Class Model

1
Class Model

• Lecture 7
• Spring 2004

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Source

• These slides are entirely based on Chapter 7 of
  your textbook. However useful, reliance on just
  one source has its problems
• Your textbook is not the ultimate authority.
• Different people use the same terms for different
  things.
• A project manager needs to be able to use with
  precision the right terms for a given audience.
• The term Structural Modeling is not generally
  accepted Class Model is preferred. Why?
• The terms Class and Object are often confused
• The book uses the term Operations most use the
  term Methods. Operations is better, but Methods
  is the standard
• Multiplicity symbols vary widely
• We owe CRC cards to Rebecca Wirfs-Brock.
• Her companys website is the source on CRC cards.
  
• CTTC challenge Find this website, download more
  information, and share it with the class.

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Objectives

• Understand the relationship between the class
  model and the use-case models
• Be able to create CRC cards, class diagrams, and
  object diagrams
• Understand the rules and style guidelines for
  creating CRC cards, class diagrams, and object
  diagrams
• Understand the process used to create CRC cards,
  class diagrams, and object diagrams

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Structural Models

• Structural models represent the things, ideas, or
  concepts, that is, the objects, contained in the
  application domain of the problem.

Text, page 188
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Structural Models

• One important thing to remember is that, at this
  stage of development, the structural model does
  not represent software components or classes in
  an object-oriented programming language, even
  though the structural model does contain analysis
  classes, operations, and relationships among the
  analysis classes. The refinement of these
  initial classes into programming level objects
  comes later.

Text, pages 188-189
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Structural Models

• Typically, structural models are depicted using
  CRC cards, class diagrams, and, in some cases,
  object diagrams

Text, page 189
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Classes, Attributes, and Operations

• A class is a general template that we use to
  create specific instances, or objects, in the
  application domain
• All objects of a given class are identical in
  structure and behavior but contain different data
  in their attributes

Text, page 189
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Classes, Attributes, and Operations

• An attribute of an analysis class represents a
  piece of information that is relevant to the
  description of the class

Text, page 189
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Classes, Attributes, and Operations

• An operation, is where the behavior of the class
  will be defined.
• In later phase, the operations will be converted
  to methods. However, since methods are more
  related to implementation, at this point in the
  development we use the term operation

Text, page 189
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Relationships

• Generalization
• AKO as in An hourly employee is a kind of
  employee
• Superclass - Subclass
• Classification
• Aggregation
• A-part-of
• Association
• Verb
• Should make semantic sense

Text, page 190
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ako
Text, page 194
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A Part Of
My diamond is black, the books is white.
Why the difference?
Health Team
Doctor
Nurse
Text, page 194
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Verb
Patient
Appointment
Schedules
Text, page 194
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CRC cards

• Class-Responsibility-Collaboration cards
• The textbook cites three sources
• D. Bellin and S.S. Simone, The CRC Card Book
  (Reading, MA Addison-Wesley, 1997)
• I. Graham, Migrating to Object Technology
  (Wokingham, England Addison-Wesley, 1995)
• B. Henderson-Sellers and B. Unhelkar Open
  Modeling with UML (Harlow, Englan
  Addison-Wesley, 2000)
• Rebecca Wirfs-Brock is generally recognized as
  having introduced them

Text, page 191
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CRC cards responsibilities

• Knowing responsibilities
• An instance typically knows the values of its
  attributes and its relationships
• An instance may be responsible for knowing other
  things as well
• Doing responsibilities
• Those things that an instance of class must be
  capable of doing

Text, page 191
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CRC cards collaborations

• Most use cases involve a set of several classes,
  not just one class.
• This set of classes forms a collaboration
• A collaboration is the set of classes involved a
  use case
• There is one for each use case

Text, page 191
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CRC cards collaborations

• Collaborations allow us to think in terms of
  clients, servers, and contracts
• A client object is an instance of a class that
  sends a request to an instance of another class
  for an operation to be executed
• A server object is instance that receives the
  request from a client object
• A contract formalizes the interactions between
  the client and server objects.

Text, page 192
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Anthropomorphism

• Pretending that the classes have human
  characteristics
• Also called The Animation Principle
• The idea is to use the CRC framework plus
  play-acting to help identify
• The classes
• Their attributes
• Their operations
• Their relationships

Text, page 192
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A Note on Sources

• The book here acknowledges several very important
  sources among these please note these three
• K. Beck and W. Cunningham, A Laboratory for
  Teaching Object-Oriented Thinking, Proceedings
  of OOPSLA, SIGPLAN Notices 24, no. 10 (1989)
  (Kent Beck, Ward Cunningham, together with Ron
  Jeffries, created Extreme Programming XP)
• C. Larman, Applying UML and Patterns An
  Introduction to Object-Oriented Analysis and
  Design (Englewood Cliffs, NJ Prentice Hall,
  1998) (Craig Larmans book, a classic, introduces
  domain modeling, iterative design, and the use of
  patterns to solve architectural problems)
• R. Wirfs-Brock, B. Wilkerson, and L. Wiener,
  Designing Object-Oriented Software (Englewood
  Cliffs, NJ Prentice Hall, 1990) (This is the
  book that put CRC cards on the map)

Text, page 192
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Elements of a CRC Card

• One per class
• Class name (a noun), ID, Type, description, list
  of associated use cases
• Lists the responsibilities (knowing and doing)
• Lists the collaborators (classes involved in the
  associated use cases)
• Lists the attributes (in back)
• Lists the relationships (in back)

Text, page 192
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Elements of a CRC Card
Text, page 193
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Elements of a CRC Card
Text, page 193
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Class Diagrams

• A CLASS
• Represents a kind of person, place , or thing
  about which the system will need to capture and
  store information
• Has a name typed in bold and centered in its top
  compartment
• Has a list of attributes in its middle
  compartment
• Has a list of operations in its bottom
  compartment
• Does not explicitly show operations that
  available to all classes

Class1
-attribute1
operation1()
Text, page 195
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Class Diagrams

• AN ATTRIBUTE
• Represents properties that describe the state of
  an object
• Can be derived from other attributes, shown by
  placing a slash before the attributes name
• The visibility of an attribute can be public (),
  protected (), or private (-)

attribute name/ derived attribute name
Text, page 195
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Class Diagrams

• AN OPERATION
• Represents the actions or functions that a class
  can perform
• Can be classified as a constructor, query, or
  update operation
• Includes parentheses that may contain parameters
  or information needed to perform the operation
• The operations that are available to all classes
  (e.g., create a new instance, return a value for
  a particular attribute, or delete an instance)
  are not explicitly shown within the class
  rectangle

operation name ()
Text, page 195
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Class Diagrams

• AN ASSOCIATION
• Represents a relationship between multiple
  classes, or a class and itself
• Is labeled using a verb phrase or a role name,
  whichever better represents the relationship
• Can exist between one or more classes
• Contain multiplicity symbols, which represent the
  minimum and maximum times a class instances can
  be associated with the related class instance

1.. verb phrase 0..1
Text, page 195
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Object Diagrams

• An instantiation of all or part of a class diagram

Text, page 199
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Creating CRC Cards and Class Diagrams

• Object Identification
• Create CRC Cards
• Examine Common Object Lists
• Role-Play the CRC Cards
• Create the Class Diagram
• Review the Class Diagram
• Incorporate Patterns
• Review the Model

Text, page 200-204
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Creating CRC Cards and Class Diagrams

• Textual Analysis (see Figure 7-6)
• Nouns classes
• Adjectives attributes
• Verbs operations and associations
• Common Object List
• Tangible things
• Incidents
• Interactions
• Patterns (see Figure 7-7)
• Collection of classes that solve recurring
  problems

• Object Identification
• Create CRC Cards
• Examine Common Object Lists
• Role-Play the CRC Cards
• Create the Class Diagram
• Review the Class Diagram
• Incorporate Patterns
• Review the Model

Text, pages 200-201
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Creating CRC Cards and Class Diagrams

• Object Identification
• Create CRC Cards
• Examine Common Object Lists
• Role-Play the CRC Cards
• Create the Class Diagram
• Review the Class Diagram
• Incorporate Patterns
• Review the Model

• Perform Textual Analysis on the Use Cases and
  other writings to identify candidate classes
• Each Use Case defines a collaboration, which is
  the collection of classes that interact in the
  use case
• Work on one collaboration at a time
• A class may belong to more than one collaboration

Text, pages 202-203
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Creating CRC Cards and Class Diagrams

• Object Identification
• Create CRC Cards
• Examine Common Object Lists
• Role-Play the CRC Cards
• Create the Class Diagram
• Review the Class Diagram
• Incorporate Patterns
• Review the Model

• What are the tangible things associated with the
  problem?
• What incidents and interactions take place in
  the problem domain?
• It is possible to uncover additional roles
  outside the use cases and other writings

Text, page 203
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Creating CRC Cards and Class Diagrams

• Object Identification
• Create CRC Cards
• Examine Common Object Lists
• Role-Play the CRC Cards
• Create the Class Diagram
• Review the Class Diagram
• Incorporate Patterns
• Review the Model

• Each CRC card should be assigned to an
  individual, who will perform the operations for
  the class on the CRC card
• As the performers play out their roles, the
  system will tend to break down.

Text, page 203
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Creating CRC Cards and the Class Diagram

• Object Identification
• Create CRC Cards
• Examine Common Object Lists
• Role-Play the CRC Cards
• Create the Class Diagram
• Review the Class Diagram
• Incorporate Patterns
• Review the Model

• Transfer from the CRC cards the responsibilities
  as operations, and the attributes as attributes,
  and draw the relationships as generalization,
  aggregation, or association
• Add the visibility of the attributes and
  operations
• Examine the model for additional opportunities
  to use aggregation or generalization relationships

Text, pages 203-204
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Creating CRC Cards and the Class Diagram

• Object Identification
• Create CRC Cards
• Examine Common Object Lists
• Role-Play the CRC Cards
• Create the Class Diagram
• Review the Class Diagram
• Incorporate Patterns
• Review the Model

• Review the class diagram for missing and/or
  unnecessary classes, attributes, operations, and
  relationships
• Some analysts normalize the class diagram

Text, page 204
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Creating CRC Cards and the Class Diagram

• Object Identification
• Create CRC Cards
• Examine Common Object Lists
• Role-Play the CRC Cards
• Create the Class Diagram
• Review the Class Diagram
• Incorporate Patterns
• Review the Model

• Use Figure 7-7 to see if a pattern applies

Text, page 204
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Creating CRC Cards and the Class Diagram

• Object Identification
• Create CRC Cards
• Examine Common Object Lists
• Role-Play the CRC Cards
• Create the Class Diagram
• Review the Class Diagram
• Incorporate Patterns
• Review the Model

• A walk-through a formal presentation to another
  group of analysts to go over the CRC cards and
  the Class Diagram

Text, page 204
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Creating CRC Cards and the Class Diagram

• Object Identification
• Create CRC Cards
• Examine Common Object Lists
• Role-Play the CRC Cards
• Create the Class Diagram
• Review the Class Diagram
• Incorporate Patterns
• Review the Model

In each of these steps be sure to record new
information on the CRC cards as it is discovered.
This may require creating new CRC cards and
modifying the Class Diagram.
Text, page 204
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Deliverable V Body

• Structural Modeling (Ch 7) (40 points)
• Class Diagram (30 points)
• CRC cards (10 points)
• Behavioral Modeling (Ch 8) (30 points)
• Sequence Diagrams (10 points)
• Collaboration Diagrams (10 points)
• Statechart Diagrams (10 points)
• Workflow Diagrams (20 points extra credit)