Database Management System

Prepared by Dr. Ahmed El-Ragal

Reviewed & Presented By Mr. Mahmoud Rafeek Alfarra

College Of Science & Technology Khan younisInformation Technology & Computer Science Dep.

Part 9Object-Oriented Database Modeling

What is Object Oriented Database Modeling?

Centers around objects and classes. Involves inheritance.Encapsulates both data and behavior.Benefits of Object-Oriented Modeling:

Ability to tackle challenging problems.Improved communication between users, analysts, designer,

and programmers.Increased consistency in analysis and design.Explicit representation of commonality among system

components.System robustness.Reusability of analysis, design, and programming results.

2

Overview

Object-oriented techniques work well in situations where complicated systems are undergoing continuous maintenance, adaptation, and design.

There are two ways to model object-oriented systems:Coad and Yourdon methodology.The Unified Modeling Language.

3

6 ideas

Six ideas characterize object-oriented modeling:

An object, which represents a real-world thing or event.A class, or group of related objects.Messages, sent between objects.Encapsulation, only an object makes changes through its

own behavior.Inheritance, a new class created from another class.Polymorphism, meaning that a derived class behavior

may be different from the base class.

4

Naming

Another name for property is attribute.Another name for method is operation.

5

OO vs. EER Data Modeling

Object Oriented

6

EER

Object Class Entity typeObject Instance Entity instanceAssociation RelationshipInheritance of attributes Inheritance of attributesInheritance of behavior No representation of behavior

Object

An entity that has a well-defined role in the application domain, as well as state, behavior, and identity.

Tangible: person, place or thing.Concept or Event: department, performance,

marriage, registration.

7

ObjectsObjects exhibit BEHAVIOR as well as attributes Different from entitiesentities

State, Behavior, Identity

State: attribute types and values.

Behavior: how an object acts and reacts.Behavior is expressed through operations that can

be performed on it.

Identity: every object has a unique identity.

8

9

10

11

Five-Layer Model

Object oriented analysis and design is based on a five-layer model:Class/object layer notes the classes and objects.Structure layer captures various structures of classes

and objects, such as one-to-many relationships and inheritance.

Attribute layer details the attributes of classes.Service layer notes messages and object behaviors.Subject layer divides the design into implementation

units or team assignments.

12

13

14

15

UML class and object diagrams

(a) Class diagram showing two classes

Class diagramClass diagram shows the static structure of an object-oriented model: object classes, internal structure, relationships.

16

(b) Object diagram with two instances

Object diagramObject diagram shows instances that are compatible with a given class diagram.

Operations

A function or service that is provided by all instances of a class.

Types of operators:ConstructorConstructor: creates a new instance of a class.QueryQuery: accesses the state of an object but does not alter its

state.UpdateUpdate: alters the state of an object.ScopeScope: operation applying to the class instead of an

instance.

17

Operations implement the object’s behaviorbehavior

18

Encapsulation

An object is an encapsulated structure, having both attributes and methods.

The term encapsulation means that it is complete in itself. Programs external to an object know nothing of its structure and

need to know nothing of that. The external appearance of an object is referred to as interface. The interface consists of attributes and methods that are visible to

the outside world. The encapsulated internal structure of an object is referred to as

implementation. An OO object may have a method to create itself, display itself,

and modify itself. Any of these methods is a program. OO objects interact by calling each other’s methods. Since all

objects are encapsulated none need to know others’ structure.

19

20

Associations

AssociationAssociation: Relationship among object classes

Association RoleAssociation Role: Role of an object in an association The end of an association where it connects to a class

MultiplicityMultiplicity: How many objects participate in an association.

Lower-bound..Upper bound (cardinality).

21

22

23

Association relationships of different degrees

Lower-bound – upper-bound

Represented as: 0..1, 0..*, 1..1, 1..*

Similar to minimum/maximum cardinality rules in EER

24

Examples of binary association relationships (a) University example

Alternative multiplicity representation: specifying the two possible values in a list

instead of a range

Association ClassAn association that has attributes or

operations of its own or that participates in relationships with other classes.

Like an associative entity in ER model.$

25

26

Association class and link object

(a) Class diagram showing association classes

Binary association class with behavior

Unary association with only attributes and no behavior

27

(b) Object diagram showing link objects

Association class instances

28

Derived attribute, association, and role

Derived attributes and relationships shown with / / in front of the name

Derived relationship (from Registers-for and Scheduled-for)

Constraint expression for derived attribute

Derived attribute

Generalization/SpecializationSubclass, superclass

similar to subtype/supertype in EERCommon attributes, relationships, AND

operationsDisjoint vs. OverlappingComplete (total specialization) vs.

incomplete (partial specialization)Abstract Class: no direct instances???Concrete Class: direct instances???

29

Class-Level AttributeSpecifies a value common to an entire

class, rather than a specific value for an instance.

Represented by underlining

“=“ is initial, default value.

30

PolymorphismAbstract Operation: Defines the form or

protocol of the operation, but not its implementation.

Method: The implementation of an operation.

Polymorphism: The same operation may apply to two or more classes in different ways.

31

32

Overriding Inheritance

Overriding: The process of replacing a method inherited from a superclass by a more specific implementation of that method in a subclass..For Extension: add code.For Restriction: limit the method. For Optimization: improve code by exploiting

restrictions imposed by the subclass.

33

Multiple InheritanceMultiple Classification: An object is an

instance of more than one class.

Multiple Inheritance: A class inherits features from more than one superclass.

34

35

Multiple inheritance

AggregationAggregation: A part-of relationship between a

component object and an aggregate object.

Composition: A stronger form of aggregation in which a part object belongs to only one whole object and exists only as part of the whole object.

Recursive Aggregation: composition where component object is an instance of the same class as the aggregate object.

36

37

Example aggregation

38

Aggregation and Composition

(a) Class diagram

(b) Object diagram

39

Recursive aggregation

Reviewed By Mr. Mahmoud Rafeek Alfarra