INTRODUCTION TO DBMS

Contents

 Definition of data, information, knowledge

 Definition of database, DBMS
 Database vs. File systems.
 Three-schema architecture
 Data independence
 Database users
 Database Administrator(DBA)
Definition of Data & information

 What is data?

Known facts that

can be recorded
and have some
implicit meaning

 What is information?
Meaningful data
 Definition of knowledge

 What is knowledge?

 knowledge indicates the information which not only

utilize in current decision making but also store for later
use.

 What is the difference between knowledge and

information?
 Definition of Database, DBMS

 What is database?

 organized collection of related information presented to

serve a specific purpose

 What is database management system (DBMS)?

 a collection of interrelated data (database)

and
 a set of programs to access those data and maintain
database concurrently and efficiently.
 Purpose of Database Systems
Limitations of File Systems
 In the early days, database applications were built on top of file
systems
 Data is stored in separate files
 Data is manipulated by a set of application programs

 As time goes by, the number of files and application programs

increases
 increasing complexity of database application management
 Purpose of Database Systems
Limitations of File Systems
 Drawbacks of using file systems to store data
 Data redundancy and inconsistency
 Redundancy: duplication of information in different files
 Inconsistency: the various copies of the same data may be different

 Difficulty in accessing data

 Need to write a new program to carry out each new task

 Data isolation — multiple files and formats

 Because data are scattered in various files, and files may be in different formats,
writing the appropriate information to retrieve the appropriate data is difficult

 Integrity problems
 Data values stored in the database must satisfy certain types of consistency
constraints
 Integrity constraints (e.g. account balance > 0) become part of program code
 Those constraints are forced by the database system developer
 Hard to add new constraints or change existing ones
 Purpose of Database Systems
Limitations of File Systems
 Atomicity of updates

 Failures may leave database in an inconsistent state with partial updates

carried out
 E.g. transfer of funds from one account to another should either complete or
not happen at all

 Concurrent access by multiple users

 Concurrent accessed needed for performance
 Uncontrolled concurrent accesses can lead to inconsistencies
 E.g. two people reading a balance and updating it at the same time

 Security problems
 Not every user of the database should be able to access all the data

Database systems offer solutions to all previous problems

 Schema & Instance
 Instance: The collection of information stored in the
database in a particular moment is called instance of
database.

 Schema: The overall design of the data base is schema.

 Difference between them:

Instance of a database changes over time as information is
inserted and deleted. Schema changes infrequently.
 View of Data in a Database
The Need for Data Abstraction
 A major purpose of a database system is to provide users with an
abstract view of data
 The system hides certain details of how the data are stored and
maintained

 The objective of data abstraction is to simplify the interaction with

the database from the user perspective
 Most of database users are not computer trained

 However, more complexity from the design perspective

 Complex data structure to represent data
 View of Data in a Database
The levels of Data Abstraction

Physical Level: describes how

the data is actually stored

 Describes low level data

structures.
What to store
 Block of consecutive storage
locations (e.g. bytes)
How to store
 The compiler hides this level
of details from programmers.
 View of Data in a Database
The levels of Data Abstraction
Logical Level: describes what type customer =
data are stored in the database record
name: string;
and what relationships exist street: string;
city: integer;
between data end;

 each record is described by a type definition

 Programmers work at this level of abstraction
 Similar to database administrator

 .
 View of Data in a Database
The levels of Data Abstraction

View Level: describes only part of the entire database.

 application programs hide details of data types.

 Views can also hide information (e.g. salary) for security purposes.
 computer users only see a set of applications without details on data
types
 Similar to users of database
 Data Abstraction

Each layer need not know how other layers organize data.
 Mapping
 Mappings among schema levels are needed to transform
requests and data.

 Programs refer to an external schema, and are mapped by

the DBMS to the internal schema for execution.

Request for a data

External level

Request against a conceptual schema

Conceptual level

Request against internal schema

Internal level
 Data Independence

• Logical Data Independence: The capacity to change the

conceptual schema without having to change the external
schemas and their application programs.

• Physical Data Independence: The capacity to change the

internal schema without having to change the conceptual
schema.
 Database Users

Users are differentiated by the way they expect to interact

with the system :

 those who actually use and control the content (called

“Actors on the Scene”)
and

 those who enable the database to be developed and the

DBMS software to be designed and implemented (called
“Workers Behind the Scene”).
 Database Users
 Database administrators: responsible for authorizing access
to the database, for coordinating and monitoring its use, acquiring
software, and hardware resources, controlling its use and
monitoring efficiency of operations.

 Database Designers: responsible to define the content, the

structure, the constraints, and functions or transactions against the
database. They must communicate with the end-users and
understand their needs.

 End-users: they use the data for queries, reports and some of
them actually update the database content.

 Application Programmers: System analysts determine the

requirements of end-users and programmers implement programs,
test, debug and document.
 Database End-Users

1. Casual : access database occasionally when needed

2. Naïve or Parametric : invoke one of the permanent application

programs that have been written previously
 E.g. Bank cashier, people accessing a database over the web
 The typical user interface for naïve user is a form interface
where the user just fill in the appropriate fields of the form
 Database End-Users

3. Sophisticated : these include business analysts, scientists,

engineers, others thoroughly familiar with the system capabilities.
Many use tools in the form of software packages that work closely
with the stored database.

4. Stand-alone : mostly maintain personal databases using ready-to-

use packaged applications. An example is a tax program user that
creates his or her own internal database.
 Database Administrators

 The Database Administrator (DBA) Coordinates all the activities of the

database system

 The DBA has a good understanding of the enterprise’s information resources

and needs

 The DBA has central control over the system

 Database Administrators

 Database administrator's duties include:

 Schema definition, specifying integrity constraints
 Storage structure and access method definition
 Schema and physical organization modification
 Granting user authority to access the database
 Acting as liaison with users
 Monitoring performance and responding to changes in
requirements
 Routine maintenance (DB backup, Ensuring free space for the DB,
etc …)
 Transaction management

 A transaction is a collection of operations that performs a single

logical function in a database application

 Transaction-management component ensures that the database

remains in a consistent (correct) state despite system failures (e.g.,
power failures and operating system crashes) and transaction failures.

 Concurrency-control manager controls the interaction among the

concurrent transactions, to ensure the consistency of the database.
 Storage Management

 Storage manager is a program module that provides the interface

between the low-level data stored in the database and the application
programs and queries submitted to the system.

 The storage manager is responsible to the following tasks:

 interaction with the file manager
 efficient storing, retrieving and updating of data
 Data dictionary

• Used to store schema descriptions and other information such as

data about data (metadata), design decisions, application
program descriptions, user information, usage standards, etc.

• Active data dictionary is accessed by DBMS software and

users/DBA.

• Passive data dictionary is accessed by users/DBA only.

 Data dictionary

A data dictionary should help a user in:

 Communication with the users

 Controlling data element in a simple and effective
manner
 Determining the impact of changes to data element on
the total database
 Centralizing the control of a data element.
 Database System Applications

 Banking: all transactions

 Airlines: reservations, schedules
 Universities: registration, grades, student information
 Sales: customers, products, purchases
 Manufacturing: production, inventory, orders, supply chain
 Human resources: employee records, salaries, tax deductions
 Telecommunications: keeping record of calls made, generating
monthly bills
 Architecture

catalog

Databases are self-describing: catalog describes

the structure of the data stored in the DB
 Client-server Architecture

Two-tier architecture: E.g. client programs using ODBC/JDBC to

communicate with a database
Three-tier architecture: E.g. web-based applications, and
applications built using “middleware”