? Use Case -What are the domain processes ?

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Summary from previous lectures

• ? Use Case -What are the domain processes ?
• Use Case Diagram
• ? Conceptual Model -What are the domain concepts,
  terms ?
• Class Diagram (conceptual)
• classes, associations, attributes

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Fig 10.1 Summary from previous lectures
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System Sequence Diagrams

• Chapter 10
• Applying UML and Patterns
• -Craig Larman

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Introduction
Todays lecture

• Class diagrams represent static relationships.
• What about modeling dynamic behavior?
• Interaction diagrams(Sequence and communication
  diagrams) model how groups of object collaborate
  to perform some behavior
• Typically captures the behavior of a single use
  case

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System Sequence Diagram (SSD)

• For a use case scenario, an SSD shows
• The System (as a black box)
• The external actors that interact with System
• The System events that the actors generate
• SSD shows operations of the System in response to
  events , in temporal order
• Develop SSDs for the main success scenario of a
  selected use case, then frequent and salient
  alternative scenarios

System
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Identifying the right Actor

• In the Process Sale example, does the customer
  interact directly with the POS system?
• Who does?
• Cashier interacts with the system directly
• Cashier is the generator of the system events

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Fig 10.2 SSD for a Process Sale scenario
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Relationship between SSD and Use case

• System Sequence Diagrams
• ? Draw a line representing the system as a black
• box.
• ? Identify each actor that directly operates on
  the
• system. Draw a line for each such actor.
• ? From expanded use case identify system
• events that each actor generates.Illustrate
  them.
• ? Optionally include use case text on left.

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Fig 10.3 Relationship between SSD and Use case
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Naming System events operations

• System events and associated system operations
  should be expressed at the level of intent.
• Rather than physical input medium or UI widget
• Start operation names with verb (from use case)
• Which is better, scanBarCode or enterItem?

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Fig 10.4 Naming System events operations
Capture the intent of the operation while
remaining abstract
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Fig 10.5 SSD for play Monopoly Game scenario
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SSDs and the Glossary in parallel

• Why is updating the glossary important when
  developing the SSD?
• New terms used in SSDs may need explanation,
  especially if they are not derived from use cases
  
• A glossary is less formal, easier to maintain and
  more intuitive to discuss with external parties
  such as customers

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Why Draw SSD?

• Important to know the system events.
• Sequence diagrams help the designer to determine
  how the system will react to each event.
• Need to design the software to handle these
  events and execute a response.

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Example 1
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Questions ?