crc cards c lass r esponsibility c ollaborator copyright © 1999 patrick mcdermott uc berkeley...

CRC Cards

Class Responsibility Collaborator

Copyright © 1999 Patrick McDermott

UC BerkeleyExtension

pmcdermott@msn.com

Although not strictly part of the UML, CRC (Class-Responsibility-Collaborator) Cards are often useful for learning requirements from users.

Class• A Thing the Business needs to know about.• At this stage, a business person should be

able to understand every one of them.

• “Class” is best defined by examples…

Examples of Classes• Tangible• Intangible• People• Places• Things• Events• Roles• Organizations• Other Systems

• Collections of Other Objects• Conceptual: Cost Center, Account• Interface: Screen• Infrastructure: Date, Money, Address• Persistence: Database• Control

There Must be a Class if…… There’s a file… There’s a form… There’s a number… There are multiple copies… It’s Important

NOTE—– Sections and boxes on Forms– The name might not be obvious

They’re Everywhere!

Classes have Responsibilities• Personification Helps

– What if a person, not a computer, does it?– Obligation or Contract

• Know Things– Invoice: Know who the Customer is

• Do Things– Invoice: Compute Total

• Get Organized– Abstraction

A Responsibility might usea Collaborator

• Some Relationship between two classes• Another class that assists in fulfilling the

Responsibility– Has information (Knows something)– Helps accomplish the Task– No need to List Both Directions (Reverse is implied)

• A verb should connect the two• A Customer Pays an Invoice• A Student Registers for a Class

• Personification (or messaging) can help– The Pathetic Fallacy is Preferred– Act Like the class is a Person– How was it done B.C.? [Before Computers]

A CRC Card

A Responsibility Collaborator

Another Responsibility Collaborator

A Great Responsibility Collaborator

NAME

Attributes• Attributes are facts about classes• Do not attempt to list all possible attributes• List only attributes that are

– Defining– Likely to be forgotten– Politically Important

• Do not make get/sets for all attributes

A CRC Card Session

1. Prepare the Group• Ice Breaker?• Choose a scribe

2. Brainstorm Class List

3. ACE it: Add, Combine, Eliminate

4. Make Cards

5. Write Descriptions

6. Brainstorm Responsibilities & Collaborators

7. Review

8. Sketch UML Class Diagram with Cards

Brainstorming Rules

0. Have Fun!!!1. No Criticism or Debate2. No Self-Censorship3. Piggyback

Quantitynot

Quality

Steps

1. Brainstorm

2. Reward

3. Reality Check

4. Fuse & Fission

5. Categorize, Cluster & Combine

6. SelectConsensus

Multi-Vote

PurchaseOrder

A Purchase Order (PO) is prepared by a customer and sent to us to order goods or services. The term "Purchase Order" has a special legal meaning under the Uniform Commercial Code (UCC) and implies a huge volume of terms and conditions that are set out in the UCC.

Packing Slip

A PO is technically a legal offer to pay us a certain amount for the goods ordered. We can turn the PO into a contract by accepting the offer. The simplest way to accept an offer is to perform on it, in this case by shipping the goods. We prepare a Packing Slip as a record of the shipment.

Invoice

An Invoice is a demand for payment. The invoice is sometimes legally necessary but also shows the customer the calculation of the total.

Receipt

A Receipt is acknowledgement of payment. Receipts are usually only prepared when the payment is in cash; in other cases the customer’s canceled check serves as the receipt.