Dharma's Excel VBA > About object-oriented > Object-oriented design and GRASP Pattern
Created August 15, 2010
Last updated August 15, 2010
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Object-oriented design and GRASP Pattern

  In this page , I will introduce 1 the GRASP Pattern 2 that is a pattern about assigning responsibility to classes when we design in object-oriented.

  Before reading this page , if you don't know the module cohesion and module coupling , please read "Object-oriented and the Module Cohesion and the Module Coupling - Dharma's Excel VBA" previously.

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Note.
1. I'm sorry , I don't know the GRASP pattern in detail. Therefore , I can not explain it.
2. The GRASP pattern is a range of UMTP L3.

1. What is the GRASP Pattern ?
2. Reference


1. What is the GRASP Pattern ?

  The GRASP Patten( General Responsibility Assignment Software Patterns ) is a pattern about assigning responsibility to classes when we design in object-oriented.

  The GRASP Pattern has the followings patterns (Table 1).

Table 1 - Patterns in the GRASP Pattern
1. Information Expert
Problem: What is a basic principle by which to assign responsibilities to Objects ?
Solution: Assign a responsibility to the class that has the information needed to fulfill it.
Merit: The informations are encapsulated. The module coupling between classes becomes lower. The informations are dispersed and understandable. And the class that the module cohesion is high is defined.
Related patterns:Low Coupling Pattern , High Cohesion Pattern
2. Creator
Problem: Who should be responsible for creating a new instance of some class ?
Solution: Assign class B the responsibility to create an instance of class A if one of these is true (the more the better):
  • B "contains" or compositely aggregates A.
  • B records A.
  • B closely uses A.
  • B has the initializing data for A that will be passed to A when it is crated. Thus B is an Expert with respect to creating A.

Merit: The module coupling between classes becomes lower.
Related patterns: Low Coupling Pattern
3. Controller
Problem: What first object beyond the UI layer receives and coordinates ("controls") a system operation ?
Solution: Assign the responsibility to a class representing one of the following choices:
  • Major subsystem classes
  • A use case scenario classes within which the system event occurs
Merit: The classes are more reusable. The chance to judge the state of the use case is obtained.
4. Low Coupling
Problem: How to support low dependency, low change impact, and increased reuse ?
Solution: Assign a responsibility so that coupling remains low.
Merit: The class is more independent from the change of the other classes. The class is more understandable. The classes are more reusable.
Related patterns: Protected Variations Pattern
5. High Cohesion
Problem: How to keep objects focused, understandable, and manageable, and as a side effect, support Low Coupling ?
Solution: Assign a responsibility so that cohesion remains high.
Merit: The clearness and understandability of the design is higher. The maintenance and enhancing is easier. The module coupling between classes becomes lower.
6. Polymorphism
Problem: How to design the choices which is dependent by the class ?
Solution: The same name operations (methods) in the difference classes is defined. And assign a responsibility to the class the class that the behavior is changed.
Merit: When the variation ( choice ) increases newly, it is possible to enhance it easily.
Related patterns: Protected Variations Pattern. There are related patterns in Gang of Four Design Patterns.
7. Pure Fabrication
Problem: How to become higher cohesion and lower coupling ? (When it doesn't go well in other pattern )
Solution: Define a class for convenience' sake that doesn't express the concept of the problem area at all.
Merit: The module cohesion of the class is higher. The classes are more reusable.
Related patterns: Low Coupling Pattern , High Cohesion
8. Indirection
Problem: To de-couple objects so that Low coupling is supported and reuse potential remains high?
Solution: Assign the responsibility to an intermediate object to mediate between other components or services, so that they are not directly coupled.
Merit:The module coupling between classes becomes lower.
Related patterns:Protected Variations Pattern , Low Coupling Pattern , Pure Fabrication Pattern. There are related patterns in Gang of Four Design Patterns.
9. Protected Variations
Problem:How can we design objects , subsystems and systems such that the variations in these do not have an undesirable impact on other elements in the system?
Solution: Assign responsibility to create a stable interface around an unstable or predictably variable subsystem or component.
Merit: When the variation increases newly, it is possible to enhance it easily. The module coupling between classes becomes lower.
Related patterns: There are a lot of related pattern in the GoF design patterns.

  If you think the Table 1 is not understood easily ( I'm soryy ) , please read the "2. Reference".
  If you don't know the GRASP Patterns , I think that the practiced one is most 1.   In the GRASP Patterns , the most important patterns are "Low Coupling" and "High Cohesion". If you need the details , please read "Object-oriented and the Module Cohesion and the Module Coupling - Dharma's Excel VBA".
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Note. 1:
  Then, isn't it significant to this? It is No. The thing that the pattern is named, is important. When in reviewing the specifications , coaching subordinates and communicating other person , if name is not existed , we have a hard time.
And , by named, the persuasive power become higher.
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2. Reference

  The following tables are pages that I referred to create this page.


No.

Linked Website Name

Description

Linked date
1 GRASP - Designing Objects with Responsibilites - A Methodical Approach to Basic OO Design This page introduces the GRASP Pattern. August 15, 2010
2 GRASP patterns This page introduces the GRASP Pattern. August 15, 2010
3 GRASP Patterns This page introduces the GRASP Pattern. August 15, 2010
4 GRASP (Object Oriented Design) This page introduces the GRASP Pattern. August 15, 2010

No.

Author

Book Name

ISBN
1 Craig Larman Applying UML and Patterns: An Introduction to Object-Oriented Analysis and Design and Iterative Development (3rd Edition) 978-0131489066


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