Agenda

• Analyze a Use Case
• Goals for Use Case Realization
• What Are Use Case Realizations?
• Interactions
• Lifelines and Messages
  • Add Course Use Case
  • Delete Course Use Case
• Combined Fragments and Operators
• Communication Diagrams

Analyze a Use Case

• Analysis classes model the static structure of a system, and use case realizations show how instances of the analysis classes interact to realize the functionality of the system.
• This is part of the dynamic view of the system.

Goals for Use Case Realization

• Find out which analysis classes interact to realize the behavior specified by use cases-you may uncover new analysis classes as you perform use case realization
• Find out what messages instances of these classes need to send to each other to realize the specified behavior. This tells you
  • the key operations your analysis classes need to have
  • the key attributes of the analysis classes
  • important relationships between analysis classes
  • Update your use case model, requirements model, and analysis classes with the information you get from use case realization. Keep all models consistent and in step with each other.

What are use case realizations?

• Use case realizations show how classes collaborate to realize system functionality.
  • Analysis class diagrams "tell story" about one or more use cases
  • Interaction diagrams show how classifier instances interact to realize system behavior.
• You turn a use case, which is a specification of functional requirements,  into a class diagram and interaction diagram, which are a high-level specification of the system.

Each use case has exactly one use case realization, so instead you add appropriate elements as listed in the table below.

Interactions

• Interaction - a unit of behavior of a context classifier
• In use case realization a context classifier is a use case.
• You create one or more interactions to demonstrate how behavior specified by the use case can be realized by instances of classifiers (either in in the analysis-analysis classes, or in the design-design classes) passing messages back and forth.

Add Course Use Case

Interaction diagrams are not verbatim transcriptions of a use case; they are illustrations of how the use case behavior is realized by analysis classes.

Delete Course Use Case

State Invariants and Constraints

You can show the state of the instances on the lifelines by using state invariants.
Adding state invariants to a sequence diagrams can be a very useful analysis technique because it allows you to capture the key states in the lifecycle of  a lifeline.

Capture the following constraints:

• the order must be paid for in full by a single payment
• the items specified in the order can only be delivered after payment
• the items are delivered to the customer within 28 days of payment