Database Systems: Design, Implementation & Management

Chapter 11

Object-Oriented Databases

Database Systems: Design, Implementation, and

Management, Fifth Edition, Rob and Coronel

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In this chapter, you will learn:

• What basic concepts govern OO systems

• What effect OO concepts are likely to have on data modeling and design

• How OO features are related to the more traditional relational and E-R models

• What the basic features of an OO database management system (OODBMS) are

• About the advantages and disadvantages of

OODBMSs

Database Systems: Design, Implementation, & Management, 5 th Edition, Rob & Coronel

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Object Orientation

• Object Orientation

– Set of design and development principles

–

Based on autonomous computer structures known as objects

• OO Contribution areas

– Programming Languages

– Graphical User Interfaces

– Databases

– Design

–

Operating Systems


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Evolution of OO Concepts

• Concepts stem from object-oriented programming languages (OOPLs)

– Ada, ALGOL, LISP, SIMULA

• OOPLs goals

– Easy-to-use development environment

– Powerful modeling tools for development

– Decrease in development time

– Make reusable code

• OO Attributes

– Data set not passive

– Data and procedures bound together

– Objects can act on self


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OO Concepts: Objects

• Abstract representation of a real-world entity

– Unique identity

–

Embedded properties

– Ability to interact with other objects and self

• OID

– Unique to object

– Not a primary key

• Attributes

– Called instance variables

– Domain

• Object state

– Object values at any given time


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OO Concepts: Objects (con’t.)

• Methods

– Code that performs operation on object’s data

–

Has name and body

• Messages

– Invokes method

– Sent to object

• Classes

– Collection of similar objects

– Shares attributes and structure

• Protocol

– Represents object’s public aspect


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OO Concepts: Objects (con’t.)

• Class hierarchy

– Code that performs operation on object’s data

– Has name and body

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Object Characteristics

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Figure 11.7

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Class Hierarchy

• Superclass

• Subclass

• Class lattice

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Figure 11.8

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Inheritance

• Ability of object to inherit the data structure and behavior of classes above it

• Single inheritance

– Class has one immediate superclass

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Figure 11.9


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Inheritance (con’t.)

• Multiple

– Class has more than one immediate superclass

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Figure 11.10


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Method Overriding

• Method redefined at subclass level

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Figure 11.12

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Polymorphism

Allows different objects to respond to same message in different ways

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Figure 11.13

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Abstract Data Types (ADT)

• Describes a set of similar objects

• Differs from conventional data types

– Operations are user-defined

– Uses encapsulation

•

Definitions needed for creation

– Name

– Data representation

– Abstract data type operations and constraints


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Object Classification

• Simple

– Only single-valued attributes

–

No attributes refer to other object

• Composite

– At least one multivalued attribute

– No attributes refer to other object

• Compound

– At least one attribute that references other object

• Hybrid

– Repeating group of attributes

– At least one refers to other object


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Characteristics of OODM

• Supports complex objects

• Must be extensible

• Supports encapsulation

• Exhibit inheritance

• Supports object identity


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OO vs. E-R Model Components

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Table 11.3

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Shared Representation for all Objects of the Class Person

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Figure 11.14


Figure 11.15

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Referential Sharing of Objects

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Figure 11.19


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Class-Subclass Relationship

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Figure 11.20


Figure 11.21

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Interobject Relationships

• Attribute-Class Link

• Object’s attribute references another object

• Relationship Representation

–

Related classes enclosed in boxes

– Double line on right side indicates mandatory

–

Connectivity indicated by labeling each box

• 1:M

• M:N

• M:N with an Intersection Class


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1:1 and 1:M Relationships

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Figure 11.24

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Employee-Dependent Relationship

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Figure 11.25

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Representing the M:N Relationship

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Figure 11.26

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Representing the M:N Relationship with Associated Attributes

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Figure 11.27

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Representing the M:N Relationship with Intersection Class

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Figure 11.28

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Object Space Representation

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Figure 11.29


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Late and Early Binding

• Late binding

– Data type of attribute not known until runtime

– Allows different instances of same class to contain different data types for same attribute

• Early binding

– Allows database to check data type at compilation or definition time

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OODM vs. E-R Data Models

• Object, Entity, and Tuple

– OODM object has behavior, inheritance, and encapsulation

– OO modeling more natural

• Class, Entity Set, and Table

– Class allows description of data and behavior

– Class allows abstract data types

• Encapsulation and Inheritance

– Object inherits properties of superclasses

– Encapsulation hides data representation and method


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OODM vs. ER Data Models (con’t.)

• Object ID

– Not supported in relational models

• Relationships

– OODM

• Interclass references

• Class hierarchy inheritance

– Relational models

• Value-based approach

• Access

– Relational models

• SQL

– OODM

• Navigational

• Set-oriented access


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OODBMS

• Database management system integrates benefits of typical database systems with OODM characteristics

• Handles a mix of data types

• Follows OO rules

• Follows DBMS rules

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OO and Database Design

• Provides data identification and the procedures for data manipulation

• Data and procedures self-contained entity

• Iterative and incremental

• DBA does more programming

• Lack of standards

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OODBMS Advantages

• More semantic information

• Support for complex objects

• Extensibility of data types

• May improve performance with efficient caching

• Versioning

• Reusability

• Inheritance speeds development and application

• Potential to integrate DBMSs into single environment


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OODBMS Disadvantages

• Strong opposition from the established

RDBMSs

• Lack of theoretical foundation

• Throwback to old pointer systems

• Lack of standard ad hoc query language

• Lack of business data design and management tools

• Steep learning curve

• Low market presence

• Lack of compatibility between different

OODBMSs


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OO Influences on Relational Model

• Extensibility of new user-defined (abstract) data types

• Complex objects

• Inheritance

• Procedure calls (rules or triggers)

• System-generated identifiers (OID surrogates)


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The Next Generation of DBMS

• Object-oriented database systems

• Artificial intelligence systems

• Expert systems

• Distributed database

• The Internet


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Database Systems: Design, Implementation & Management

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