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Operation Contracts: Getting ready to open the “System” black box

Operation Contracts: Getting ready to open the “System” black box. All material from Applying UML and Patterns, 3 rd Edition, Craig Larman, chapter 11. Operation Contract.

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Operation Contracts: Getting ready to open the “System” black box

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  1. Operation Contracts: Getting ready to open the “System” black box All material from Applying UML and Patterns, 3rd Edition, Craig Larman, chapter 11.

  2. Operation Contract • Considered part of the Use Case Model because they provide more analysis detail on the effect of the system operations implied in the use cases

  3. Operation Contracts • Define the effect of the system operations on the domain model objects

  4. System Operations • Operations that the system as a black box offers in its public interface

  5. Public System Interface • The entire set of system operations across all use cases defines the public system interface, viewing the system as a single component or class.

  6. System Operations • Prime inputs to the contracts are the system operations identified in SSDs and the domain model • Contracts in turn serve as input to the object design as they describe changes that are likely required in the software objects or database.

  7. Fig. 11.1

  8. System Operations • Can be identified in SSDs

  9. Operation Contracts Text, Figure 11.2

  10. Sections of an Operation Contract • Operation: Name of the operation and parameters • Cross References: Use cases and scenarios this operation can occur within • Preconditions: Noteworthy assumptions about the state of the system or objects in the Domain Model before execution of the operation. • Postconditions: This is the most important section. The state of objects in the Domain Model after completion of the operation

  11. Postconditions: most important • Describe changes in the state of objects in the domain model after completion of the operation • what instances were created ? • what associations were formed/broken? • what attributes changed? • Are not actions to be performed during the operation

  12. Examples of Operation Contracts from Process Sale Use Case (Fig.11.9)

  13. Operation Contract for makeNewSale operation • Operation: makeNewSale() • Cross References: • Use Case: Process Sale • Scenario: Process Sale • Preconditions: none • Postconditions • a sale instance “s” was created (instance creation) • s was associated with the Register (association formed) • attributes of s were initialized

  14. What this looks like: s:Sale was created association was created attributes of s:Sale were initialized

  15. Example—Operation Contract for enterItem operation • Operation: enterItem(itemID,quantity) • Cross References: • Use Case: Process Sale • Scenario: Process Sale • Preconditions: There is a sale underway.

  16. Example—Operation Contract for enterItem operation • Postconditions: • A salesLineItem instance sli was created (instance creation) • sli was associated with the current Sale (association formed) • sli.quantity became quantity (attribute modification) • sli was associated with a ProductDescription, based on itemId match (association formed)

  17. What this looks like: associations were created sli:SalesLineItem was created sli.quantity was initialized to input quantity

  18. Example—Operation Contract for endSale operation • Operation: endSale() • Cross References: • Use Case: Process Sale • Scenario: Process Sale • Preconditions: There is a sale underway • Postconditions • s.isComplete became true (attribute modification)

  19. What this looks like: s.isComplete became true

  20. Example—Operation Contract for makePayment operation • Operation: makePayment(amount:Money) • Cross References: • Use Case: Process Sale • Scenario: Process Sale • Preconditions: There is a sale underway

  21. Example—Operation Contract for makePayment operation • Postconditions • a payment instance “p” was created (instance creation) • p.amountTendered became amount (attribute modification) • p was associated with s:Sale (association former) • s:Sale was associated with the Store (association formed)

  22. What this looks like: associations were created p:Payment was created p.amountTendered was initialized to input amount

  23. Why Operation Contracts? • An excellent tool of OO requirements analysis that describes in great detail the changes required by a system operation (in terms of the domain model objects) without having to describe how they are to be achieved • Excellent preparation for opening the System black box!

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