Introduction to DB Transparencies

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Chapter 1

Introduction to Databases

Transparencies


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Chapter 1 Objectives

u Some common uses of database systems.

u The characteristics of file-based systems.

u The problems with the file-based approach.

u The meaning of the term database.


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u The meaning of the term Database

Management System (DBMS).

u The typical functions of a DBMS.

u The major components of the DBMS

environment.

u The personnel involved in the DBMS

environment.


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u The history of the development of DBMSs.

u The advantages and disadvantages of DBMSs.


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File-based Systems

u A collection of application programs thatperform services for the end users (e.g.reports).

u Each program defines and manages itsown data.


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File-based Processing


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Limitations of File-based Approach

u Separation and isolation of data

Each program maintains its own set ofdata. Users of one program may be

unaware of potentially useful data held byother programs.

u

Duplication of data Same data is held by different programs.

Wasted space and potentially differentvalues and/or different formats for the

same item.


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u Data dependence

File structure is defined in the programcode.

u Incompatible file formats

Programs are written in different

languages, and so cannot easily accesseach others files.


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u Fixed Queries/Proliferation of applicationprograms

Programs are written to satisfy

particular functions. Any newrequirement needs a new program.


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Database Approach

u Arose because:

Definition of data was embedded inapplication programs, rather than being

stored separately and independently.

No control over access andmanipulation of data beyond that

imposed by application programs.

u Result - the database and DatabaseManagement System (DBMS).


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Database

u A shared collection of logically related data(and a description of this data), designed tomeet the information needs of an organization.

u System catalog (data dictionary or metadata)provides the description of the data to enableprogramdata independence.

u Logically related data comprises entities,attributes, and relationships of an

organization's information.


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Database Management System (DBMS)

u A software system that enables users todefine, create, and maintain the databaseand which provides controlled access to

this database.


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Database Management System (DBMS)


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Database Approach

u Data definition language (DDL).

Permits specification of data types,structures and any data constraints. All

specifications are stored in thedatabase.

u Data manipulation language (DML). General enquiry facility (query

language) of the data.


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Database Approach

u Controlled access to database mayinclude:

A security system.

An integrity system.

A concurrency control system.

A recovery control system.

A user-accessible catalog.

u A view mechanism.

Provides users with only the data theywant or need to use.


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Components of DBMS Environment


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u Hardware

Can range from a PC to a network ofcomputers.

u Software

DBMS, operating system, network software(if necessary) and also the applicationprograms.

u Data

Used by the organization and adescription of this data called the

schema.


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u Procedures

Instructions and rules that should beapplied to the design and use of the

database and DBMS.u People


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Roles in the Database Environment

u Data Administrator (DA)

u Database Administrator (DBA)

u Database Designers (Logical andPhysical)

u Application Programmers

u End Users (native and sophisticated)


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History of Database Systems

u First-generation

Hierarchical and Network

u Second generation

Relational

u Third generation

Extended Relational

Object-Oriented


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Advantages of DBMS

u Control of data redundancy.

u Data consistency

u More information from the same amountof data.

u Sharing of data.

u Improved data integrity.

u Improved security.

u Enforcement of standards.

u Economy of scale.


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Advantages of DBMS

u Balanced conflicting requirements

u Improved data accessibility andresponsiveness

u Increased productivity

u Improved maintenance through dataindependence

u Increased concurrencyu Improved backup and recovery services


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Disadvantages of DBMS

u Complexity

u Size

u Cost of DBMS

u Additional hardware costs

u Cost of conversion

u Performance

u Higher impact of a failure

Introduction to DB Transparencies

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