Ch 5 O O Data Modeling

Modern Database Management Jeffrey A. Hoffer, Mary B. Prescott, Fred R. McFadden Object-Oriented Data Modeling

What is Object Oriented Data 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

Figure 14-1 – Phases of object-oriented systems development cycle

OO vs. EER Data Modeling Object Oriented EER Class Entity type Object Entity instance Association Relationship Inheritance of attributes Inheritance of attributes Inheritance of behavior No representation of behavior Object-oriented modeling is frequently accomplished using the Unified Modeling Language (UML)

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 Artifact of the Design Process: user interface, controller, scheduler Objects exhibit BEHAVIOR as well as attributes  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, even if all of its attribute values are the same

Figure 14-2 – UML class and object diagrams (a) Class diagram showing two classes Class diagram shows the static structure of an object-oriented model: object classes, internal structure, relationships. Behavior

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

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

Figure 14-3 – 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

Figure 14-4 – Examples of binary association relationships (a) University example Alternative multiplicity representation: specifying the two possible values in a list instead of a range

Figure 14-5 – Object diagram for customer order example

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

Figure 14-6 – Association class and link object (a) Class diagram showing association classes Binary association class with behavior Unary association with only attributes and no behavior

(b) Object diagram showing link objects Association class instances

Figure 14-7 –Ternary relationship with association class

Figure 14-8 – Derived attribute, association, and role Derived attributes an 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

Figure 14-9 – Examples of generalization, inheritance, and constraints (a) Employee superclass with three subclasses Shared attributes and operations An employee can only be one of these subclasses An employee may be none of them. Specialized attributes and operations

(a) Abstract patient class with two concrete subclasses Abstract indicated by italics Dynamic means a patient can change from one subclass to another over time A patient MUST be EXACTLY one of the subtypes

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.

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

Figure 14-11 – Polymorphism, abstract operation, class-scope attribute, and ordering Class-level attributes – only one value common to all instances of these clases This operation is abstract…it has no method at Student level Methods are defined at subclass level

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.

Figure 14-12 – Overriding inheritance Restrict job placement

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.

Figure 14-13 Multiple inheritance

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.

Figure 14-14 – Example aggregation

Figure 14-15 – Aggregation and Composition (a) Class diagram (b) Object diagram

Figure 14-16 – Recursive aggregation

Business Rules See chapters 3 and 4 Implicit and explicit constraints on objects – for example: cardinality constraints on association roles ordering constraints on association roles Business rules involving two graphical symbols: labeled dashed arrow from one to the other Business rules involving three or more graphical symbols: note with dashed lines to each symbol

Figure 14-17 – Representing business rules Three-symbol constraint Two-symbol constraint

Figure 14-18 – Class diagram for Pine Valley Furniture Company

Ch 5 O O Data Modeling

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Ch 5 O O Data Modeling