CSC/ECE 517 Fall 2010/ch7 7c DF

Pure Fabrication pattern

Introduction

The GRASP design patterns suggest methods in which the responsibilities of a system can be distributed amongst classes. One of these is the pure fabrication principle, which guides the creation of classes that are not directly represented within a system's problem domain. Pure fabrication indicates that such extra classes should be created when there are responsibilities that do not fit well within any objects. By fabricating these extra classes, the designer is able to maintain a higher level of cohesiveness with less coupling than would be the case if the responsibilities were relegated only to the classes directly related to the problem domain.

Role in Doman Driven Design

One of the most common situations in which the pure fabrication principle can be seen is domain driven design. This is a process for system design which focuses on the core model of the problem domain. It results in a hierarchy of abstractions, the highest level of which are aggregate elements. Each aggregation represents a top-level component in the problem domain and is manipulated by a set of services. These services implement responsibilities required by the system; however, they are distrinct from the model aggregations derived from the problem domain. As such, they are implementations of the pure fabrication pattern which are created during the design of the system to maintain high cohesion of the domain's aggregations while minimizing coupling between them.