Database Models

1
Database Models
2
Learning Objectives

• What database models exist
• Hierarchical database model
• Network database model
• Relational database model
• Entity-Relationship database model
• Object-oriented database model
• What is the evolution of database models

3
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 access language and application
  programming interfaces Data Definition
  Language (DDL) and Data Manipulation Language
  (DML)
• Database communication interfaces

4
Database Modeling

• A model is an abstraction of the real world, or
  of part of the real world.
• To develop database systems, we will
• First build a model of the application domain
• Then build a design for the application
• Then implement the design
• Spending time on the modeling and design aspects
  of the process saves time later on.

5
Database Models

• Collection of logical constructs used to
  represent data structure and relationships within
  the database
• Conceptual models logical nature of data
  representation
• Implementation models emphasis on how the data
  are represented in the database

6
Database Models

• Types of database models
• Conceptual database models represent the
  entities objects and relationships in the
  application domain
• E-R
• Object Oriented (UML)
• Semantic
• Implementation database models represent the
  software application entities objects and
  relationships
• Hierarchical
• Network
• Relational

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Database Models (cont.)

• Relationships in Conceptual Models
• One-to-one (11) Ex Manager/Store
• One-to-many (1M) Ex Agent/Customer
• Many-to-many (MN) Ex Course/Student
• Implementation Database Models
• Hierarchical
• Network
• Relational

8
The DBMS Marketplace

• Relational DBMS companies Oracle, Sybase are
  among the largest software companies in the
  world.
• IBM offers its relational DB2 system. With IMS,
  a nonrelational system, IBM is by some accounts
  the largest DBMS vendor in the world.
• Microsoft offers SQL-Server, plus Microsoft
  Access for the cheap DBMS on the desktop,
  answered by lite systems from other
  competitors.
• Relational companies also challenged by
  object-oriented DB companies.
• But countered with object-relational systems,
  which retain the relational core while allowing
  type extension as in OO systems.

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Hierarchical Database Model

• History
• North American Rockwell developed GUAM
  (Generalized Update Access Method)
• Mid 1960s Rockwell partner with IBM to create
  Information Management System (IMS)
• IMS DB/DC lead the mainframe database market in
  70s and early 80s
• Represents well hoe components are decomposed
  into parts

10
Hierarchical Database Model

• Logically represented by an upside down tree
• Each parent can have many children
• Each child has only one parent

Figure 1.8
11
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 use complexity
• Implementation limitations (no MN relationship)

12
Network Database Model

• History
• CODASYL (Conference on Data Systems Languages)
  created a group to work on standardization of
  databases Database Task Group (DBTG)
• Identified 3 database component
• Network schema (database organization)
• Subschema (views of database per user)
• Data management language

13
Network Database Model

• Each record can have multiple parents
• Composed of sets - relationships
• Each set has owner record and member record
• Member may have several owners
• A set represents a 1M relationship between the
  owner and the member

Figure 1.10
14
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

15
Relational Database Model

• First developed by E.F. Codd (IBM) in 1970
• First deployed on mainframe computers (DB2), then
  also personal computers
• Oracle, Informix, SQL server, DB2

16
Relational Database Model

• Perceived by user as a collection of tables for
  data storage
• Tables are a series of row/column intersections
  (a row corresponds to a record, a column to a
  field)
• Tables related by sharing common entity
  characteristic(s)
• RDBMS

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Relational Database Model (cont.)
Figure 1.11
18
Relational Database Model

• Advantages
• Structural independence
• Improved conceptual simplicity
• Easier database design, implementation,
  management, and use
• Ad hoc query capability with SQL
• Powerful database management system

19
Relational Database Model

• Disadvantages
• Substantial hardware and system software overhead
• Poor design and implementation is made easy
• May promote islands of information problems

20
Entity Relationship Database Model

• Complements the relational data model concepts
• Represented in an entity relationship diagram
  (ERD)
• Based on entities, attributes, and relationships

Figure 1.13
21
Entity Relationship Database Model

• Chens model
• Crows Foot model

22
Entity/Relationship Model

• Diagrams to represent conceptual models and
  designs
• Entity like object, thing.
• Entity set like class set of similar
  entities/objects.
• Attribute property of entities in an entity
  set, similar to fields of a struct.
• In diagrams, entity set ? rectangleattribute ?
  oval.

name
phone
ID
Students
height
23
Relationships

• Connect two or more entity sets.
• Represented by diamonds.

Taking
Students
Courses
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Summary of Symbols Used in E-R Notation
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Summary of Symbols (Cont.)
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Alternative E-R Notations
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Relationship Set

• Think of the value of a relationship set as a
  table.
• One column for each of the connected entity sets.
• One row for each list of entities, one from each
  set, that are connected by the relationship.
• Students Courses
• Sally CS180
• Sally CS111
• Joe CS180

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Multiway Relationships

• Usually binary relationships (connecting two
  E.S.) suffice.
• However, there are some cases where three or more
  E.S. must be connected by one relationship.
• Example relationship among students, courses,
  TA's (and graders).
• Possibly, this E/R diagram is OK

Taking
Students
Courses
Assisting
TA/Graders
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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 of classes
• Classes are organized in a class hierarchy
• Inheritance is ability of object to inherit
  attributes and methods of classes above it

31
OO Data Model

• Advantages
• Adds semantic content
• Visual presentation includes semantic content
• Database integrity
• Both structural and data independence
• Disadvantages
• Lack of OODM
• Complex navigational data access
• Steep learning curve
• High system overhead slows transactions

32
Database Models and the Internet

• Characteristics of Internet age databases
• Flexible, efficient, and secure Internet access
• Easily used, developed, and supported
• Supports complex data types and relationships
• Seamless interfaces with multiple data sources
  and structures
• Simplicity of conceptual database model
• Many database design, implementation, and
  application development tools
• Powerful DBMS GUI make DBA job easier

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60s 70's 80's 90s now
Hierarchical
Network
Relational
Choice for most new applications
Object Bases
Knowledge Bases