP, then
only Get calls like GU, GN, GNP are allowed. If specified for all the PCB'S in the
PSB, then you can execute a DL/I Batch program without making the on-line
Databases off-line.
E - Enqueue the segment or database for on-line program. This facility allows MPP
programs to exclusively use this resource in a Multitasking environment.
L - Load function for database initial loading
GS - Get segments in Ascending Sequence only (HSAM)
LS - Load segments in Ascending Sequence only.
Default - Parameter by Default is a (All)
K - The segment is key sensitive only, cannot access data.
 12. APPENDIX - B
12.1 DL/I STATUS CODES
AB - The call did not specify a segment I-O area (All)
AC - SSA with a hierarchical error. (Get & ISRT)
AH - Call requires atleast one SSA (ISRT)
AI - Error encountered when trying to open the database dataset. An error in the JCL DD
Statement. (All).
AJ - The call specifies an Invalid SSA
AK - The field named in a qualified SSA is not correct (All get calls and ISRT)
AM - Call attempted an unauthorized operation not allowed by the processing options or
Sensitive segments specified in the PCB (all calls)
AO - Call caused an operation resulting in a physical I-O error (All calls)
AT - The I-O area specified in the call is too large, but the program's PSB may be
incorrect. (DLET, REPL and ISRT calls)
DA - The sequence field with key (non-replaceable field) has been changed in the
program's I-O area. (DLET, REPL calls)
DJ - No preceding Get Hold call for a Delete or Replace operation (DLET, REPL calls)
 13. APPENDIX - C
13.1 SYSTEM SERVICE - DL/I CALLS
–There are eight DL/I calls using which IMS performs various system services functions.
–Four important calls are listed below

13.2 CHECKPOINT(CHKP) CALL

–A point in the execution of program when, the changes made to the database are
considered complete and accurate.
–Once checkpointed, the changes made are not reversible.
–By default, the Beginning as well as the normal end of a Batch program are checkpoints.
However, intermediate checkpoints can be established while a program is executing by
issuing a CHKP call.
–CHKP call causes all the databases changes made since the last checkpoint to be
permanently committed to the physical database thereby making a Backout impossible.
–Checkpoint is also known by other similar terms such as synchronization point, commit
point, sync point, integrity point
–A CHKP call causes the database position for a PCB to be reset, apart from releasing all
the locks held by program.
–A CHKP call is of two types. They are

13.3 BASIC CHECKPOINT CALL

–Can be issued by a BATCH and BMP programs
–MPP and Message Driven Fast Path programs must issue only this call
–Apart from committing changes made to the data, it also establishes position in the
program from where to Restart, in case the program abnormally terminates

CALL 'CBLTDLI' USING CHKP

I-O PCB MASK
CHECKPOINT-ID

The I-O PCB must be the first PCB listed on the ENTRY statement normally used for
data communication programs. Checkpoint-ID names a I-O area that contains an Eight-
byte value to identify a checkpoint record written to the log file. During recovery, this
eight byte Checkpoint-ID is used by IMS to Restart the program.
13.4 SYMBOLIC CHECKPOINT CALL
–Can be issued by a BATCH and BMP program
–Apart from committing changes made to the database, it also establishes position in the
program from where to Restart, in case the program abnormally terminates.
–The program can also save as many as SEVEN PAIRS of data area along with the
checkpoint record. These data areas are restored during the program restart.
–A symbolic checkpoint call works with the Extended Restart (XRST) call to restart the
program.

CALL 'CBLTDLI' USING CHKP

I-O PCB MASK
CHECKPOINT-ID
FIRST-AREA-LENGTH
FIRST-IO-AREA
SECOND-AREA-LENGTH
SECOND-IO-AREA
----------
----------
SEVENTH-AREA-LENGTH
SEVENTH-IO-AREA

The I-O PCB mask must be the first PCB listed on the ENTRY statement normally used
for data communication programs having a format different from that of database PCB.
The CheckPoint-ID names a I-O area that contains an Eight-byte value to identify a
checkpoint record written to the log file. Now follows, upto SEVEN PAIRS of field
names defined in the working storage of a program the contents of which is to be saved
along with the checkpoint record. In each pair the first item contains the length of the
datarea to be saved, defined as a Binary field of Full word Type PIC S9 (5) comp, the
second field is the name of the data area storing the contents to be saved. For example

1 FIRST-IO-AREA
05 VALID-TRANS-COUNT PIC S9(5) COMP-3 (3 BYTES)
05 INVALID-TRANS-COUNT PIC S9(5) COMP-3 (3 BYTES)
05 CROSS-SALES-VALUE PIC S9(7) V99 COMP-3 (5 BYTES)
01 FIRST-AREA-LENGTH PIC S9(5) COMP VALUE + 11
13.5 RESTART CALL (XRST)
–The program that issued a symbolic checkpoint CHKP call must issue a restart call
(XRST).
–The XRST call, which is issued only once, does not have to be the first call issued in the
program, though it must be issued before any CHKP call.
–Whether a program is to be restarted or not is determined by DL/I with the help of
PARM parameter specified in the EXEC statement for the program in the execution JCL,
or the CheckPoint ID provided in the Restart Work Area
–If a program is to be Restarted, the XRST call indicates that the following checkpoint
call is a symbolic checkpoint.
–Any calls issued before the XRST call are not within the scope of Restart.

CALL 'CBLTDLI' USING XRST

I-O PCB MASK
Longest Segment Length
Restart-Work-Area
First-Area-Length
First-IO-Area
----------
----------
Seventh-Area-Length
Seventh-IO-Area

The I-O PCB Mask must be the first PCB listed on the ENTRY programs having the
longest segment length is the name of a Full Word Binary field of PIC S9(5) comp that
contains the length of the longest segment area or path of segments the program
processes. DL/I uses this value to acquire the buffer area during a program restart. The
restart work area must be set to BLANKS if the program us not to be Restarted.
However, a Restart is performed when the Restart Work Area is not blanks or the
Checkpoint-ID to be used is provided by the PARM parameter specified in the EXEC
statement for the program in the execution JCL, in which case IMS places the
Checkpoint-ID value in the Restart Work Area automatically. The total number of I-O
areas specified in a call must be less than or equal to the number of areas specified in the
CHKP call and IMS restores only those areas within the program during a program
Restart.
13.6 ROLLBACK CALLS (ROLL AND ROLB)
When issued, will backout all the database updates made by the program since the most
recent Checkpoint. This will nullify the effect of any incorrect processing done by the
program.

ROLL CALL

–When issued, the program is Abnormally Terminated with a user Abend code of 0778
–It also deletes any messages for the program that have been retrieved from the message
queue since the last checkpoint before termination.
–It can be issued in a Batch program

CALL 'CBLTDLI' USING ROLL

The only parameter specified in the call is the function.

ROLB CALL

–Following the call statement for further processing

–It can be issued in a Batch program

CALL 'CBLTDLI' USING ROLB

I-O PCB MASK
DEQ CALL

–When issued, Dequeues all the segments, which have been Enqueued by the call using a
'Q' command, code. Q command code is used to establish an Exclusive control over a
segment by your program preventing others from updating the segment until your
program has released the exclusive control. This will ensure that the segment control will
maintain the same data whenever retrieved by the program till it is released.
–DEQ call may be issued for each class from A thru J
–DEQ call releases all the retrieved segments using the 'E' command code, except those
–Segments modified by the program until the program issues a checkpoint.
–Segments required to keep the position in the hierarchy until the position is
moved to another record.
–Class of segments that has been locked again as another class.

CALL 'CBLTDLI' USING DEQ

I-O PCB MASK
I-O AREA
The I-O area is the name of one byte field that contains a one letter character code from
A thru J. This represents the segments being Dequeued.