1. CRC Cards - Tutorial Jun & Azene

2. OBJECTIVES After completing this tutorial, you shall be able to
Know what CRC card is and its history
Know a CRC card session and run
Use CRC for analysis and design of a real object-oriented application
Know CASE tools for CRC cards
Know its strengths and limitations

3. OUTLINE Introduction:OO Concepts and Vocabulary CRC: Overview
CRC Cards for Analysis
CRC Cards for Design
Documenting a CRC Card Design
CASE Tools for CRC Card Design
Exercise: ATM Simulation using CRC
Discussions on the results of the exercise

4. INTRODUCTION OO CONCEPTS AND VOCABULARY

5. INTRODUCTION
“Object-oriented programming offers a new and powerful model for writing computer software. This approach speeds the development of new programs, and, if properly used, improves the maintenance, reusability, and modifiability of software. O-O programming requires a major shift in thinking by programmers, however. The C++ language offers an easier transition via C, but it still requires an O-O design approach in order to make proper use of this technology. … .”
Source:

6. OO Concepts and Vocabulary
OO v/s Non-OO
Non-Object-Oriented (Traditional)
Data and Procedures are kept Separate
Procedures work on Data to produce results
Object-oriented
Focus on Responsibilities - to be satisfied by Objects
Responsibilities translate into Data and Functions within an Object
Objects have behavior
Procedures
Data
SIMILARITIES AND DIFFERENCES
Procedures
Data
Source: Dr. Seaman’s Lecture Note

7. OO Concepts and Vocabulary(Cont
OO Concepts and Vocabulary(Cont.) Phases of OO Systems Development Cycle
Implementation
programming
database access
System Design
system architecture
database access
data structure
algorithms
controls
Object Design
Analysis
application
what
Source: Jeffrey(1999). Advanced System Analysis and Design

8. OO Concepts and Vocabulary (Cont.)
Objects:State,Behavior,Identity
Object-Oriented Model
Encapsulation
Instantiation:Classes and Objects
Inheritance:Classes,Super-classes,and Subclass
Abstract Classes
Polymorphism
Framework and Patterns

9. THE CRC CARD OVERVIEW

10. WHAT’S CRC Card?
CRC stands for Class,Responsibility,and Collaboration.
Class
A set of objects that share common structure and common behavior
Super-class : a class from which another class inherits
Subclass: a class that inherits from one or more classes
Responsibility
Some behavior for which an object is held accountable.
Collaboration
process whereby several objects cooperate to provide some higher-level behavior.

11. WHAT’S CRC CARD? (Cont.)
An index card that is annotated in a group setting to represent a class of objects,its behavior,and its interactions.
An informal approach to OO modeling
Created through scenarios,based on the system requirements,that model the behavior of the system.

12. WHAT’S CRC MODELING CRC Modeling is used:
to develop an OO system more easily 
to teach people about objects and their relationships without teaching them an entire programming language (or even mention programming)
CRC is implemented using the requirements given to a team
Each class is written down on a 3x5 (4x6) inch index card

13. Sample CRC Card (Front & Back)

14. REQUIREMENTS Cards should be physical cards, not virtual cards.
CASE tools for support of CRC cards are useful,but cannot replace the interaction that physical cards facilitate.
3x5 or 4x6 inch are the perfect size. But you can really use anything you want. ….Napkins???Denny’s???
Refreshment (Optional)

15. HISTORY
Introduced at OOPSLA in 1989 by Kent Beck and Ward Cunningham as an approach for teaching object-oriented design.
In 1995,CRC cards are used extensively in teaching and exploring early design ideas.
CRC cards have become increasingly popular in recent years. As formal methods proliferate, CRC cards have become, for some projects,the simple low-risk alternative for doing object-oriented development.

16. THE CRC CARD SESSION
The session includes a physical simulation of the system and execution of scenarios.
Principles of successful session
All ideas are potential good ideas
Flexibility
Group Dynamic
Principles (Similar to the JAD Session)

17. BEFORE THE SESSION Forming the Group
The ideal size for the CRC card team:
5 or 6 people
The team should be composed of
One or two domain experts
two analysts
an experienced OO designer
one group’s leader/facilitator
Roles of the participants and the rule of the game

18. The CRC Card Team Source:The CRC Card Book by Bellin et.al (1997)
Forewords by Kent Beck & Ward Cunningham
Source:The CRC Card Book by Bellin et.al (1997)

19. DURING THE SESSION
All the group members are responsible for holding,moving and annotating one or more cards as message fly around the system.
Group members create,supplement,stack,and wave cards during the walk-through of scenarios.
A session scriber writes the scenarios.

20. PROCESS 1.Brainstorming (Productive thinking)
One useful tool is to find all of the nouns and verbs in the problem statement.
2. Classes Identification
The list of classes will grow and then shrink as the group filters out the good ones.
3. Scenario execution(Role play)
The heart of the CRC card session
With CRC cards,a group of people throw together their ideas about what a system should do,compare them,and synthesize them into a set of classes recorded on CRC cards.
HOW? mean? Where to Start? When to stop? What to Identify? What Scenario is?What Role Plays

21. STRENGTHS The cards and the exercise are non-threatening & informal
Provide a good environment for working and learning.
Inexpensive,portable,flexible,and readily available
Allow the participants to experience first hand how the system will work
Useful tool for teaching people the object-oriented paradigm

22. LIMITATIONS Provide only limited help in the aspects of design.
Do not have enough notational power to document all the necessary components of a system.
Do not specify implementation specifics.
Can not provide view of the states through which objects transition during their life cycle.

23. CRC GOOD PRACTICE Start with the simplest scenarios.
Take the time to select meaningful class names.
Take the time to write a description of the class.
If in doubt,act it out!
Layout the cards on the table to get an intuitive feel for system structure.
Be prepared to be flexible.

24. Analysis techniques to OO development focus on discovering:
CRC CARDS FOR ANALYSIS
Overview
Analysis techniques to OO development focus on discovering:
problem and application domains’ objects and classes
relationships that exist between these objects & classes
way that objects undergo state changes and/or interact with each other over time

25. CRC for Analysis CRC Elements in Analysis: Analysis classes:
classes, scenarios, responsibilities & collaborators
Use the CRC Card sessions to elicit analysis classes, responsibilities and collaborations
Analysis classes:
are classes those describe what the system does
reflect concepts and entities that are part of the domain of being modeled
objects of these classes collaborate to describe what the application does
To create an OO model of an application

26. Case Example: A small technical library system for an R&D organization
Requirement Statement
The CRC Card Sessions
Participants (Who? Why?)
Brainstorming (Scope)
Creating Classes (the first step)
Brainstorming
Suggesting Classes (your suggestions)
Filtering

27. Case example: Finding Classes
Suggested Classes
Library, Librarian, User, Borrower, Article, Material, Item, Due Date, Fine, Lendable, Book, Video, and Journal
Classes after filtering
Librarian, Lendable, Book, Video, Journal, Date, Borrower and User
Assigning Cards
A CRC Card per Class, put name & description of the class

28. Scenarios executions/Role Plays (For what?)
Filter & test identified classes
Identify additional classes
Identify Responsibilities and collaborators
can be derived from the requirements/use cases
responsibilities that are "obvious" from the name of the class (Cautious, avoid extraneous responsibilities)
Filtering and testing R & C
Attributes
(Only important ones are noted)

29. Finding Responsibilities
Are things that the class has knowledge about itself, or things that the class can do with the knowledge it has
Tips/Indicators
Verb extractions in the problem or use case
Ask what the class knows? What/how the class does ?
Ask what information must be stored about the class to make it unique?

30. Finding Collaborators
A class ask another class when
needs information that it does not have or
needs to modify information that it does not have
Client (Requester for services) - Server (Services Provider) relationship
Tips/Indicators
Ask what the class does not knows and need to know? And who can provide that?

31. Case example: Scenarios Execution(cont.)
Identify Scenarios (By domain experts)
Main Categories: check-out, return and search
CHECK-OUT SCENARIO
Who should have the overall responsibilities for the task/check out? Librarian.
What does the task/checking out a book entails?
Refer to the Script to follow the process (handed to students)

32. Case example: Scenarios Execution(cont.)
Major Questions
Shouldn't there be collaborations in the opposite direction?
Collaborations in CRC cards are one-way relationships from the client to the server (OO)
Who should do the checking out of the Book? Librarian or Book itself? (Controversial)
Who should tell Borrower to update its knowledge about outstanding Book? Librarian or Book?

33. Case example: Scenarios Execution(cont.)
Do we need a collaboration between Book and Borrower for the know set of books responsibility?
Collaborations are not usually needed for responsibilities that simply hold information. Instead, Collaboration is needed only for situations where an object actually sends a message to a Collaborator.
Borrower does not need Book's help to put a Book in a set.

34. CRC Cards after the first scenario run

35. Case example: Scenarios Execution(cont.)
Remarks:
Domain experts have a lot contribution
The first scenario takes the longest to walk-through and set the framework
Related scenarios
Superclass discovery
Return scenarios
Exceptional scenarios

36. Case example: Scenarios Execution(cont.)
Search Scenario
"What happens when Ned comes to Library in search of a book entitled The Mythical Mammoth?"
Discovery of new class: Collection class (Why?)
Book can’t look for itself, identity of the book is not know
Collection looks over a set Books to find the correct
Attributes for searching (can be done at Design stage)
When to end scenario execution?
Get a stable model (does not cause new C or R to be added)

37. Grouping Cards
· CRC cards on the table provides a visual representation of the emerging model
· Classes with hierarchical (is-a relationship)
· Class who collaborate heavily placed closer
· Class included by other class (has-a relationship); e.g. Date in Lendable
· Card clustering based on heavy usage or collaborations can provide visual clues to subsystems

38. Deliverables Documenting a CRC Card Analysis
Complete list of Library Application CRC Cards
List of scenarios recorded as suggested and executed
Collaboration Diagram
Application Problem Model

39. Strength & Limitation for Analysis
Common Project Vocabulary
Spreading Domain Knowledge
Making the Paradigm Shift (Role play)
“Every participant is an object, everything happens does so because an object makes it happen” (Wilkinson 1995)
Live Prototyping
to show what the system suppose to do to customers, new member, testers, developers, etc.
Identify Holes in the Requirements
Limitation

40. CRC CARDS for DESGIN Goal of CRC card design process
Expansion and refinement of the Analysis CRC
At level where implementation will be fairly clear
Analysis Classes - describe what the system does. Design Classes - describe how the system works.
1..N Analysis Classes
CRC Card design sessions: Additional classes and mechanisms are built upon the existing analysis classes
0..N Design Classes

41. Design Design classes: are classes those describe how the system does
reflect concepts used by designers and programmers to describe their implementation techniques
include classes that contain the data structures and operations used to implement the analysis as well as classes representing the user interfaces, DBMS, error handlers, etc.
objects of these classes collaborate to describe how the application goals will be accomplished

42. Design Design Constraints Target Environment and Language
Choice of Supporting Software Components: GUI and DBM systems; general and special purpose libraries and frameworks
Class Libraries
Performance Requirements: response-time/ speed, expected availability, load in terms of number of users
Errors/Exceptional Handling
Other: Security, Memory, etc. constraints

43. Applying CRC cards for Design
Elements: CRC, Attributes, scenarios, sub-responsibilities, Lifetime of objects
Classes
Additions that represent mechanisms that support implementation of the problem e.g. Search class
Classes contain the data structures and operations used to implement the analysis classes e.g. Array, List
Interface classes for UI and DBM subsystems
Classes to handle error conditions

44. Applying CRC cards for Design
Scenarios, Responsibilities & Collaborators
take the implementers’ point of view in fulfilling these scenarios, i.e., detailing all system functions (responsibilities), including those that provide support functions (collaborators)
Sub-responsibilities to be added
Collaborating sub-responsibilities to be added
Message Data Passed (can be differed until the low-level design)
The Process:
Problem-modeling scenarios are repeated along with additional new scenarios as needed
High-level responsibilities & collaborators are used, and detailed and expanded

45. Applying CRC cards for Design
The distinction between objects and classes becomes more important, and the following questions, are answered will be an important part of its design.
Who creates this object?
What happens when it is created and adopted?
What is the lifetime of the object vs. the life time of the information (persistence) held by an object?
Attributes
Discovery of attributes that are necessary to support the task during examination of each responsibility
What attributes of objects need to be saved persistently
Leads to a database design (database model)

46. Case: Library Application Design
Group: Who and why?
The two designers (Cecilia and Jim), OO expert (Nancy) as a facilitator, Betty (a domain expert/user)
Input: CRC cards, Scenarios, diagrams, etc. from Analysis stage; Design Constraints
The Session/Process
Brainstorming
Add sub-responsibilities while revising the analysis classes
Add data/object that is passed with the message being sent (can be differed at the end of the design stage as it takes the design to low level)
Figure 5.3. pp. 116

47. Case: Library Application Design
Brainstorming any classes that comes to mind based on design constraints such as
User Interface, Database access, Mechanisms for implementation of analysis classes, error handlings
User Interact class & DB interface Classes
Scenarios identification and executions
Object creation scenarios
Check-out Scenario
Return Scenario
Search Scenario
Output: Design classes

48. Case: Library Application Design
Classes that serves as interfaces to other subsystems (UI and DBMS)
Principles:
make independent of specific hardware and software products
use specific class names instead of generic names such as GUI and DBMS
User interface: to get input from and display to user using GUI software classes
UI manager, User Interacter classes are suggested.

49. Case: Library Application Design
Database: To obtain and store Borrower objects and objects of the Lendable classes using DBMS software
Scenario Executions (Scripts given)
Creation Scenarios (System start-up)
Check-out scenario
Others

50. Case: Library Application Design
some important issues during Scenarios execution
How to verify the ID? Who? Librarian? A new class?
How the Lendables set are stored and manipulated? Data Structure issues? List is chosen
Scenarios, Scenarios, Scenarios
Work on normal and exceptional (Error handling class)
When to start Prototyping?

51. Deliverables Documenting a CRC Card Design
List of design classes (pp )
Class models: Hierarchies and collaboration graphs (pp )
Scenario Descriptions (pp )

52. Strength & Limitation for Design
Common project vocabulary
Spread of domain knowledge
Spreading OO design expertise
Design Reviews
Frame for implementation
Informal notation
“Designing is not the act of drawing a diagram” (Booch)
Limitations

53. CASE tools for CRC Card An automated tool to support CRC cards
Quick CRC from Excel Software
From SpiralSoft
Rational & others Modeling Methods and CASE Tools.
Features

54. Class Exercise
Case: Simulation of AMT

55. References
Wilkinson, N. C. (1995). Using CRC cards: An informal approach to object-oriented development. SIGS Book, USA
Bellin, D. and Simone, S. S The CRC Card Book. Addison Wesley Longman, Inc.: USA.
Beck, Kent, and Ward Cunningham. " A Laboratory for Teaching Object-Oriented Thinking." OOPSLA-89 Proceedings, SIGPLAN Notices 24 (10): 1-6 (October 1989). URL:
Jeffrey, H. and et al. (1999). Modern systems analysis and design. Reading, Mass: Addison-Wesely.
Bjork, R. C ATM Simulation Links - by Topic.
Techniques for Object Oriented Analysis and Design.
Object-Oriented Design Using CRC Cards.
Malan, R., et al. (1995). Lessons from the Experiences of Leading-Edge Object Technology Projects in Hewlett-Packard. OOPSLA'95 Conference Proceedings, Austin, Texas.
Hutt, A.(1994). Object Analysis and Design: Description of Methods. JohnWilley & Sons, Inc., New York.
Fowler, Martin. (1997). A survey of object oriented analysis and design methods.

56. Reference (Cont.)
A tool for designing Java programs with UML . Proceedings of the 4th annual SIGCSE/SIGCUE on Innovation and technology in computer science education, June , 1999, Krakow Poland
Object-oriented practice in 1998 (panel): does it help or hinder collaboration? Pages
CRC CARD CONSTRUCTOR.
Techniques for Object Oriented Analysis and Design.
Cockburn, A. (March 1999) Using CRC Cards [Online]. [03/29/2001].
SpiralSoft Home Page.
Object-Oriented Design Using CRC Cards.
Object-Oriented Analysis Phase
Modeling Methods and CASE Tools.