Use Case Analysis – continued

1. Use Case Analysis – continued Control Classes Building Analysis Classes (Modified considerably by your Instructor)

2. Control Classes • A Control Class is a class used to model control behavior specific to one or more use cases. • Control classes encapsulate use-case-specific behavior. • The behavior of a control object is closely related to the realization of a specific use case. • In many scenarios, you might even say that the control objects "run" the use-case realizations. • Some control objects can participate in more than one use-case realization if the use-case tasks are strongly related. • Similarly, some use cases may require more than one control class; but in general, there is a one-to-one correspondence – as a heuristic.

3. <<control>> What is a Control Class? • Use-case behavior coordinator • One control class per use case Analysis class stereotype Use Case Use-case dependent, Environment independent

4. Control Classes – not always needed • Control classes provide coordinating behavior in the system. • The system sometimes can perform some use cases without control classes (just using entity and boundary classes) – particularly use case only involves simplemanipulation of stored information. • Complex use cases generally require one or more control classes to coordinate the behavior of other objects in the system. •  Examples of control classes include • transaction managers, • resource coordinators and • error handlers.

5. Control Classes decouple: • Control classes effectively decoupleboundary objects from one another, making the system more tolerant of changes in the system boundary. • They also decouple the use-case specific behavior from the entity objects, making them (the entity objects) more reusable across use cases and systems. • Note: we are in the initial stages of ‘design’ • Decoupling may positively affect some of the non-functional requirements (that are addressed in design in considerable detail), such as maintainability, performance, reusability. • Discuss: (A number of non-functional requirements are quite contradictory in places…)

6. Control Class provided behavior: • Is surroundings-independent (does not change when the surroundings / environment change) • Defines control logic • Orderthe sequence of activities to realize the use-case. (Consider registering for courses…. • Changes little if the internal structure or behavior of the entity classes changes • Use or set the contents of several entity classes, and therefore needs to coordinatethebehavior of these entity classes (gets and sets and sequencing…) • Is not performed in the same way every time it is activated (flow of events features several states) •  One recommendation for the initialidentification of control classes is one control class per use case.

7. <<boundary>> <<control>> <<boundary>> Customer <<boundary>> <<entity>> <<entity>> Coordinate the use-case behavior The Role of a Control Class Database • Several control objects of different control classes can participate in one use case. • As stated, not all use cases require a control object. • Example: if the flow of events in a use case is related to one entity object, • a boundary object may realize the use case in cooperation with the entity object. • You can start by identifying one control class per use caserealization, and then • refine this as more use-case realizations are identified and commonality is discovered.

8. Role of Control Class • Control classes contribute to understanding the system. • Represent the dynamics of the system, • Hande the main tasks and control flows. • When the system performs the use case, a control object is created. • Control objects usually die when their corresponding use case has been performed. • (Normally NOT persistent)

9. Student Register for Courses Course Catalog System <<control>> RegistrationController Example: FindingControlClasses • Recommend: Identify one control class per use case (again) Each control class is responsible for orchestrating/controlling the processing that implements the functionality described in the associated use case. Here, the RegistrationController <<control>> class has been defined to orchestrate the Register for Courses processing (sequencing of activities) within the system.  (Controller accepts inputs, ‘knows’ where required data and functionality reside, sends key messages to entities, sequences all actions to satisfy use case, sends data back to input actor, etc….)

10. Summary of Analysis Classes: View of Participating Classes (VOPC) • For each use-case realization there is one or more class diagrams depicting its participating classes, along with their relationships. • Such class diagrams have been called “View of Participating Classes” diagrams (VOPC, for short) – next overhead…

11. Register for Courses Student <<entity>> CourseOffering <<boundary>> RegisterForCoursesForm <<control>> RegistrationController <<boundary>> CourseCatalogSystem <<entity>> Student <<entity>> Schedule Example: Summary: Analysis Classes - VOPC • The diagram here shows the classes participating in the Register for Courses use case • The part-time student and full-time student classes have been omitted for brevity (they both inherit from Student. Class relationships will be discussed later. Course Catalog System Use-Case Model Design Model (classes only listed – no relationships shown here…)

12. Use-Case Analysis Steps – Next Major Step… • Supplement the Use-Case Descriptions • For each use-case realization • Find Classes from Use-Case Behavior - DONE! But nothing in them! •  Distribute Use-Case Behaviors to these Classes Now we need to allocate responsibilities of the use cases to the analysis classes and model this allocation by describing the way the class instances collaborate to perform the use case in use-case realizations. Purpose of Distributing Use Case Behavior to Classes is to: • Express the use-case behaviorin terms of collaborating objects, and thus • Determine the responsibilities of analysis classes. •  For each resulting analysis class, do: • Describe Responsibilities • Describe Attributes and Associations (lectures ahead and following…) • Qualify Analysis Mechanisms (more coming on this last item)

13. Collaboration Diagrams Sequence Diagrams Distribute Use-Case Behavior to Classes • For each use-case flow of events: • Identify analysis classes (Step thru flow of events) • We have identified classes. Now, see where they are applied in the use case flow of events. • Static: Allocate use-case responsibilities to analysisclasses (look for the verbs and actions in use case flow…) • Dynamic: Model analysis class interactions in interaction diagrams we need to show interactions of system with its actors. •  Interactions all begin with an actor, who invokes the use case (Use cases don’t start themselves!) Use Case Use-Case Realization

14. Interactions among Actors? No. • Interactions BETWEEN actors should NOT be modeled. (Can show inheritance, surrogates, etc. but no ‘interactions.’) • By definition, actors are external, and are out of scope of the system being developed. • Thus, you do not include interactions between actors in your system model. • Let’s look at how to distribute behavior to classes:

15. Guidelines: Allocating Responsibilities to Classes • This allocation of responsibilities is crucial! • Stereotypes assist in that they provide a set of canned responsibilities that we can use. • Use analysis class stereotypes as a guide • Boundary Classes (the Interface) • Behaviors that involves communication with an actor • Entity Classes (Persistent Data) • Behaviors that involves the data encapsulated within the abstractions. (All data manipulation, retrieval…) • Control Classes (the Use Case flow of events) • Behaviors specific to a use case or part of a very important flow of events (continued)

16. Guidelines: Allocating Responsibilities to Classes (cont.) • A driving influence on where a responsibility should go is the location of the data needed to perform the operation. • Who has the data needed to perform the responsibility? • Example: “System displays Patient data on monitor.” • OK. Where is the patient data? – patient object. • Who can ‘get’ the data? Patient object! (may imply a retrieval from a database, but ultimately the patient object has the data and the responsibility to get it.)

17. Guidelines: Allocating Responsibilities to Classes (cont.) • Design options: • For a class that has the data, put the responsibility for access, for manipulation, for modification, etc. with the data – best case!!! • If Multiple classes have the data: • Put the responsibility with one class and add a relationship to the other (a dependency relationship) • Create a new class, put the responsibility in the new class, and add relationships to classes needed to perform the responsibility • Put the responsibility in the control class, and add relationships to classes needed to perform the responsibility

18. Guidelines: Allocating Responsibilities to Classes (cont.) • Be careful when adding relationships -- all relationships should be consistent with the abstractions they connect. •  Don’t just add relationships to support the implementation without considering the overall affect on the model. •  When a new behavior is identified, check to see if there is an existing class that has similar responsibilities, reusing classes where possible. •  Only when sure that there is not an existing object that can perform the behavior should you create new classes.