GRASP Patterns Overview

What are GRASP Patterns?

They describe fundamental principles of object design and responsibility assignment, expressed as patterns. 
After identifying your requirements and creating a domain model, then add methods to the software classes, and define the messaging between the objects to fulfill the requirements.
The GRASP patterns are a learning aid to help one understand essential object design, and apply design reasoning in a methodical, rational, explainable way. This approach to understanding and using design principles are based on patterns of assigning responsibilities.

Responsibilities and Methods

The UML defines a responsibility as "a contract or obligation of a classifier". Responsibilities are related to the obligations of an object in terms of its behavior. Basically, these responsibilities are of the following two types:
  • knowing
  • doing
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
Responsibilities are assigned to classes of objects during object design. For example, I may declare that "a Sale is responsible for creating SalesLineltems" (a doing), or "a Sale is responsible for knowing its total" (a knowing). Relevant responsibilities related to "knowing" are often inferable from the domain model because of the attributes and associations it illustrates.

 POS (Point Of Sale) application is used to explain all the GRASP Patterns.

Let's understand the POS(Point Of Sale) application briefly and then apply GRASP Patterns to POS Application.

Point of Sale (POS) application

Let's consider Point of Sale (POS) application: a Brief overview of POS application.
  1. Application for a shop, restaurant, etc. that registers sales.
  2. Each sale is of one or more items of one or more product types and happens at a certain date.
  3. A product has a specification including a description, unitary price, and identifier.
  4. The application also registers payments (say, in cash) associated with sales.
  5. A payment is for a certain amount, equal or greater than the total of the sale.

How to Apply the GRASP Patterns (General Responsibility Assignment Software Patterns)
Let's discuss five GRASP patterns. There is a separate Post for each GRASP Pattern

    Comments

    Post a Comment

    Popular posts from this blog

    Design Patterns used in Hibernate Framework

    Image
    In this post, let's discuss a different kind of design patterns which are widely used in the Hibernate Framework. Design Patterns denote the best computer programming practices in the object-oriented software development. Hibernate framework has been built by using the following design pattern or standard practices. I list few known design patterns used in Hibernate Framework. Please mention in a comment, if you know any other design patterns used in Hibernate Framework. You can also read my post of  Design Patterns used in Spring Framework Domain Model Pattern The domain model is treated as POJO in Hibernate. The domain model is an object model of the domain that incorporates both behavior and data. Read more about Domain Model Pattern here https://stackoverflow.com/questions/41335249/domain-model-pattern-example Proxy Design Pattern Proxy Pattern for lazy loading - https://docs.jboss.org/hibernate/orm/3.3/reference/en/html/performance.html Proxy Pattern provides a surrogate ...
    Read more

    Value List Handler

    The  Value List Handler  provides the search and iteration functionality. To perform a search, the Value List Handler uses a  Data Access Object  to execute the query and retrieve the matching results from the database. It is hard to understand this pattern so my suggestion is to go to  source code  section and have a look at code step by step gives you more clarity. This pattern is divided into a number of sections for simplicity like problem, forces, solution etc. Problem (Problem section describes the design issues faced by the developer) You have a remote client that wants to iterate over a large results list. Forces (This section describes Lists the reasons and motivations that affect the problem and the solution. The list of forces highlights the reasons why one might choose to use the pattern and provides a justification for using the pattern) You want to avoid the overhead of using EJB finder methods for large searches. You want to implement a...
    Read more