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II: Overview

Well discuss:

What a database is, what it does, andwhy database design is important

What a DBMS is, what it does, and how

it fits into the database system Database Architecture and

structural/data independence

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Database Management

Database is shared, integratedcomputer structure housing: End user data

Metadata

Database Management System(DBMS)

Manages Database structure Controls access to data

Contains query language

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Importance of DBMS

Makes data management more efficient andeffective

Query language allows quick answers to ad

hoc queries Provides better access to more and better-

managed data

Promotes integrated view of organizations

operations Reduces the probability of inconsistent data

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DBMS Functions

Data dictionary management

Data storage management

Data transformation and

presentation Security management

Multiuser access control

Backup and recovery

management Data integrity management

Database language andapplication programminginterfaces

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Working on application logic does not require the knowledgeof underlying data organization and access path structure ofthe data.

Structural and Data

Independence

The user is allowed to retrieve and manipulate data based

on his/her knowledge about data at the logical level ratherthan lower level data representation.

Modification made in the access path structure and physicalstorage structure should not affect the application

programs. Database growth does not affect the application

programs.

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Database Models

Collection of logical constructsused to represent data structure

and relationships within thedatabase

Conceptual models: logical nature of

data representation Implementation models: emphasis on

how the data are represented in thedatabase

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Relationships in Conceptual Models

One-to-one (1:1)

One-to-many (1:M) Many-to-many (M:N)

Implementation Database Models

Hierarchical

Network

Relational

Object-oriented

Database Models (cont.)

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Hierarchical Database Model

Logically represented by an upsidedown tree

Each parent can have many children

Each child has only one parent

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Hierarchical Database Model

Advantages Conceptual simplicity

Database security and integrity

Data independence Efficiency

Disadvantages Complex implementation

Difficult to manage and lack of standards Lacks structural independence

Applications programming and usecomplexity

Implementation limitations

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Network Database Model Each record can have multiple parents

Composed of sets

Each set has owner record and memberrecord

Member may have several owners

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Network Database Model

Advantages

Conceptual simplicity

Handles more relationship types

Data access flexibility Promotes database integrity

Data independence

Conformance to standards

Disadvantages

System complexity

Lack of structural independence

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Relational Database Model

Perceived by user as a collectionof tables for data storage

Tables are a series of row/columnintersections

Tables related by sharing commonentity characteristic(s)

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Relational Database Model(cont.)

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Relational Database Model

Advantages

Structural independence

Improved conceptual simplicity Easier database design,

implementation, management, anduse

Ad hoc query capability with SQL

Powerful database managementsystem

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Relational Database Model

Disadvantages

Substantial hardware and systemsoftware overhead

Poor design and implementation ismade easy

islands of information problems

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Entity Relationship DatabaseModel

Complements the relational data modelconcepts

Represented in an entity relationshipdiagram (ERD)

Based on entities, attributes, andrelationships

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Entity Relationship Database

Model Advantages Exceptional conceptual simplicity

Visual representation

Effective communication tool Integrated with the relational database

model

Disadvantages

Limited constraint representation Limited relationship representation

No data manipulation language

Loss of information content

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Object-Oriented Database

Model Objects or abstractions of real-world entities are stored

Attributes describe properties

Collection of similar objects is a class

Methods represent real world actions ofclasses

Classes are organized in a class hierarchy Inheritance is ability of object to

inherit attributes and methods ofclasses above it

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OO Data Model

Advantages

Adds semantic content

Visual presentation includes semanticcontent

Database integrity

Both structural and data independence

Disadvantages

Lack of OODM Complex navigational data access

Steep learning curve

High system overhead slows transactions

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Database Models and theInternet

Characteristics of Internet agedatabases

Flexible, efficient, and secure Internet

access Easily used, developed, and supported

Supports complex data types andrelationships

Seamless interfaces with multiple datasources and structures

Simplicity of conceptual database model

Many database design, implementation,

and application development tools