Use-Case Model : Adding Detail with operation contracts

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Use-Case Model Adding Detail with operation
contracts

• Larman ch. 13

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UP artifacts
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Operation contracts

• Part of the use-case model
• Analyze technique
• Use cases are the primary mechanism in UP to
  describe system behavior
• Contracts help define system behavior
• Adds more details
• Contracts may not be needed.
• Objectives
• Define operation contracts with Post conditions
• Relate contracts to the Domain Model and the
  Use-Case Model.

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System operations handle system events
System events invoke systems Operations. The
System event makeNewSale invokes a System
operation called makeNewSale
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Contracts CO2 enterItem

• Operation
• Name of operation and parameters
• enterIOtem(itemID ItemID, quantity integer)
• Cross Refernce
• Optional use case this operation can occur within
• Use Cases Process Sale
• Preconditions
• Assumptions about the state of the system before
  execution of the operation
• There is a sale underway
• Postconditions
• The state of the objects in the domain model
  after completion of the operation
• A SalesItem instanse 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 ProductsSpecification,
  based on itemID match (association formed)

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Postconditions

• Describe changes in the state of objects in the
  domain model that are true when the operation has
  finished.
• They are not actions to be performed during the
  operation
• Postconditions fall into these categories
• Instance creation and deletion
• Attribute modification
• Associations (UML links) formed and broken.

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WHAT !!!

• Focus on WHAT must happen in terms of objects in
  the Domain Model.
• What instances can be created ?
• What associations can be formed ?
• What attribute can be modified ?
• Dont describe HOW it is archived.

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Contracts leads to.

• It is common to discover
• new conceptual Classes
• Attributes
• Associations
• Dont be limited to the prior definition of the
  Domain Model

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Guidelines Contratcs

• Identifying operations from the SSDs.
• For system operations that are complex and
  perhaps subtle in their results, or which are not
  clear in the use case, constructs a contract.
• To describe the postconditions, use the following
  categories
• Instance creation and deletion
• Attribute modification
• Associations formed and broken

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Postconditions past tense

• Notice that the statements are expressed in the
  past tense
• A SalesLineItem sli was created (instance
  operation)
• Sli was associated with the current Sale
  (association formed)

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NextGen POS example

• P. 185-186

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UML operations

• UML operation
• An operation is a specification of a
  transformation or query that an object may be
  called to execute
• A method is an implementation of an operation.
• An UML operation has a
• Signature
• Operation specification ( describes the effects
  produced by executing the operation (that is the
  postconditions.
• Uses Pre- and Postconditions

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Artifact relationships