Download - Lec-1 Introduction to Databases

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DATABASE MANAGEMENT SYSTEMS (BIS3103)

Lecturer: Alice Nandawula Mugisha

Email: [email protected]

Room: Room 202 (Staff Working Space), Block A

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mailto:[email protected]:[email protected]


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CHAPTER 1Introduction to Databases2


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OBJECTIVES

Characteristics of file-based systems.

Problems with file-based approach.

Meaning of the term database.

Meaning of the term Database Management System

(DBMS).

Typical functions of a DBMS.

Advantages and disadvantages of DBMSs.

Some common uses of database systems

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FILE-BASED SYSTEMS

A file is a collection of records which

contain logically related data.Collection of application programs that

perform services for the end users (e.g.

reports).

Each program defines and manages its own

data.

Better alternative to paper based filing

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FILE-BASED APPROACH

A system of files and collection of applicationprograms manipulating them is a file-basedsystem

The UniversitysFile-Based System


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LIMITATIONS OF FILE-BASED APPROACH

Separation and isolation of data

Each program maintains its own set of data.

Users of one program may be unaware of

potentially useful data held by other programs.

Duplication of data

Same data is held by different programs.

Wasted space and potentially different values and/ordifferent formats for the same item.

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LIMITATIONS OF FILE-BASED

APPROACH

Data dependence

Unhealthy dependency between data and programs.Filestructure is defined in the program code.

Incompatible file formats Programs are written in different languages, and so

cannot easily access each others files.

Fixed Queries/Proliferation of application programs

Programs are written to satisfy particular functions. Anynew requirement needs a new program.

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DATABASE APPROACH

Arose because:

Definition of data was embedded inapplication programs, rather than beingstored separately and independently.

No control over access and manipulationof data beyond that imposed byapplication programs.

Therefore there was a need to

separate data from programs but witha facility for them to interact.

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DATABASE APPROACH

Result

the database and Database ManagementSystem (DBMS).

Databases were therefore developed tostore, organize and secure data whileapplications can be able to access thedatabase, process the data and generatethe required information. 9


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DATABASE

Shared collection of logically related data (and adescription of this data), designed to meet theinformation needs of an organization.

System catalog (metadata) provides description ofdata to enable programdata independence.

Logically related data comprises entities,attributes, and relationships of an organization'sinformation.

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DATABASE APPROACH

Data definition language (DDL).

Permits specification of data types, structures and anydata constraints that should be part of the database.

All specifications are stored in the database.

Data manipulation language (DML). Enables those with access to the database to insert,

update, delete and retrieve data from it.

Standard Query Language (SQL) is an example of a

DML

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DATABASE ENVIRONMENT PLAYERS

Data Administrator: Responsible over the data policies in

the organization. Does not need to be a technical person. Database Administrator: Puts into practice the data

policies of the organization, like back ups, recovery,

integrity, security, availability, performance and testing

support.

Applications Program Developer: Responsible over

development of the application programs that make use of

the data in the database.

User: Makes use of the information from the applications

that talk to the database. The user may be novice or

sophisticated

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DATABASE MANAGEMENT SYSTEM

(DBMS)

DBMS: A software system that enables

users to define, create, and maintain the

database and which provides controlled

access to this database.

Database Application: A computer programthat interacts with the database by issuing an

appropriate request (typically an SQLstatement) to the DBMS.

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FUNCTIONS OF A DBMS

Authorization Services.

Support for Data Communication.

Integrity Services.

Services to Promote Data Independence.

Utility Services.

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ADVANTAGES OF DBMS

Control of data redundancy

Data consistency

More information from the same amount of data.

Sharing of data Improved data integrity

Improved security

Enforcement of standards

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ADVANTAGES OF DBMS

Balanced conflicting requirements

Improved data accessibility and responsiveness

Increased productivity

Improved maintenance through data independence Increased concurrency

Improved backup and recovery services

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DISADVANTAGES OF DBMS

Complexity

Size

Cost of DBMS

Additional hardware costs Cost of conversion

Performance

Higher impact of a failure

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DATA BASE MODELS

A database model is an organizational principleused in organizing data by a databasemanagement system.

Different database management systems of thesame model have the same principle of dataorganization. e.g. MS Access, Oracle and MicrosoftSQL server use tables (relations) to organize thedata.

They are 'Relational' database managementsystems.

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TYPES OF DATABASE MODELS The Network Model: Represents data as nodes and

relationships are implied by linking up the nodes by

edges. The Hierarchical Model: Represents data and nodes

in a hierarchical manner.

The Deductive Model: Represents minimal data as'Axioms'. Extra data and relationships are deduced.

The Relational Model: Uses relations/table toorganize data. A row/tuple represents an instance ofdata and relationships are represented by foreignkeys.

The Object Oriented Model: Uses the objectoriented paradigm of encapsulation, inheritance andpolymorphism. A class represents data and an objectrepresents the instance.

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