(6,7,8) Software Construction Quiz 3

Slides 6,7, 8

CRC Cards

Contains information of class, responsibility (knows or does), potential collaborators (other class used to get information or perform action)

May contain superclasses/subclasses, description and attributes on back.

Advantages of CRC Cards

Portable, Anthropomorphic, involvement increase, useful, serves as input/starting point, eases transition from process to objects, general size bound

CRC Process

Exploratory phase - find classes, determine responsibilities, collaborators

Analysis phase - collect into subsystems (group classes)

Properties of good class

Clear/recognizable name, uppercase letter singular noun, has responsibilities, participates in system

Class Responsibilities

Public services provided to other objects and system

Knowledge and Action

Knowing - private encapsulated data, related objects, things derived

Doing - creating an object, initiating/controlling action/activities in other objects

Identifying Responsibilities

Verb-phrase identification - identify verbs

Scenarios and role play - walk-through where people play classes

Class enumeration - create initial set of responsibilities and designate them to enumerated classes

Class relationship examination - examine how class relationships fulfill responsibilities

Collaboration

Request from one object to another in order to fulfill a responsibility.

“Is-part-of” Relationship between classes

Imply responsibilities for maintaining information OR fulfill responsibilities by delegating them. (Composition and Aggregation) (students as part of school)

“Has-knowledge-of” Relationship

May know other classes that are not in part-of relationships (associations in UML) (teacher has knowledge of subject)

Collaboration Graph

Arrows point from client(class) to contract(semi-circle).

Exploratory Phase

Identify preliminary list of classes, responsibilities, collaborations. (all identified classes are probably concrete and few may have been identified as abstract)

Analysis Phase

Obtain global understanding of design using Hierarchy graphs, Venn diagrams, Contracts

Hierarchy Graph

Tree representation of inheritance, parents are superclasses, children are subclasses, arcs represent abstract class.

Venn Diagram

Views class as set of responsibilities. (Ordered and Indexable are properties of all Matrix,Array, and String)

If B supports only a part of the responsibilities for A, make a new abstract class C and have both A and B extend from them.

It only takes one responsibility to create an abstract class.

Ellipse and Rectangle are both Filled, so Filled Element is created as an abstract class.

Contract

Set of cohesive responsibilities that a client can depend on. (Defines set of requests client make to server, server is guaranteed to respond). An abstraction analysis technique for refining hierarchy and identifying subsystems.

True Or False: Responsibilities are the basis for determining contracts.

True

True or False: A class can support any number of contracts.

True

True or False: All responsibilites will be part of contract.

False (private responsibilities)

True or False: A responsibility may only be a part of at most one contract.

True (cannot have same responsibility in different contracts)

True or False: Contracts are used in a collaboration

True

Contract Documentation

A contract is a set of responsibilities.

Guideline 1 for Defining Contract

Group responsibilities used by same clients

Guideline 2 for Defining Contract

Maximize cohesiveness of classes

Guideline 3 for Defining Contract

Minimize coupling of classes by reducing the number of contracts

(provide general interface, use polymorphism, look for similar responsibilities to generalize, define classes for classes at the top of hierarchy, add new contracts only for subclasses that add new functionality.