Use Case Modeling-Object-Oriented Design-Lecture 5 Slides-Computer Engineering, Slides of Object Oriented Analysis and Design

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1 Sharif University of Technology

Object-Oriented Design Lecturer: Raman Ramsin

Lecture 5: Use Case Modeling

Part 2

2 Object-Oriented Design – Lecture 5

Activities of requirements workflow Capture Functional Requirements^ 1.

Find actors and use cases

Prioritize use cases

3.

Detail use cases

Prototype user interface

5. Structure the use-case model

4 Object-Oriented Design – Lecture 5

Actor Generalization^ „

If two actors communicate with the same set of usecases in the same way, we can express this as ageneralization to another (possibly abstract) actor.

5 Object-Oriented Design – Lecture 5

Use Case Generalization^ „

Used when one or more use cases are really specializations ofa more general case. „ Child use cases may:

inherit features from their parent use case

add new features

override (change) inherited features (except for inheritedrelationships and extension points) „ Use case generalization is documented in use casespecifications using a simple tag language on flow steps.There are two rules:

Each step number in the child is postfixed by the equivalentstep number in the parent if there is one.

If the step in the child overrides a parent step, it ispostfixed by "o" (for overridden) and then the step numberin the parent.

7 Object-Oriented Design – Lecture 5

«include» Relationship^ „

The «include» relationship between use cases allowsyou to include the behavior of one use case into the flowof another use case.

8 Object-Oriented Design – Lecture 5 Sharif University of Technology

«include» Relationship: Specification^ „

The base use case is not complete without all of its inclusion use cases. „ Inclusion use cases may be complete ( instantiable) or incomplete ( behavior fragments)

10 Object-Oriented Design – Lecture 5

«extend» Relationship: Example

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«extend» Relationship: Extension Points

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Extension Use Case: Single-Segment Example

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Extension Use Case: Multiple-Segment Example

16 Object-Oriented Design – Lecture 5 Sharif University of Technology

«extend» Relationship: Rules^ „

The «extend» relationship must specify one or more ofthe extension points in the base use case or it isassumed that the «extend» relationship refers to

all

extension points. „ The extension use case must have the same number ofinsertion segments as there are extension pointsspecified in the «extend» relationship. „ It is legal for two extension use cases to «extend» thesame base use case at the same extension point. But ifthis happens, the order in which the extensions executeis indeterminate.

17 Object-Oriented Design – Lecture 5

Use Case Modeling: Hints and Tips - 1^ 1.

Keep use cases short and simple

Include only enough detail to capture therequirements.

A good rule of thumb is to ensure that the mainflow of a use case fits on a single side of paper. „ Start by simplifying the text „ Remove any design details „ Reanalyze the problem: Are there more thanone use case? Can alternative flows befactored out?

19 Object-Oriented Design – Lecture 5

Use Case Modeling: Hints and Tips - 3^ 3.

Avoid functional decomposition

• Functional Decomposition in Use Case Modeling: creating a set of "high level" use cases, and thenbreaking these down into a set of lower-level usecases and so on, until "primitive" use cases arereached that are detailed enough to beimplemented.

20 Object-Oriented Design – Lecture 5 Functional Decomposition in Use Case Modeling: Example