Download - Object oriented DB (not in book)

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Object oriented DB (not in book)

Database Systems: Design, Implementation, & Management, 6 th Edition, Rob & Coronel

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Learning objectives:

• What basic concepts govern OO systems

• How OO features are related to the more traditional relational and ER models

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

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


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Object Orientation and Its Benefits

• A set of design and development principles based on conceptually autonomous computer structures known as objects

• Each object represents a real-world entity with the ability to act upon itself and interact with other objects

• Modularity is therefore almost inevitable


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The Evolution of Object Oriented Concepts

• Object oriented programming

– Developed as an alternative to traditional programming methods

– Programmer creates or uses objects:

• Self-contained, reusable modules that contain data as well as the procedures used to operate on such data


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The Evolution of Object Oriented Concepts (continued)

• Object oriented programming languages were developed to:– Provide an easy-to-use software development

environment– Provide a powerful software modeling tool for

application development– Decrease development time by reducing the

amount of code– Improve programmer productivity by making

that code reusable


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The Evolution of Object Oriented Concepts (continued)

• Object oriented environment has several important attributes:

– Data set is no longer passive

– Data and procedures are bound together, creating an object

– Object has an innate ability to act on itself


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Object Oriented Concepts

• Have their roots in programming languages

• No knowledge of programming is necessary to understand these concepts


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Objects: Components and Characteristics

• Object:

– Abstract representation of a real-world entity

– Has:

• Unique identity

• Embedded properties

• Ability to interact with other objects and act upon itself

– Defining characteristic is its unique identity


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Real-World Student Objects


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Object Identity

• Unique to that object

• Assigned by system at moment of object’s creation

• Cannot be changed under any circumstances

• Can be deleted only if the object is deleted

• Can never be reused


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Attributes (Instance Variables)

• Attributes:

– Known as instance variables in OO environment

• Domain:

– Logically groups and describes the set of all possible values that an attribute can have


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Object Attributes


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Object State

• Set of values that object’s attributes have at a given time

• Can vary, although its OID remains the same

• To change the object’s state, change the values of the object’s attributes

• To change the object’s attribute values, send a message to the object

– Message will invoke a method


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Messages and Methods• Method:

– Code that performs a specific operation on object’s data

– Protects data from direct and unauthorized access by other objects

– Used to change the object’s attribute values or to return the value of selected object attributes

– Represent real-world actions


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Method Components


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Objects Send Messages to Each Other


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Classes

• Collection of similar objects with shared structure (attributes) and behavior (methods)

• Class instance or object instance

– Each object in a class


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Class Illustration


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Protocol

• An object’s public aspect

• How it is known by other objects as well as end users

• Other objects communicate with the student object using any of these methods


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Public and Private Aspects of an Object


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Musical Instruments Class Hierarchy


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Single Inheritance


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Multiple Inheritance


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Employee Class Hierarchy Method Override


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Employee Class Hierarchy Polymorphism


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Object Classification

• Simple object Only single value attributes

• Composite object Contains at least one multi-value attributes and no attributes that refer to other objects; ex: MOVIE

• Compound object : Contains attribute that refer to other objects. Ex: Advisor

• Associative object: represents relationship between two or more objects: ex: enrollment


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Characteristics of an Object Oriented Data Model

• Support the representation of complex objects

• Are extensible:– Capable of defining new data types as well as

the operations to be performed on them

• Support encapsulation:– Data representation and method’s

implementation must be hidden from external entities


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Characteristics of an Object Oriented Data Model (continued)

• Exhibit inheritance:

– Object must be able to inherit properties (data and methods) of other objects

• Support the notion of object identity (OID)


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Comparing the OO and ER Model Components


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Shared Representation for All Objects of the Class Person


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State of a Person Object Instance


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Referential Object Sharing


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Class Hierarchy


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Employee Object Representation


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Representing a 1:M Relationship


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Representing 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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Representing the M:N Relationship with Associated Attributes


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Representing the M:N Relationship with Intersection Class


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Object Space Representation


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Late and Early Binding: Use and Importance

• Late binding: – Data type of an attribute is not known until

execution time or runtime

– Two different object instances of the same class can contain values of different data types for the same attribute

• Early binding: – Allows database to check data type for each of

the attribute’s values at compilation or definition time


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INVENTORY Table with Predetermined (Base) Data Types


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Inventory Class with Early Binding


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OODM Inventory Class with Late Binding


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Support for Versioning

• Allows users to track history of changes in state of an object

• If the changes do not yield expected results, they can be undone and the component restored to its original state

• Reason OODBMS is such a strong player in the CAD and computer-aided manufacturing (CAM) arenas


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OODM and Previous Data Models: Similarities and Differences

• OODM object resembles entity and tuple in the ER and relational models but has additional characteristics

• Class • Hierarchies• Encapsulation • Object ID (OID) not supported• Relationships • OODM produces a schema in which relations

form part of the structure of the database


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An Invoice Representation


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Assume the following business rules:• A course contains many Sections, but each Section references only one

course.• A Section is taught by one professor, but each professor may teach one

or more different Sections of one or more courses.• A Section may contain many students, and each student may be enrolled

in many Sections.• A Section may contain many students, and each student is enrolled in

many Sections, but each Section belongs to a different course. (Students may take many courses, but they cannot take many Sections of the same course!)

• Each Section is taught in one room, but each room may be used to teach different Sections of one or more courses.

• A professor advises many students, but a student has only one advisor.Based on these business rules:• a. Identify and describe the main classes of objects.• B. Draw the object oriented diagram


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• See figure p3.8 on 7/p95 • Draw object oriented diagram for it


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Object Oriented Database Management Systems

• Integrate benefits of typical database systems with the more powerful modeling and computational (programming) characteristics of the object oriented data model

• Used to develop complex systems


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• Result of combining OO features, such as– class inheritance– encapsulation, and

– polymorphism, • With database features such as

– data integrity, -- data manipulation,– security, -- system tuning and– persistence, -- recovery– transaction management, – concurrency control, – backup,


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How Object Orientation Affects Database Design

• Relational and ER models sometimes cannot adequately represent some objects

• Operations are not a part of the database model

• Object oriented design requires the database description to include objects and their data representation, constraints, and operations

• Few computerized OODB design tools exist• Lack of standards affects object oriented

database design


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OODBMS:Advantages and Disadvantages

• OODBMS occupies a strong niche market

• Vehicle for technological innovation

• Has not been the beneficiary of market share growth

Download - Object oriented DB (not in book)

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