CIS 320-07 1

CRC Cards

Class, Responsibility, Collaboration

CIS 320-07 2

CRC Cards

Class, Responsibility, Collaboration CardsOriginally used to teach OOD

Beck and Cunningham (1989) c2.com/doc/oopsla89/paper.html

Not part of UMLUsed in XP (see links on Web site)Integral part of much OOD

CIS 320-07 3

What are they used for?

Identify and clarify objectsUnderstand behaviours for objects and

what they must carry outUnderstand how object cooperate with

one anotherCreating an OO Design

CIS 320-07 4

What is a CRC card?

4x6 card card (or physical substitute)

Class Name

Collaborations (bullet list)

Responsibilities(bullet list)

CIS 320-07 5

CRC Card Advantages

SimpleCheapFamiliarTouchable (manipulate)Shareable (used in a group)Portable (low tech)Possible documentation

CIS 320-07 6

Process

Walk through scenarios Define Classes Add responsibilities Find collaborators

Iterate Use other scenarios

CIS 320-07 7

Defining Classes

Drive using scenarios Start with domain objects and nounsBlue Sky (brainstorm and then refine)What objects are needed to make things

work?

CIS 320-07 8

Defining Responsibilities

Behaviour for which an object is accountable

What work has to be done?Use active verbsUse Cases will suggest responsibilitiesSplit object if too many responsibilities

CIS 320-07 9

Collaborations

Other object which collaborate to create some “higher” behaviour

Physical manipulation of cards during scenario

Overlapping cardsPiling cards (most abstract on top)

CIS 320-07 10

Iterate

Try other scenariosAdd cards as neededAdd responsibilitiesDivide objects if too complexDiscard cards if not used

CIS 320-07 11

Disadvantages

Can be noisy at first Not much quiet time