Object Modeling

J. Stephen SchiavoMissouri Southern State University

Object Modeling

DefinitionConcepts

Objects, attributes, methods, encapsulationClasses, generalization, specializationObject/class relationshipMessagesPolymorphism

Modeling process

Definition

Object-Oriented Analysis & Design:The application of objects to understanding existing systems, and in specifying new or improved systemsObject Modeling:Technique for identifying objects in the system and the relationships among them

Concepts

Objects: Entities in the environment, capable of being seen, touched, sensed; and of experiencing events.Attributes: characteristics of objectsBehavior(s): Things an object can do, or you can do to an object: methodsEncapsulation: packaging attributes and methods together in the object.

Concepts …

Classes: set of objects with common attributes and behaviors.

Retail Stores, Students, Vehicles, …

Generalization: gathering common aspects of similar classes to form a super-type

Specialization: distinguishing one instance of a class by adding or modifying attributes or methods to create a subtype.

Classes / Sub & Super Classes

Students:Maj, Advr, Hrs

Faculty:Ten, TrmDeg

Admin’r:Level, Vac

Employee:Dep, Sal, Ins

SSN, Name, Addr, Phone;

Concepts …

Object/class relationships:Natural relationship among classes, just as in the entity-relationship data modelMessages: How one object interacts with, i.e, how it calls or uses another objectPolymorphism: Behaviors of the same name can differ markedly with objects.“Shut” is a different action for objects door, window, suitcase, drawer, faucet, mouth.

Modeling processIdentifying objects

Use case (‘yooss’ case)modeling – scenarios

Use case: sequence of steps in a task

Actor: anything interacting with system;a user or role; internal, or external

Organizing objects and relationshipsObject Association Model

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Identifying objects1. Identify actors (people, places, & things)

and use cases (transactions)2. Constructing the use case model diagram:

Which actors involved in which cases3. Documenting use case course of events

a. Name the initiating actorb. Generally describe the transactionc. Step-by-step process through typical cased. Pre-and-post conditions (before and after case)e. Assumptions: performance, security, etc.

Figure 8.9

Identifying objects …

4. Identifying use case dependencies showing which case must follow which

5. Document alternative course of events for non-typical situations: an order from a credit-impaired client; booking a flight for a disabled person or for a VIP ( or for a disabled VIP!) …

6. Finding potential objects, selecting objects: remove duplicates (synonyms), actors outside the system, non-unique actors, etc…

Organizing objects and relationships1. Identify associations and multiplicity:

what one object needs to know about or do to (or do with) another object

2. Identifying generalizations and specializations … subtypes/super-types … as in person employee manager

3. Identifying aggregation relationships(is part of …), e.g., Truck cab & trailer

4. Preparing the object association model(Figure 8.16) What does this remind you of?