Lecture 16 9/11/15

Reminder - Semester 1 Continuous Assessment  In lab MS Excel Exam  Thursday 19 th November  Group 1 4-5pm - A to L  Group 2 5-6pm – M to Z

More practice Which actor initiates the entering of an order? The clerk.

More practice Which actor responds to an order being entered? The accounts system.

More practice Is the Accounts System actor a human? No, it’s an information system.

More practice Who starts off the getting of an address? The accounts system.

More practice Can the Accounts System cancel an order? No.

More practice Who is the passive actor during order entry? The accounts system.

More practice Who is the primary actor during order entry? The clerk.

“Includes” – aka “Uses Association”  The includes relationship occurs when you are describing your use cases and notice that some of them have common subflows  To avoid describing a subflow more than once in several use cases, you can extract the common subflow and make it a use case of its own  The new use case can then be included (used) by other use cases

More on Include  The relationships among the other use cases and this new extracted use case is an “includes relationship”  The includes relationship helps us avoid redundancy by allowing a use case to be shared  A base use case is dependent on the included use case(s); without it/them the base use case is incomplete

“Extends” relationship  the extends relationship means that one use case is similar to another use case but does a bit more or is more specialized  the base use case (the use case that is extended) is extended with additional behaviour by the extending use case  the extensions can be seen as optional functionality added to the base use case

UCD Example – Include and Extend Use Case Generalization Actor Generalization

Use Case Generalization  A parent use case may be specialized into one or more child use cases that represent more specific forms of the parent.  A child inherits all structure, behaviour, and relationships of the parent.  Children of the same parent are all specializations of the parent.  In an Order Management system, the use cases Phone Order and Internet Order share a lot in structure and behaviour.  A general use case Place Order is defined where that structure and common behaviour is defined.  The abstract use case Place Order need not be complete in itself, but it provides a general behavioural framework that the child use cases can then make complete.

Reminder – Actor Generalization  In the context of use case modeling the actor generalization refers to the relationship which can exist between two actors and which shows that one actor (descendant) inherits the role and properties of another actor (ancestor).  The generalization relationship also implies that the descendant actor can use all the use cases that have been defined for its ancestor.  When it comes to air travel, both a "Business Traveler" and a "Tourist" are "Passengers".  The fact that they are passengers allow them to have common behavior such as "Buy Ticket" but the fact that they are separate actors implies they can also have differences.  The "Business Traveler" might be able to "Redeem Business Miles" while the "Tourist" cannot.