Larman chapter 61 Use cases Larman chapter 6

2 Fig. 6.1

Larman chapter 63 What are actors, scenarios and use cases? Use cases are stories of how actors use the system to fulfill his goal E.g. “ process sale” actor: a person or a system with behavior There are different kinds of actors: those who uses our system and those who is used by our system. –A “cashier” uses our system –A “tax calculator” is used by our system

Larman chapter 64 What are actors, scenarios and use cases? Primary actor –Has user goals fulfilled through using the services of the system Supporting actor –Provides a service (for example information) to the system Offstage actor –Has an interest in the behavior of a use case, but is not primary or supporting (e.g. tax agency)

Larman chapter 65 What are actors, scenarios and use cases? A scenario is a specific sequence of actions and interactions between an actor and the system. A use case is a collection of related success and failure scenarios Focus : –Describe actions that gives the actor observable value, not only a list of functions that the system offers. –Describe what, not how.

Larman chapter 66 What are actors, scenarios and use cases? Use-cases are text documents, not diagrams. Use Case modeling is primarily an act of writing text, not drawing diagrams

Larman chapter 67 use-case types and formats Black-box use case –Most common and recomended –They do not describe the internal working of the system. –The system is desribed as having responsibilities. Formats –Brief (page 63) Terse one-paragraph summary, usually the main success scenario –Casual Informal, multiple paragraphs that cover various scenarios –Fully dressed (page 68-72) The most elaborate. All steps and variations are written in detail and there are supporting sections with preconditions etc.

Larman chapter 68 Use case sections- fully dressed format Scope Level Primary actor Stakeholders and interests Precondition and success guaranties Main success scenario and steps Extensions Special requirements Technology and data variations list Frequency of occurrence Open issues

Larman chapter 69 Evaluation – what is a proper use case Use cases for elementary business processes (EPB) a task performed by one person in one place at one time, in response to a business event, which add measurable business value and leaves the data in a consistent state. E.g. ‘approve credit’ or ‘price order’ or ‘process sale’

Evaluation – what is a proper use case The Boss test –Your boss asks, “what have you been doing all day?” –What makes your boss happy? The Size test –A use case is seldom a single action/step! Larman chapter 610

Larman chapter 611 Use cases and goals Recommended procedure: –Find the user goals –Define a use case for each How? –Ask: what are your goals? (Instead of what do you do?)

Larman chapter 612 Finding primary actors, goals and use cases 1.Choose the system boundary 2.Identify the primary actors 3.For each, identify their user goals 4.Define use cases that satisfy user goals, name them according to their goal (guidelines on p 81 – 89)

Larman chapter 613 Fig. 6.2

Larman chapter 614 Use case diagram

Larman chapter 615 Fig. 6.4

Larman chapter 616 Fig. 6.5

Larman chapter 617 Fig. 6.6

Larman chapter 618 Fig. 6.6

Larman chapter 619 Fig. 6.7