CSC/ECE 517 Fall 2010/ch7 7b vk
Information Expert Pattern is one of the GRASP patterns or principles, used as a mental aid to help assigning responsibilities to various software classes, in the design of object oriented software.
Introduction
Object oriented design is a process of building a system of interacting objects to solve a given software problem. It can be otherwise defined as, identifying requirements and creating a domain model, then adding methods to the software classes, and defining the messaging between the objects to fulfill the requirements. But, deciding what methods belong where, and how the objects should interact, is critically important in the designing process and is something non-trivial.
Experienced Object-oriented developers build up a repertoire of both general principles and idiomatic solutions that guide them during Object oriented design phase of the software. The principles and idioms, if codified in a structured format describing the problem and solution, and given a name, may be called as patterns.
General Responsibility Assignment Software Patterns (or Principles), popularly known as GRASP, are a set of guidelines for assigning responsibility to software classes and objects in object oriented design. Information Expert Pattern is first among the basic five GRASP Patterns, Information Expert, Creator, High Cohesion, Low Coupling and Controller, which address very basic, common questions and fundamental design issues.
Information Expert Pattern is also known as Expert Pattern.
Responsibilities and Methods
The OMG in its UML standard specification defines a responsibility as "a contract or obligation of a classifier". These responsibilities are of two types.
- doing
- knowing
Doing responsibilities of an object include:
- doing something itself, such as creating an object or doing a calculation
- initiating action in other objects
- controlling and coordinating activities in other objects
Knowing responsibilities of an object include:
- knowing about private encapsulated data
- knowing about related objects
- knowing about things it can derive or calculate