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Ooa 2 Post1

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Object-oriented analysis and design(OOAD) UML Slides. for more slides refer www.scmGalaxy.com.

Object-oriented analysis and design(OOAD) UML Slides. for more slides refer www.scmGalaxy.com.

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Transcript

  • 1. SYSTEM BEHAVIOR SYSTEM SEQUENCE DIAGRAMS Objectives
    • Identify system events and system operations
    • Create system sequence diagrams for use cases
    • Create system class
    • Write contract to each system operations
  • 2. System Behavior:
    • Before proceeding to a logical design of how a software application will work, it is necessary to investigate and define its behavior as a “black box.”
    • System behavior is a description of “what a system does”, without explaining how it does .
    System as Black Box
  • 3. System sequence diagram for POST System
  • 4. Recording System Operations:
    • The set of all required system operations is determined by identifying the system events with parameters.
    • Where should these operations be recorded?
    • The UML includes notation to
    • record operations of a type, as
    • shown in Figure
    TypeX Operation1() operation2() Operations of the type POST enterItem(upc,quantity) endSale() makePayment(amount) Operations of the type
  • 5. Operation Contracts Post condition Pre- condition Responsibility Notes Exceptions Out Put
  • 6. SYSTEM BEHAVIOR CONTRACTS
    • It is missing details necessary to understand the system response [i.e. system behavior]
    • In general, a contract is a document that describes what an operation commits to achieve.
    • It is usually “ declarative in style” , emphasizing “what will happen ”, rather than how it will be achieved.
  • 7. Responsibility Section
    • Under this section , an informal description of the responsibilities this operation must fulfill, should be written.
      • ( Responsibility of Operation is ” Functionality of an Operation in a specific context ”)
    Notes Section
    • The Notes section of the contract is a place where design statements may be made regarding the operation.
    • For example:
        • documenting a particular algorithm is preferred to handle this operation
        • Pseudocode for this algorithm
  • 8. Pre-conditions
    • The pre-conditions define assumptions about the state of the system at the beginning of the operation.
    Post-conditions
    • The most important part of the contract.
    • The post-conditions are “ not” actions to be performed during the operation, rather they are declarations about the system state that are true when the operation has finished
    • The intension of the contract is to emphasize a declaration of state changes , but not telling how a solution to be achieved.
    • Use these categories of state changes in the post-conditions:
        • Instance creation and deletion.
        • Attribute modification.
        • Associations formed and broken.
  • 9. How to Make A Contract
    • Apply the following advice to create contracts.
    • To make contracts for each use case:
        • Identify the system operations from the system sequence diagrams.
        • For each system operation, construct an contract.
        • Start by writing the Responsibilities section, informally describing the purpose of the operation.
        • Then complete the Post-conditions section, declaratively describing the state-changes that occur to objects in the conceptual model.
        • To describe the post-conditions, use the following categories:
            • Instance creation and deletion.
            • Attribute modification.
            • Associations formed and broken.
        • The effect of the system operations is described in contracts.
  • 10. Contracts and other Artifacts – Ex : POST use case: Buy Item Actors Action
  • 11. Advice on Writing Contracts
    • After filling in the operation name, fill in the Responsibilities section first, pre-conditions section next, post-conditions last.
    • These are the most important sections likely to be used later in the project.
    • Use the Notes section to discuss any design details, such as algorithm or the high-level sequential steps.
    • Use the Exceptions section to discuss the reaction to exceptional situations.
  • 12. The Most Common Mistake in Creating Contracts
    • Don’t forget!
    • The most common problem is forgetting to include the forming of associations.
    • Particularly when new instances were created, it is very likely that associations to several objects needs to have been established.

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