COURSE CODE: CSC 315

COURSE TITLE: File Organisation and Data Processing

NUMBER OF Units: 3 Units
Course Duration: Three hours per week

COURSE DETAILS:
Course Lecturers: Dr O. Folorunso and Dr. (Mrs.) O. R. Vincent
Email: folorunsolusegun@yahoo.com, vincent.rebecca@gmail.com
Office Location: Room C and Room B201, COLNAS
Consultation hours: 12-2pm, Wednesdays & Fridays

Course Content: DATA PROCESSING-DATA PROCESSING CYCLE, DATA

PROCESSING METHODS, COMPUTER MODES OF DATA PROCESSING,
DATA VALIDATION TECHNIQUES- BATCH CONTROL, ON-LINE
TRANSACTIONS CONTROL, THE DATA HIERARCHY, FILE PROCESSING
PHYSICAL STORAGE CONSIDERATION- WORSTATIONS AND TERMINALS,

FEATURES OF VDU TERMINALS, OUTPUT DEVICES,

DATA CAPTURE AND DATA ENTRY- FEATURES OF DATA ENTRY,

PROBLEMS OF DATA ENTRY, OPTICAL CHARACTER RECOGNITION (OCR),
OPTICAL MARK READING (OMR)
COMPUTER FILE CONCEPTS,FILE ORGANISATION AND ACCESS

Week One Lecture Note

1.0 DATA PROCESSING

This will discuss data and different validation techniques, for both on-line and batch
systems of data entry. We shall also discuss different file accessing, organization and
processing methods.

DEFINITION OF DATA
Data is the basic fact about an entity. It is unprocessed information. Examples are
a. Student records which contain items like the Student Name, Number, Age, Sex etc
b. Payroll data which contain employee number, name, department, date joined, basic
salary and other allowances
c. Driving License which contain Driver's Name, Date of Birth, Home address, Class
of license and its expiry date
Data can be regarded as the raw material from which information is produced by data
processing. When data is suitably processed, results (or output data) are interpreted to
derive information that would assist in decision- making.

DAT A S T O RAGE U NI T S ON T HE COMP U T E R

Data is stored in the computer in a binary form. The units used to refer to this binary data are
as follows:

Term Definition
Bit The smallest unit of data storage. A bit is either a 1 or a 0.
Nibble 4 bits This term is not commonly used.
i Byte 8 bits. The most commonly used storage unit.
Word This term is architecture dependent. On some systems, a
word is 16 bits; on others, a word is 32 or 64 bits.
Kilobyte (KB) Even though kilo usually means 1,000, a kilobyte in
computer terms is actually 1,024 bytes (because we like
of 2).
Megabyte (MB) _powers
The term megabyte denotes 1,024KB or 1,048,576 bytes.
Gigabyte (GB) i A gigabyte is 1,024 megabytes or 1,073,741,824 bytes.
Terabyte (TB) A terabyte is 1,024 gigabytes or 1,099,511,627,776 bytes.
DATA PROCESSING CYCLE

Data processing may be divided into five separate but related steps. They are

a. Origination
b. Input
c.Manipulatio
d. Output
e. Storage
Origination It should be kept in mind that "to process" means to do something with or
to "manipulate" existing information so that the result is meaningful and can be used by
the organization to make decisions. The existing information is generally original in
nature and may be handwritten or typewritten. Original documents are commonly referred
to as source documents. Examples of source documents are cheques, attendance sheets,
sales orders, invoices, receipts etc. Producing such source documents, then, is the first
step in the data processing cycle.

Input After source documents are originated or made available, the next step is to
introduce the information they contain into the data processing system. This system may
be manual, mechanical, electromechanical or electronic. However, our focus is on
electronic data processing. This is done using any of the available input devices (keyboard,
joystick etc).

Processing When input data is recorded and verified, they are ready to be processed.
Processing or "Manipulation " involves the actual work performed on the source data to
produce meaningful results. This may require performing any or all of the following
functions - classifying, sorting, calculating, recording and summarizing

Output After input data has been fed into a data processing system and properly
processed, the result is called output. Output can be either in summary or detail form. The
type of output desired must be planned in advance so that no waste of time and resources
occur. Included with output is communication. Output is of little value unless it is
communicated properly and effectively. The output is the ultimate goal of data processing.
The system must be capable of producing results quickly, completely and accurately. The
data processing cycle is incomplete without the concept of control. In an organization,
controls depend basically upon the comparison of attained results with predetermined
goals. When the results are compared, they either agree or differ. However, if a
disagreement is detected, a decision is made to make. the necessary changes and the
process repeated. This feedback concept of control is an essential part of data processing.
That is, output is compared with a predetermined standard and a decision is made (if
necessary) on a course of action, and is communicated to the stage where it is taken.

Storage Data related to or resulting from the previous four data processing steps can be
stored, either temporarily or permanently for future reference and usage. It is necessary to
store data, especially when it relates periodic reports, since they are used over and over
again in other related applications.

A monthly attendance report or profit and loss statements will be useful in preparing
annual reports. Stored information can either be raw, semi-processed or output data. Quite
often, the output of one problem becomes the input to another. In the case of inventory,
any unsold at the end of a year (ending inventory) become the beginning inventory for the
next year. There are various ways of storing data, ranging from simple recording to
storage in diskettes, hard disks, CDs etc.

DATA PROCESSING METHODS

Data originates in many different forms and they are many methods of processing:-
manual, mechanical and electronic. The method used, however depends on its suitability to
the task at hand. There are some that are best suited for electronic processing, while
others are better done by manual methods.

Manual Method
This involves preparing data by means of such tools as pens, pencils, ledgers, files, folders
etc. Improvements on these include using multi-copy forms, carbon paper etc. A good
example is the daily marking of attendance register in school.

Advantages
a. They are generally cheap
b. Simple to operate
c. Easily adaptable to
changes d. Easily accessible

Disadvantages

a. May take long time to complete

b. Cannot handle large of volume of work
easily c. Generally prone to errors
d. Waste a lot of manpower

Mechanical Method
This method involves the use of a combination of manual processes and mechanical
equipment to carry out the function. Examples are Typewriters, Calculators etc.

Advantages
a. Widely used in large and small organizations
b. Can serve as input to electronic system
c. Quality and level of output greatly improved as compared to manual method
d. Requires less manpower than the manual method

Disadvantages
a. Costly to purchase and maintain
b. Possibility of equipment breakdown
c. Produces lots of noise due to moving parts in the equipment
d. Usually slow in operation

Electronic Method
Here, the processing is done electronically by the system. There are two modes; batch
processing and on-line processing.

Advantages
a. Faster analysis and results of processing
b. Handles complex calculations and problems
c. Can provide information in different and varied formats
d. Provides more accurate results than the other two methods
e. Work load capacity can be increased easily without
hitches f. Provides for standardization of method g. Frees
staff from clerical tasks for other tasks e.g. planning

Disadvantages
a. Initial acquisition cost may be high as well as maintenance
costs b. Specialist personnel may be required
c. Decreased flexibility as tasks become standards

COMPUTER MODES OF DATA PROCESSING

There are two modes of computer data processing; Batch Processing and On-line
Processing.

Batch Processing
A method of processing information in which transactions are accumulated and stored until a
specified time when it is necessary or convenient to process them as a group. This method
is usually adopted in payroll processing and sales ledger updates.

On-line Processing
A method of processing information in which, transactions are entered directly into the
computer and processed immediately. The on-line method can take different forms. These
forms are examined below.

Real Time Processing This is an on-line processing technique in which a transaction

undergoes all the data processing stages immediately on data capture. This method is
used in Airline ticket reservation and modern retail banking software.
Multiprogramming - This method permits multiple programs to share a computer
system's resources at any one time through the concurrent use of the CPU. By concurrent
use, we mean that only one program is actually using the CPU at any given moment, but
that the
input/output needs of other programs can be serviced at the same time. Two or more
programs are active at the same time, but they do not use the same computer resources
simultaneously. With multiprogramming, a set of programs takes turns using the
processor.

Multitasking - This refers to multiprogramming on single-user operating system such as

those in microcomputers. One person can run two or more programs concurrently on a
single computer. For example, the user can be working on a word-processing program and at
the same time be doing a search on a database of clients. Instead of terminating the
session with the word processing program, returning to the operating system, and then
initiating a session with the database program, multitasking allows the display of both
programs on the computer screen and allows the user to work with them at the same time.

Time Sharing - This capability allows many users to share computer-processing resources
simultaneously. It differs from multiprogramming in that the CPU spends a fixed amount of
time on one program before moving on to another. In a time-sharing environment, the
different users are each allocated a tiny slice of computer time. In this time slot, each user is
free to perform any required operations; at the end of the period, another user is given a
time slice of the CPU. This arrangement permits many users to be connected to a CPU
simultaneously, with each receiving only a tiny amount of CPU time. Time-sharing is also
known as interactive processing. This enables many users to gain an on-line access to the
CPU at the same time, while the CPU allocates time to each user, as if he is the only one
using the computer.

Virtual Storage - Virtual storage was developed after some problems of multiprogramming
became apparent. It handles programs more efficiently because the computer divides the
programs into small fixed or variable length portions, storing only a small portion of the
program in primary memory at one time, due to memory size constraints as compared
program needs. Virtual storage breaks a program into a number of fixed-length portions
called pages or variable length portions called segments. The programmer or the operating
system determines the actual breakpoint between pages and segments. All other program
pages are stored on a disk unit until they are ready for execution and then loaded into
primary memory. Virtual storage has a number of advantages. First, primary storage is
utilized more fully. Many more programs can be in primary storage because only one
page of each program actually resides there. Secondly, programmers need not worry
about the size of the primary storage area. With virtual storage, there is no limit to a
program's storage requirements

Week Two Lecture Note

DATA VALIDATION TECHNIQUES

GIGO stands for Garbage-In, Garbage-Out. This means that whatever data you pass or enter

-7-
into the computer system is what would be processed. The computer is a machine and
therefore has no means of knowing whether the data
supplied is the right one or not. To minimize such situations that may lead to the
computer processing wrong data and producing erroneous output, data entered into a
computer is validated within specific criteria to check for correctness before being
processed by the system. This process is called DATA VALIDATION. We stated above
that computer data processing is done in batch and on-line processing modes and we shall
therefore discuss data validation techniques under each of these two modes.

Batch Control

This type of input control requires the counting of transactions or any selected quantity
field in a batch of transactions prior to processing for comparison and reconciliation after
processing. Also, all input forms should be clearly identified with the appropriate
application name and transaction type (e.g. Deposits, Withdrawals etc). In addition, pre-
numbered and pre-printed forms can be used where constant data are already printed and
used to reduce data entry or recording errors.

Types of Batch Controls include:

 Total Monetary Amount - This is used to verify that the total monetary value of
items processed equals the total monetary value of the batch documents.
 Total Items - This verifies that the total number of items included on each
document in the batch agrees to the total number of items processed. For example,
the total number of items in the batch must equal the total number of items
processed.
 Total Documents - This verifies that the total number of documents in the batch
equals the total number of documents processed. For example, the total number of
invoices agrees with the number of invoices processed.
 Hash Total - Hashing is the process of assigning a value to represent some original
data string. The value is known as hash total. Hashing provides an efficient method
of checking the validity of data by removing the need for the system to compare
the actual data, but instead allowing them to compare the value of the hash, known
as the hash total, to determine if the data is same or different. For example, totals
are obtained on an identifier (meaningless) data fields such as account number,
part number or employee number. These totals have no significance other than
for internal system control purposes. The hash total is entered at the start of the
input process; after completion, the system re-calculates this hash total using the
selected fields (e.g. account number) and compares the entered and calculated hash
total. If the same, the batch is accepted or otherwise rejected.

On-Line Transactions Control

An advantage of on-line real time systems is that data editing and validation can be done
up front, before any processing occurs. As each transaction is input and entered it can be
operator prompted immediately an error is found and the system can be
designed to reject additional input until the error is corrected. The most important data edit
and validation techniques are discussed below, but the list is by no means exhaustive.

 Reasonableness Check - Data must fall within certain limits set in advance or they
will be rejected. For example, If an order transaction is for 20,000 units and normally
not more than 100 units, then the transaction will be rejected.
 Range Check - Data must fall within a predetermined range of values. For
example, if a human weighs more 150kg, the data would be rejected for further
verification and authorization.
 Existence Check - Data are entered correctly and agree with valid predetermined
criteria. For example, the computer compares input reference data like Product type to
tables or master files to make sure the codes are valid.
 Check Digit - An extra reference number called a check digit follows an
identification code and bears a mathematical relationship to the other digits. This
extra digit is input with the data, recomputed by the computer and the result
compared with the one entered.
 Completeness Check - A field should always contain data and riot zeros or blanks. A
check of the field is performed to ensure that some form of data, not blanks or
zeros is present. For example, employee number should not be left blank as it
identifies that employee in the employee record.
 Validity Check - This is the programmed checking of data validity in accordance with
predetermined criteria. For example, a gender field should contain only M(ale) or
F(emale). Any other entry should be rejected.
 Table Lookups - Input data complies with predetermined criteria maintained in a
computerized table of values. For example, a table maintains the code for each local
government in the country and any number entered must correspond to codes
found in the table.
 Key Verification - another individual using a program that compares the original
entry to the repeated keyed input repeats the key-in process. For example, the
account number, date and amount on a cheque is keyed in twice and compared to
verify the keying process.
 Duplicate Check - New transactions are matched to those previously entered. For
example, an invoice number is checked to ensure that it is not the same as those
previously entered, so that payment is made twice.
 Logical Relationship Check - If a particular condition is true, then one or more
additional conditions or data input relationship might be required to be true before
the input can be considered valid. For example, an employee applying to be paid
maternity leave allowance or employment date may be required to be at least
eighteen years from date of birth and be a Male employee.

The Data Hierarchy

A computer system organizes data in a hierarchy that starts with bits and bytes
and progresses to fields, records, files, and databases.
A bit represents the smallest unit of data a computer can handle. A group of bits,
called a byte, represents a single character, which can be a letter, number or other
symbol. A grouping of characters into a word, group of words or a complete number
(e.g. a person's first name or age), is called a field. A group of related fields, such as
a student's name, class, date admitted, age make up a record.
A group of records of the same type (e.g. the records of all students in the class) is
called a file. A group of related files (e.g. the personal history, examinations records
and payments history files) make up a database.

A record describes an entity. An entity is a person, place, thing, or event on which

we maintain information. An employee record is an entity in a personnel records
file and maintains information on the employees in that organization. Each
characteristic or quality describing a particular entity is called an attribute. For
example, employee name, address, age, gender, date employed is an attribute each of
the entity personnel. The specific values that these attributes can have can be
found in the field of the record describing the entity.

Every record in the file contains at least one field that uniquely identifies that record
so that the record can be retrieved, changed, modified or sorted. This identifier is
called the key field. An example of a key field is the employee number for a
personnel record containing employee data such as name, address, age, job title etc.

File Accessing Methods

Computer systems store files in secondary storage (e.g. hard disks) devices. The
records can be arranged in several ways on the storage media, and the arrangement
determines the manner in which the individual records can be accessed or retrieved.

Sequential Access File Organization - In sequential file organization, data records

must be retrieved in the same physical sequence in which they are stored.
Sequential file organization is the only method that can be used on magnetic
tape.(e.g. data or audio tape). This method is used when large volumes of records
are involved and it is suitable for batch -processing as it is slow.

Direct/Random Access File Organization - This is a method of storing records so that

they accessed in any sequence without regard to their actual physical order on the
storage media. This method permits data to be read from and written back to, the
same location. The physical location of the record in the file can be computed from
the record key and the
 physical address of the first record in the file, using a transform algorithm, not an index.
(The transform algorithm is a mathematical formula used to translate the key field directly
into the record's physical location on disk.) Random access file organization is good for
large files when the volume of transactions to be processed against the file is low. It is used to
identify and update an individual's record on a real-time basis. It is fast and suitable for on-
line processing where many searches for data are required. It is faster than sequential file
access method. An example is an on-line hotel reservation system.

Index Sequential Access Method - This file access method directly accesses records
organized sequentially using an index of key fields. An index to a file is similar to the
index of a book, as it lists the key fields of each record and where that record is physically
located in storage to ensure speedy location of that record. ISAM is employed in
applications that require sequential processing of large numbers of records but
occasionally require direct access of individual records. An example is in airline
reservation systems where booking can be taking place in different parts of the world at the
same time accessing information from one file. ISAM allows access to record in the most
efficient manner.

Flat File - Supports a batch-processed file where each record contains the same type of data
elements in the same order, with each data element needing the same number of storage
spaces. Supports a few users' needs. It is inflexible to changes. It is used to enter data into
an application automatically in a batch mode, instead of record by record. This process of
automatic batch data entry is also referred to as a File Upload process.

Database File - A database supports multiple- users needs. The records are related to each
other differently for each file structure. Removes the disadvantages of flat files.

Object Oriented File Access - Here, the application program accesses data objects and uses a
separate method to translate to and from the physical format of the object.

File Processing
I Different processes can be performed on files stored in the computer system. These
processes include:

 Updating - The process of bringing information contained in the file up to date by

feeding in current information
 Sorting - Arranging the records in a file in a particular order (e.g. in alphabetical or
numerical order within a specified field)
 Merging - Appending or integrating two or more files into a bigger file
 Blocking - This is to logically arrange the records in a file into fixed or variable
blocks or sets that can be treated as a single record at a time during processing. The
gap between each block is known as the inter-block gap.
• Searching - This involves going through a whole file to locate a particular record or a set of
records, using the key field.
 Matching - This involves going through a whole file to locate a particular record or a set
of records, using one or a combination of the file attributes or fields.
Week Three Lecture Note

Physical storage consideration

"Volume" is a general term for any individual physical storage medium that can be written to or
read from. Examples include: a fixed hard disk, a disk pack, a floppy disk, a CD-ROM, a disk
cartridge or a tape cartridge.
Initialization. Before a disk may be recorded upon it normally has to be initialized which
involves writing zeroes to every data byte on every track. A special program is normally
supplied for this purpose. Clearly, the re-initialization of a disk effectively eliminates all trace
of any existing data.
Formatting. In addition to Initialization the disk has to be formatted which means that a
regular pattern of blank sectors is written onto the tracks. In the case of floppy disks the
"formatting" program normally combines formatting with Initialization. On magnetic tapes
the format is defined when the tape is mounted on the drive. Blocks of data are then
formatted as they are written to the tape. The format determines the effective storage
capacity of the volume. For example, a double sided floppy disk with 80 tracks per side and 9
sectors per track with each sector containing 512 data bytes will have a storage capacity of 720
Kbytes (ie, 9 x 40 x 2 x 512 bytes). Formats depend upon the manufacturer and operating system
used. If data is to he transferred from one computer to another not only must the volume be
physically interchangeable between drives the volume format must be compatible