Database Management System Prepared by Dr. Ahmed El-Ragal Reviewed & Presented By Mr. Mahmoud Rafeek Alfarra College Of Science & Technology Khan younis Information Technology & Computer Science Dep. Part 9 Object-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 ClassEntity type Object InstanceEntity instance AssociationRelationship Inheritance of attributes Inheritance 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 Objects Objects exhibit BEHAVIOR as well as attributes entities  Different from entities

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

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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

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15 UML class and object diagrams (a) Class diagram showing two classes Class diagram Class diagram shows the static structure of an object-oriented model: object classes, internal structure, relationships.

16 (b) Object diagram with two instances Object diagram Object 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: Constructor Constructor: creates a new instance of a class. Query Query: accesses the state of an object but does not alter its state. Update Update: alters the state of an object. Scope Scope: operation applying to the class instead of an instance. 17 behavior Operations implement the object’s behavior

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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

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Associations Association Association: Relationship among object classes Association Role Association Role: Role of an object in an association The end of an association where it connects to a class Multiplicity Multiplicity: How many objects participate in an association. Lower-bound..Upper bound (cardinality). 21

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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 Class An 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/Specialization Subclass, superclass similar to subtype/supertype in EER Common attributes, relationships, AND operations Disjoint vs. Overlapping Complete (total specialization) vs. incomplete (partial specialization) Abstract Class: no direct instances??? Concrete Class: direct instances??? 29

Class-Level Attribute Specifies a value common to an entire class, rather than a specific value for an instance. Represented by underlining “=“ is initial, default value. 30

Polymorphism Abstract 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

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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 Inheritance Multiple Classification: An object is an instance of more than one class. Multiple Inheritance: A class inherits features from more than one superclass. 34

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Aggregation Aggregation: 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