Use Case Analysis – continued
Control Classes
Building Analysis Classes
(Modified considerably by your Instructor)
OOAD Using the UML - Use-Case Analysis, v 4.2
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Control Classes
 A class used to model control behavior specific to
one or more use cases.
 Encapsulate use-case-specific behavior.
 Behavior of a control object is closely related to the
realization of a specific use case.
 Might ‘say’ 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.
OOAD Using the UML - Use-Case Analysis, v 4.2
Copyright  1998-1999 Rational Software, all rights reserved
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What is a Control Class?
 Is a Use-case behavior coordinator;
 sequences; controls; orchestrates use-case.
 One control class per use case (generally)
<<control>>
Use Case
Analysis class
stereotype
Use-case dependent, Environment independent
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Copyright  1998-1999 Rational Software, all rights reserved
3/18
Control Classes – not always needed
 Provides 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 simple
manipulation 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. Think about these activities!!
OOAD Using the UML - Use-Case Analysis, v 4.2
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4/18
Control Classes decouple:
  Decouple boundary objects from one another,
making the system more tolerant of changes in the
system boundary.
 Boundary objects may be several; can make cohesive,
separate, easy to change / modify…
  Also decouple from control classes use-case
behaviors to 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 nonfunctional requirements (that are addressed in design in
considerable detail), such as maintainability,
performance, reusability.
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Control Class provided behavior:
 Surroundings-independent (does not change when
the surroundings / environment change)
 Define control logic
 Order/Direct sequence of activities to realize the usecase. (Consider Registering for Courses use case….
 Changes little if the internal structure or behavior of the
entity classes changes
 Control Classes use or set the contents of entity
classes, and thus need to coordinate behaviors
of entity classes
 Is not performed in the same way every time it is
activated (flow of events features several states)
  One recommendation for the initial identification
of control classes is one control class per use case.
OOAD Using the UML - Use-Case Analysis, v 4.2
Copyright  1998-1999 Rational Software, all rights reserved
6/18
The Role of a Control Class
<<boundary>>
<<control>>
<<boundary>>
Customer
Database
<<boundary>>
<<entity>>
<<entity>>
Coordinate the use-case behavior
• Several control objects of different control classes can participate in one use case
This is particularly true if the use case is rather complex and requires much
coordination of access of entity objects, etc.
• As stated, not all use cases require a control object but most do – at least one.
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 case realization, and then
OOAD Using the UML - Use-Case Analysis, v 4.2
refine
this as more use-case realizations are
identified and commonality is discovered.
Copyright  1998-1999 Rational Software, all rights reserved
7/18
Role of Control Class and Control Objects
 Control classes contribute to understanding
the system.
 Represents the dynamics of the system,
 Handles the main tasks and control flows.
 When the system performs the use case, a
control object is created.
 Control Objects usually die once their
corresponding use case or scenario (story)
has been performed.
 (Normally NOT persistent)
8/18
OOAD Using the UML - Use-Case Analysis, v 4.2
Copyright  1998-1999 Rational Software, all rights reserved
Example: Finding Control Classes
 Recommend: Identify one control class per use case (again)
Student
Register for Courses Course Catalog System
<<control>>
RegistrationController
 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 via boundary objects, etc….)
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Now, Summarizing Analysis Classes in general:
 Summary of Analysis Classes: View of Participating
Classes (VOPC)
 For each use-case realization (note the loop)
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…
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Example: Summary: Analysis Classes - VOPC
• The diagram 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.
Student
Register for Courses
Course Catalog System
Use-Case Diagram
Analysis Model (classes only listed – no relationships shown here…)
<<boundary>>
RegisterForCoursesForm
<<entity>>
Student
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<<control>>
RegistrationController
<<entity>>
Schedule
11/18
<<boundary>>
CourseCatalogSystem
<<entity>>
CourseOffering
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 behavior in terms of collaborating
objects, and thus
 Equivalently: Determine the responsibilities of analysis classes.
 



For each resulting analysis class, do: (see loop?)
Describe Responsibilities (behaviors)
Describe Attributes and Associations (lectures ahead and following…)
Qualify Analysis Mechanisms (more coming on this last item; quality
metrics; non-functional requirements, such as persistence…)
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12/18
Distribute Use-Case Behaviors to Classes
 For each use-case flow of events: (Note:
this is a loop!!!)
 Identify analysis classes (Step thru flow of events)
 Have identified classes. Now, see where they are applied in the
use case flow of events.
 Static: Allocate use-case responsibilities to analysis classes
(look for the verbs and actions in use case flow…)
 Dynamic: Model analysis class interactions in interaction
diagrams  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
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Sequence Diagrams
Collaboration Diagrams
13/18
Use-Case Realization
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.
 How to distribute behavior to classes:
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Guidelines: Allocating Responsibilities to Classes
 This allocation of responsibilities is crucial!
 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
 Notice, all these allocations are of behaviors.
(continued)
OOAD Using the UML - Use-Case Analysis, v 4.2
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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.”
• Where is the patient data? Patient object. (entity 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.)
 Who coordinates (issues message to patient object) to get this
data? Control class.
 Once the data is ‘obtained,’ who will “display” the data to the
actor? Boundary class. Look for data and verbs and nouns!
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Copyright  1998-1999 Rational Software, all rights reserved
16/18
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:
• 1. Put the responsibility with one class and add a
relationship to the other (a dependency relationship)
• 2. Create a new class, put the responsibility in the new
class, and add relationships to classes needed to
perform the responsibility
• 3. Put the responsibility in the control class, and add
relationships to classes needed to perform the
responsibility
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Copyright  1998-1999 Rational Software, all rights reserved
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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.
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Copyright  1998-1999 Rational Software, all rights reserved
18/18