1. Chapter 7: The Object-Oriented Approach to Requirements
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2. Learning Objectives Develop use case diagrams
Write use case and scenario descriptions
Develop activity diagrams and system sequence diagrams
Refine and enhance the domain model class diagram
Explain how UML diagrams work together to define functional requirements for the object-oriented approach
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3. Overview
Objective of requirements definition is understanding user’s needs, business processes, and system to support business processes
Understand and define requirements for a new system using object-oriented analysis models and techniques
Line between object-oriented analysis and object-oriented design is somewhat fuzzy
Iterative approach to development
Models built in analysis are refined during design
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4. The Unified Modeling Language and the Object Management Group
Object-oriented modeling notation is Unified Modeling Language (UML)
UML was presented to Object Management Group (OMG) as standard modeling technique
Purpose of Object Management Group
Promote theory and practice of object technology for development of distributed systems
Provide common architectural framework for OO
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5. Object-Oriented Requirements
Systems development process starts with identification of events and things
Events are business processes that new system must address
Things are problem domain objects involved in business process
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6. Object-Oriented Approach Models
Class diagram – definition of system components
Use case diagrams and use case descriptions – show user roles and how they use the system
Systems sequence diagrams (SSDs) – define inputs and outputs and sequence of interactions between user and system for a use case
Statechart diagrams – describe states of each object
Activity diagrams – describe user activities
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7. Requirements Diagrams: Traditional and OO Models
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8. The System Activities – A Use Case / Scenario View
Use case analysis used to identify and define all business processes that system must support
Use Case - single function performed by system for those who use that function
Actors
Role played by user
Outside automation boundary and organization
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9. Use Case Diagram
Graphical models that summarize information about actors and use cases
System developer
Looks at system as whole
Identifies major uses from event table
Identifies functions to be supported by new system
Organizes use cases
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10. Simple Use Case with an Actor
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11. Use Case Diagram with System Boundary
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12. Use Case of Customer Support System
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13. All Use Cases Including Customer
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14. <<Includes>> Relationships
Documents situation where one use case requires the services of a common subroutine
Another use case is developed for this common subroutine
A common use case can be reused by multiple use cases
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15. <<includes>>
Example of Order-Entry Subsystem with <<Includes>> Use Cases (Figure 7-6)
<<includes>>
Common
Subroutines
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16. Developing a Use Case Diagram
Starting points for use case development
Use event table
Identify all actors of the system
Identify functions actors perform with system
Develop flow of activities to identify various scenarios
Common internal use cases can be identified and separated into different use cases
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17. CRUD analysis CRUD – Create, Read/Report, Update, Delete
Information Engineering (IE) technique to identify event table events or develop use case diagram
Compares identified use cases with domain model class diagram
Every class in class diagram must have use cases to support creating, reading, reporting, updating, and deleting object instances
Confirms system integration requirements
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18. Use Case Detailed Descriptions
Scenario, or use case instance, details sequence of activities within use case
Shows actor interacting with computer system step-by-step to carry out business activity
May have several scenarios for single use case
Analysts prefer to write narrative descriptions of use cases instead of building activity diagrams
Three levels: brief, intermediate, and fully developed description
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19. Brief Description of Create New Order Use Case
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20. Intermediate Description of the Telephone Order Scenario for Create New Order
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21. Intermediate Description of the Web Order Scenario for Create New Order
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22. Fully Developed Description of Telephone Order Scenario for Create New Order
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23. Fully Developed Description of Web Order Scenario for Create New Order
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24. Activity Diagrams
Used to document work flow of business process activities for each use case scenario
Standard UML diagram
Can support any level of use case description
Helpful in developing system sequence diagrams
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25. Activity Diagram: Telephone Order Scenario
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26. Activity Diagram: Web Order Scenario
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27. Identifying Inputs and Outputs – The System Sequence Diagram
Collaboration diagram
Emphasizes objects that interact together to support a use case diagram
May be used alone or with sequence diagram
System sequence diagram
Shows sequence of interactions between objects and flow of events in a single use case
Focuses on message details
Used more frequently in industry
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28. Sample System Sequence Diagram (SSD)
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29. SSD Notation
Actor represented by stick figure – person (or role) that “interacts” with system by entering input data and receiving output data
Object notation is rectangle with name of object underlined – shows individual object and not class of all similar objects
Lifeline is vertical line under object or actor to show passage of time for object
Messages use arrows to show messages sent or received by actor or system
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30. SSD Lifelines Vertical line under object or actor:
Shows passage of time
If vertical line dashed:
Creation and destruction of thing is not important for scenario
Long narrow rectangles:
Activation lifelines emphasize that object is active only during part of scenario
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31. SSD Messages
Internal events identified by the flow of objects within a scenario
Requests from one actor or object to another to do some action
Invokes a particular method
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32. Repeating Message
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33. Developing a System Sequence Diagram
Begin with detailed description of use case from fully developed form or activity diagrams
Identify input messages
Describe message from external actor to system using message notation
Identify and add any special conditions on input message, including iteration and true/false conditions
Identify and add output return messages
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34. Simplified Activity Diagram of the Telephone Order Scenario
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35. SSD of Simplified Telephone Order Scenario for Create New Order Use Case
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36. SSD of the Web Order Scenario for the Create New Order Use Case
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37. Problem Domain Modeling – The Domain Model Class Diagram
Class diagram is focal point of object-oriented development
Provides definition of system components
Contains important class structural information for implementation with object-oriented programming
Provides conceptual data model to describe classes for database definition
Consists of problem domain classes and implementation classes
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38. Example of Domain Model Class Diagram
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39. RMO Domain Model Class Diagram
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40. Integrating Object-Oriented Models
Complete use case diagram is needed to understand total scope of new system
Domain model class diagrams also should be as complete as possible for entire system
With iterative approach, only construct use case descriptions, activity diagrams, and system sequence diagrams for use cases in iteration
Development of a new diagram often helps refine and correct previous diagrams
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41. Relationships Between OO Requirements Models
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42. Use Case Diagram for Inventory System
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43. Relationships Between OO Requirements Models (Figure 7-28)
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44. Summary
Object-oriented approach has complete set of diagrams that together document the user’s need and define system requirements
Requirements specified using following models:
Domain model class diagrams
Use case diagrams
Use case detailed model, either descriptive format or activity diagram
System sequence diagrams (SSDs)
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