Object Oriented Analysis and Design
Using the UML
Use Case Analysis
Modified considerably by your Instructor
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Objectives: Use-Case Analysis
Understand the purpose of Use-Case Analysis and where in the lifecycle it is performed
Identify the classes needed to accommodate a use- case flow of events (Analysis Classes)
Distribute the use-case behavior to those classes, identifying responsibilities of the classes
The analysis classes and the initial use-case realizations are the key model elements that we develop in this
activity.
Use Case Analysis
The focus during Use-Case Analysis is on a particular use case.
In Use-Case Analysis, we identify the analysis classes and define their responsibilities.
(At this time, we speak of ‘responsibilities.’ (May even use the term, ‘services.’) Later, these might
become ‘methods’ or ‘member functions.’ But that is a matter for implementation NOT initial design.)
The allocation of responsibility is modeled in use- case realizations that describe how analysis
classes collaborate to perform (realize) use cases.
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Supplementary
Specifications Glossary
Use-Case Model
Use-Case Analysis
Use-Case
Modeling Guidelines
Use-Case Realization (developed)
Design Model Analysis Classes
Analysis Model (optional)
Use-Case Analysis Overview
Software Architecture Document – (don’t
really have this one yet.)
Use Case Analysis is performed By the Designer – once per
Iteration per use case realization
Use Case Analysis - Purpose
To identify analysis classes which perform a use case’s flow of events
To distribute the use case behavior to those classes
To identify the responsibilities, attributes and associations of the classes
Input Artifacts – see previous slide
Output Artifacts:
Analysis Classes
Analysis Model
Partially Developed Use-Case Realizations
Work toward Design Model (first cut, really)
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Use-Case Analysis Steps – Major ones
1. Supplement the Use-Case Description
Will be changing some as we continue to examine our Use Cases and add alternative, exception, and other flows.
We modify as we learn more and analyze…
2. For each use-case realization, Do:
Study Use Case flow of events - identify analysis classes from the Use Case narrative. These consist of interface, control, & data classes.
Allocate behaviors (responsibilities) to these classes.
• These are the little things the class must do….in some cases, these are merely options afforded to the user like add new customer() or delete customer ()….
Distribute Use-Case Behaviors to Classes that you identify
Describe Attributes (properties) of each analysis class.
Show associations between the collaborating classes.
Let’s look at each of these two major items in particular….
Use-Case Analysis Steps
1. Supplement the Use-Case Description
Capture additional information in order to understand the required internal behaviors.
It is quite customary to make changes (or should be….)
This is part of the iterative process. Versioning of Use Cases.
This is why we spend so much time on getting those use cases right – recall, Use Cases drive the whole shooting match!
Update / collapse flows of events as needed…..(also Activity Diagrams)
But this is difficult to do. Consider
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• The system displays a list of
course offerings.
• The system retrieves and displays a list of current course offerings from the course catalog legacy database given specific parameters, such
as...
Supplement the Use-Case Description
Sometimes the
description of the use case is not sufficient for identifying analysis
classes and their objects.
Remember, customer doesn’t care about the inside of the system, so many details may have been left out – leaving the use case description like a black box.
Many times we do not have
enough detail.
1. Supplement the Use-Case Description
2. For each use-case realization, Do:
Find Classes from Use-Case Behavior
May be easier now to identify our candidate analysis classes for the system
• (candidate means ‘first cut;’ ‘possible’ classes)
• Identify a set of candidate analysis classes
capable of performing the behaviors (actions;
‘verbs’) described in the use case.
• These are ‘responsibilities’ of these classes.
Use-Case Analysis Steps
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Find Candidate Classes from Behavior (1 of 2)
Will use three ‘division of responsibilities’ of the system to identify these classes.
Look for Classes that form:
The ‘boundary’ between the system and its actors
The ‘information’ the system uses
The ‘control logic’ of the system
Will use ‘stereotypes’ to represent these classes.
(These are conveniences used during analysis some of which will disappear or be transitioned into different design elements during the design process.)
This leads to a more robust design, as these things are likely to change during design. This way we can isolate them
according to their use in the application.
<<boundary>>
<<boundary>>
<<control>>
<<entity>>
<<entity>>
Find Classes From Use-Case Behavior
The complete behavior of a use case must be distributed to analysis classes
We must ‘identify’ these classes – give a name and briefly describe what they do in a few
sentences.
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Kinds of Analysis Classes
The boundary between the system and its actors (interfaces… to end-users, external systems, devices…)
The information a system uses (data), and
The control logic of the system (who does what)
So, we isolate the different kinds of concerns and use analysis classes to capture these
responsibilities.
Each category of analysis class has a typical
set of duties & responsibilities
<<control>>
<<boundary>>
<<entity>>
System boundary
Use-case behavior coordination
System information
What is an Analysis Class?
Can use with the name of the stereotype
In angle brackets or as symbols with unique icons.
Finding a candidate set of classes is the first part of transforming a mere statement of
required behavior to a description of how the
System will work. So, we start with Analysis Classes.
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Analysis Classes – an Early Conceptual Model
The analysis classes, taken together, represent an early conceptual model of the system.
This conceptual model evolves quickly and remains fluid for some time as different
representations and their implications are
explored. (Consider boundary classes that form a user interface…)
Analysis classes rarely survive into the design unchanged. (But some do!) Don’t spend a lot of time here.
Analysis classes allow us to play with distribution of responsibilities some of which will be later reallocated.
Many of them represent whole collaborations of objects, often encapsulated by a single
subsystems or a reverse engineered component,
such as the user interface GUI.
Use Cases Analysis Classes
Source Code
Exec Design
Elements
Use-Case Analysis
Analysis Classes: A First Step Towards
Executables
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<<boundary>>
Analysis class stereotype
What is a Boundary Class?
Insulates the system from changes in the outside
Three types of Boundary Classes
1. User interface classes – classes that facilitate communication with human users of the system
• Menus, forms, windows, etc. User interface classes….
2. System interface classes – classes which facilitate communications with other systems. Very Important!
• These boundary classes are responsible for managing the dialogue with the external system, like getting data from an existing database system or flat file…
• Provide an interface to that system (like a VSAM file)
3. Device Interface Classes – provide an interface to devices which detect external events – like a sensor or …
One boundary class per use case/actor pair
Customer
<<boundary>>
<<boundary>>
<<control>>
<<boundary>>
<<entity>> <<entity>>
The Role of a Boundary Class
• Boundary class - used to model interaction between system’s surroundings and its inner workings.
• Boundary Classes model parts of the system that depend on its surroundings.
• Entity and control classes model parts that are independent of system’s surroundings.
. Examples of boundary classes: Classes that handle GUI or communications protocols.
• Actors can only communicate with boundary classes.
• Boundary classes identify the system’s boundaries.
External Database
<< boundary>>
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Boundary Classes - more
Identify boundary classes for actor
interactions mentioned in the flow of events of the use-case
Consider the source for all external events and make sure there is a way for the system to detect these events (user inputs/responses,
connecting to an external file, detecting a buzzer, etc.
Heuristic: initial identification of boundary classes: one boundary class per actor/use- case pair.
Course Catalog System Register for Courses
Student
<<boundary>>
RegisterForCoursesForm
<<boundary>>
CourseCatalogSystem
Example: Finding Boundary Classes
One boundary class per actor/use case pair:
•The RegisterForCoursesForm contains a Student's "schedule-in-progress". It interfaces with the actor and displays a list of Course Offerings for the current semester from which the Student may select specific courses to be added to his/her Schedule. (Note that this description comes directly from the use case specification. We capture that behavior and encapsulate it (for now) into a boundary class with this description.)
•The CourseCatalogSystem interfaces with the legacy system that provides the
Two boundary classes:
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Boundary Class – As a User Interface classes
1. Concentrate on what information is presented to the user
Do NOT concentrate on the UI details (windows, forms…)
Analysis Classes are meant to be a first cut at the abstraction of the system.
The boundary classes may be used as ‘holding places’ for GUI classes. (Addressed in more detail later in design)
Do not do a GUI design in analysis, but isolate all
environment-dependent behavior. (Likely you may be able to reverse engineer a GUI component and tailor it.)
If prototyping the interface has been done, these screen
dumps or sketches may be associated with a boundary class.
Only model the key abstractions of the system – not every button, list, etc. in the GUI.
Boundary Classes – As External System and Device classes
2-3. System and Device Interface Classes
Concentrate on what protocols must be defined
• Note that your application must interface with an existing information source, like a RDBMS...
Do NOT concentrate on how the protocols will be implemented! Merely note that there is an interface.
If the interface to an existing system or device is already well-defined, the boundary class responsibilities should be derived directly from the interface definition.
If there is a working communication with the external
system or device, make note of it for later reference
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Glossary
Business-Domain Model
Environment Independent
<<entity>>
Analysis class stereotype
Use Case
Architectural Analysis Abstractions
What is an Entity Class? (recall:
boundary, entity, control…)
Key abstractions of the system
(What does that mean?)Entity classes show the logical data structure, which will help us
understand what the system is supposed to offer to its users.
Sources for entity Classes:
Glossary
Use-Case Flow of Events
Domain Model
things……
Entity Classes
Represent stores of information in the system
Used to represent the key concepts the system manages. (Core Abstractions)
The main responsibilities of entity classes are to store and manage information in the system.
Entity objects (instances of entity classes) hold and update information on some phenomenon, such as an event, a person, or some real-life object.
(Chapter advisor, memorabilia, university, student,
correspondence_item, International_Secretary, Provider, Worker, account, inventory-item, …)
What are the ‘nouns’ in the use-case specification??
Often persistent; may well come from domain model
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Customer
<<boundary>>
<<boundary>>
<<control>>
<<boundary>>
<<entity>> <<entity>>
The Role of an Entity Class
Entity objects are usually not specific to one
use-case realization;
The values of an entity object and their relationships are often given by an actor.
Entity objects are independent of the environment (actors)
Entity objects can have complicated behavior;
however, unlike other objects, this behavior is strongly related to the phenomenon the entity object represents.
Example: Finding Entity Classes
Use use-case flow of events, the domain model, and glossary as inputs.
The more of these you have the better you are!
Traditional, filtering nouns approach (but I’d
recommend using classes from the domain model (business entities) as a starting place, if available)
Underline noun clauses in the use-case flow of events
Remove redundant candidates; Lots of synonyms!
Remove vague candidates
Remove actors (out of scope)
Remove implementation constructs
Remove attributes (save for later)
• Lots of times, candidate ‘nouns’ may become ‘attributes’
in classes.
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Student
CourseOffering
Schedule
Example: Candidate Entity Classes
Register for Courses Use Case
Specific scenario? Likely, Create Schedule.
A specific offering for a course including days of week and times
The courses a student has selected for current semester
Note: these are candidate entity classes only. So far, they do not possess responsibilities, attributes, associations, etc…
A person enrolled in classes at the university
Candidate Entity Classes – Actors – same name?
Sometimes there’s a need to model
information within the system. This is not the same as modeling the actor (actors are
external. by definition) with the same name.
A course registration system maintains
information about the Student object which is independent of the fact that the Student also plays a role as an Actor of the system.
Completely independent of each other
Student class (entity) will exist whether or not the
student is an actor to the system.
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Account balance
name number Withdraw()
CreateStatement()
Checking Withdraw()
Savings GetInterest() Withdraw()
Superclass (parent)
Subclasses
Generalization Relationship
Review: Generalization (in entity classes)
One class shares the structure and/or behavior of one or more classes
“Is-a-kind of” relationship
In analysis, use sparingly
Inheritance relationships may be identified – especially in entity classes.
In analysis, generalization should be used to model shared behavioral
semantics only (that is, generalization that passes “is a kind of’ test)
The use of generalization makes the definition of the abstractions easier to document and understand.
When generalization is found, create a common super-class that contains common attributes associations, aggregations, and
Student name address
FulltimeStudent
studentID
gradDate
ParttimeStudent maxNumCourses
Part-timeStudent
name address
numberCourses
Full-timeStudent
name address studentID gradDate
Without
Generalization
With
Generalization
studentID
