Annex B: Design Patterns
B3. Chain of Responsibility
Description
When several objects are likely to be able to treat a request according to the context, this pattern allows to avoid the direct coupling between the sender of the request and its processing by one of the potential receivers. A chain of receiving objects then is made up and traversed until one of them handles the request.
Structure and Components
Structure and Components of the Chain of Responsibility design pattern
- Handler defines the interface of a receiver of requests,
- Handler1 and Handler2 concretely treat a request or pass it to their successor,
- ChainClient sends a request.
Collaborations
The request sent by the client is transmitted along the chain until its effective processing.
Collabotations of the Chain of Responsibility design pattern
Strengths and Weaknesses
reduction of the coupling between the client and the
processing of a request by a set of objects which do
not know in advance which effectivelly will be handling
the request,
possibility of dynamically modifying the way of
handling a request,
flexibility in the allocation of the responsibilities
for handling in the objects of processing,
following to the constraints of design, the processing
can not be guaranteed.
Use in CBR*Tools
A design of retain uses this pattern to make the decision of the addition of a case and its indexing into the memory. A chain of decision-makers is then formed, in which each element prepares according to a criterion the response to this request.
Brigitte Trousse
Last modified: Fri Sep 28 13:51:31 MEST 2001