Lecture 1b - Database Models

8/6/2019 Lecture 1b - Database Models

1/33

Lecture 1bData Models

Reference Textbook: An Introduction to Database

Systems

Eighth Edition

C.J.Date


2/33

2

Lecture 1b Overview

Definitions

Evolution of Data Models


3/33

3

Data Models

Data modelis an abstract model that describes how data isrepresented and used

ORData modelis a collection of logical constructs used to represent the

data structure and the data relationships found within the database.

Two Categories of Database Models:

Logical or Conceptual models focus on the logical nature of the

data representation. They are concerned with whatisrepresented rather than howit is represented.

Physical or Implementation models place the emphasis onhowthe data are represented in the database or on howthe datastructures are implemented.


4/33

4

Data Models

Numerous logical data models have been proposed,under two main groups:

- Object-based models

entity-relationship, object-oriented, semantic,functional, ...

- Record based models

relational, network, hierarchical, ...


5/33

5

The Evolution of Data Models


6/33

6

The Hierarchical ModelEvolution

Developed in the 1960s to manage large

amounts of data for manufacturing projects

Information Management System (IMS)

Worlds leading mainframe hierarchical database

system in the 1970s and early 1980s


7/33

7

Hierarchical Structure-Characteristics

Logically represented by an upside down tree

Each parentcan have many children Each childhas only one parent

Tree is defined by path that traces parent segments to

child segments, beginning from the left

Hierarchical path Ordered sequencing of segments tracing hierarchical structure

Preorder traversal or hierarchic sequence Left-list path


8/33


9/33

9

Customer ata

Name ddress Phone Pointer toChecking

cct. ata

Pointer to uto

Loan ata

Maria Chavez 1441 damsCourt 605-777-8992John everson 8988 Grover oad 605-898-2314Harold Brown 3511 Pluto rive 605-666-3298

Checking ccount ata

cct. Number Current Balance ate LastTransaction

986-335 445.11 07/11/03

988-310 2988.44 07/01/03355-822 898.14 06/15/03

uto Loan ata

cct. Number Current Balance ate Last Pmt

100988 5676 06/15/03

101732 1545.33 07/01/03

Hierarchical DatabasesHierarchical Databases


10/33

10

Hierarchical Model

Foundation for current data models

Advantages Conceptual simplicity

Database security and integrity

Data independence

Efficiency

Disadvantages Complex implementation

Difficult to manage

Lack of standards

Lacks structural independence

Relationships do not conform to 1:M form

No standards for how to implement


11/33

11

Child with Multiple Parents


12/33

12

Network Model

Created to represent complex data relationships more effectively

Improve database performance

Impose a database standard

Resembles hierarchical model

Record may have more than one parent

Collection of records in 1:M relationships

Each record can have multiple parents

Composed of sets

Each set has owner record and member record

Member may have several owners


13/33

13

ANetwork Data Model


14/33

14

Network Data Model

Advantages Conceptual simplicity

H

andles more relationship types Data access flexibility

Promotes database integrity

Data independence

Conformance to standards

Disadvantages System complexity Lack of ad hoc query capability placed burden on programmers to

generate code for reports

Structural change in the database could produce havoc in allapplication programs


15/33

15

Relational Model

Developed byCodd (IBM) in 1970

Considered ingenious but impractical in 197

0 Conceptually simple

Computers lacked power to implement the relational model

Today, microcomputers can run sophisticated relational

database software


16/33

16

Relational database is perceived as collection of tables.

Each table consists of series of row/column intersections.

Tables (or relations) are related to each other by sharing acommon entity characteristic.

Relationship type is often shown in a relational schema.

Table yields complete data and structural independence.

Relational Data Models Basic StructureRelational Data Models Basic Structure


17/33

17

Linking Relational Tables


18/33

18

ARelational Schema


19/33

19

SQL-based relational database application involves three parts:

User interface Allows end user to interact with data

Set of tables stored in database Each table is independent from another

Row

s in different tables related based on common valuesin common attributes

SQL engine Executes all queries

Relational Model (continued)


20/33

20

Advantages

Structural independence

Improved conceptual simplicity

Easier database design, implementation, management, and use

Ad hoc query capability (SQL)

Powerful database management system

Disadvantages

Substantial hardware and system software overhead

Possibility of poor design and implementation

Potential islands of information problems

Relational ModelRelational Model


21/33

21

Entity-Relationship Data Model

Introduced by Chen in 1976

One of the most widely accepted graphical data

modeling tools.

Graphically represents data as entities and theirrelationships in database structure.

Complements the relational data model concepts.


22/33

22

EntityRelationship Model - Basic Structure

Entity-Relationship model represented as entity/relationship(E/R)

diagram (see fig. 1.6, page 12)

An entity is represented by a rectangle:

- Entity is an object represented in a database (for example1.6,

Employees, rojects, Departments and so on are various objects)

- Each entity is described by a set ofproperties ( ropertiesdescribes particular characteristics of the entity)

- Relationship is represented by a diamond connected to the

related entities.


23/33

23

Entity and Relationships

Types of Relationships: One-to-many relationships (1:M)

A painter paints many different paintings, but each one ofthem is painted by only that painter.

PAINTER (1) paints PAINTING (M)

Many-to-many relationships (M:N)

An employee might learn many job skills, and each job skillmight be learned by many employees.

EMPLOYEE (M) learns SKILL (N)

One-to-one relationships (1:1)

Each store is managed by a single employee and each storemanager (employee) only manages a single store.

EMPLOYEE (1) manages STORE (1)


24/33

24

Relationship Depiction: The ERD


25/33

25

Relationship Depiction: The Crows Foot


26/33

26

Advantages

Exceptional conceptual simplicity

Visual representation

Effective communication tool

Integrated with relational database model

Disadvantages

Limited constraint representation

Limited relationship representation

No data manipulation language

E-R Data ModelsE-R Data Models


27/33

27

Object-Oriented (OO) Model

Semantic data model (SDM) developed by Hammer

and McLeod in 1981

Data and their relationships contained in a single

structure known as an object

Basis of object oriented data model (OODM)

OODM becomes the basis for the object oriented

database management system (OODBMS)


28/33

28

Object Oriented Data Model - Basic StructureOODM

Objects or abstractions of real-world entities arestored: Attributes describe properties

Collection of similar objects is a class

Methods represent real world actions of classes

Classes are organized in a class hierarchy

Inheritance is ability of object to inherit attributes and

methods of classes above it UML based on OO concepts that describe

diagrams and symbols Used to graphically model a system


29/33

29


30/33


31/33

31

The Development of Data Models


32/33

32

Data Models: Summary

Data Models and theirTasks:

Conceptual models (E-R Model): better suited for high-level data modeling

Implementation models (Network, & HierarchicalModels): better for managing stored data forimplementation purposes

Relational, & OODM: can be used as both conceptual &implementation models


33/33

33

Lecture 1b - Database Models

Documents