Week IV in SOS  Tuesday Project Time -- 4:15pm-5pm URL for project(s) due to Judy by Friday 5pm  Friday Paper  OOAD Handouts thru last Thursday (see web site) Lectures coming this week. Exam week V or VI.  Use Case Detail

Week IV, Today  Recap Use Cases, Part I -- Business Dynamics  Debrief Homework Use Case Diagram for EU-Lease  Structure the Use Case Model – refining: > and > use cases actor and use case generalization supplemental questions scoping iterations  Start Use Case Detail …  Tomorrow Continue Use Case Detail Derive the User Interface

3 Structure the Use Case Model

4  6 things to know about a Use Case model:  How do I discover Use Cases?  What a Use Case is NOT  Where does ‘Use Case’ fit in the development process?  What are the basic elements of a Use Case Model?  How do I draw a Use Case Model as a diagram?  After the basics, how do I refine the Use Case Model? Use Cases ~ recap from last time

5  There are four core elements of a Use Case model:  the system (boundary) the set of all use-cases specify a system in terms of its intended functions (functionality). This defines a firm boundary around the system, separating it from the outside world.  the actor someone or something outside the system (boundary) that interacts with the system  the use case a sequence of actions a system performs that yields an observable result of value to a particular actor.  the request a line of communication between actor and use-case -- typically an initiating 'transaction.' It crosses the system boundary. The Use Case Model ~ What are its parts called?

6 shown here as a Use Case Diagram The Use Case Model ~ What are its parts called?

7 writing up the Use Case... Initially, just the:  Use Case name: o For example, "Order Vehicle Model"  Use Case description, a brief statement of: 1.the nature of what the actor needs (the system) to do 2.the observable result of value to the actor For example, In “Order Vehicle Model” the actor wishes to... o add more vehicles of a particular model into EU-Rent’s vehicle inventory, o increase the model’s vehicle-count of vehicles owned.  More elements will be added to the documentation of a use case. (to be covered in a future lecture). Use Case documentation ~ the initial elements

8  For example Launch Auction [ includes: Write Letters ]...Begin the processing to dispose of an identified number of vehicles of a particular model. This involves: – recording a specific number of vehicles of a particular model as being "surplus." – producing letters to the "interested members," notifying each selected person of the auction and inviting the member to submit a bid. – recording an initial, zero-amount bid record for each selected/contacted member.

9 In addition to the associations between actors and use- cases, you can define special kinds of association between use-cases:  using UML's stereotype extensions: the > stereotype  using use-case & actor generalization / specialization used to describe a specific form of a more general use-case or actor. After the basics, how do I refine a Use Case Model?

10  UML has standard features to extend the language.  The Guillemet character denotes a stereotype extension. >  2 stereotype extensions are used to define relationships between Use Cases: >  Note: “UML trivia” ~ a Guillemet is a single symbol, not two ‘less-than’ or two ‘greater-than’ characters. Use Case refinement using UML stereotypes

11  Refine using > if you find you are repeating actions in two or more separate use-cases and you want to “factor out” the common actions into one use-case that can be used in many places.  For example, You may find that the "Check Balance" use-case in the ATM system also includes the step "System prints receipt." This can be factored out into a "Print receipt" use-case which is related to each of the including use-cases. The Use Case > example 1

12  Refine using > if you find you are repeating actions in two or more separate use-cases and you want to “factor out” the common actions into one use-case that can be used in many places.  For example, In EU-Rent's Inventory Management system, you will discover that two use cases include the functionality to produce a Rental Group summary. This common functionality can be factored out into a separate use-case that is then related to each of the including use-cases. The Use Case > example 2

13  Refine using > when you need to describe a conditional variation of a base case. The “extension points” will be defined in that base case.  For example, The third entry of an invalid PIN in a single session retains the card and triggers an activity in a security violation use-case.  This is used primarily to represent optional behavior, to handle exceptions. The Use Case > example 1

14  Refine using > when you need to describe a conditional variation of a base case. The “extension points” will be defined in that base case.  For example, A vehicle model is typically discontinued when there are no vehicles of the model currently owned by EU-Rent. When there are vehicles, there needs to be special handling (e.g., to dispose of those vehicles). The Use Case > example 2

15 Actor Generalization This is in the Workshop – let’s discuss it here (as a jump-start to the Workshop) read it there, too

16  Once identified, it can still be hard to decide whether a set of actor- system interactions is a single use-case or several use-cases. For example,...  Why wasn't prompting for the PIN and validating it a complete use-case? "Use cases emerge when you focus on the things of value that a system provides to an actor." ~ Kruchten  We focus on these 'valued outputs' by analyzing the 'Information Requirements' of the system, in two flavors: (1)the Information Queries providing critical outputs from the system (2)the Information Updates keeping the system data used in (1) current and correct Where do we go from here?

17  Once identified, it can still be hard to decide whether a set of actor- system interactions is a single use-case or several use-cases. For example,...  Consider the Use-Case from EU-Rent…. Why wasn't special handling (e.g., to dispose of those vehicles) a complete use-case?. Where do we go from here?

18 A word on use case 'supplemental questions'

19 A word on the S/E Process (& iterative development)  The S/E Process The Construction Phase builds the system in a series of iterations. You set up the iterations by selecting use cases for each, or dividing use cases into ‘scenarios’…. Release Early, Release Often! Inception Elaboration Construction 1 | 2 | 3 | … Transition