Object-Oriented Databases

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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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• 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

Evolution of OO Concepts

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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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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

Table 11.3

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Referential Sharing of Objects

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Class-Subclass Relationship

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• 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

Interobject Relationships

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1:1 and 1:M Relationships

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Employee-Dependent Relationship

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Representing the M:N Relationship

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• 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

Late and Early Binding

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• 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

OODM vs. E-R Data Models

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• Object ID– Not supported in

relational models

• Relationships– OODM

• Interclass references

• Class hierarchy inheritance

– Relational models

• Value-based approach

OODM vs. E-R Data Models (con’t.)

• 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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• 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

OO and Database Design

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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