Responsibility-Driven Design

• Responsibility implies Non-Interference
• Works better for programming-in-the-large vs. programming-in-the-small
  • Where software is built by team and responsibility must be shared
  • Where the management of details and COMMUNICATION are the main problems

Tasks in RDD

• Work through scenarios
• Identify components
  • Components have a small well-defined set of responsibilities
  • Components should interact with other components to the minimal extent possible
• CRC Cards-Recording Responsibility

Component, Responsibility, Collaborator (CRC) Cards

Why CRC Cards?

• Give Components a Physical Representation
• The What/Who Cycle
• Documentation

Components and Behavior

• Postpone Decisions
• Prepare for Change
  • Primary objective: Changes should affect as few components as possible
  • Try to predict likely sources of change and isolate those
  • Try to isolate and reduce hardware dependencies
  • Reduce coupling
  • Record major decisions

Interaction Diagrams

• Replacement for "I am..." notation

Coupling and Cohesion

• Cohesion is the degree to which the responsibilities of a single component form a meaningful unit
• Coupling describes the relationship between software components
• Goal: Reduce coupling, increase cohesion

Parnas' Principles: Interface and Implementation

• Separate them

The developer of a software component must provide the intended user with all the information needed to make effective use of the services provided by the component, and should provide no other information

The developer of a software component must be provided with all the information necessary to carry out the given responsibilities assigned to the component, and should be provided with no other information