The Cascading Bridge Design Pattern

Short Description
The Bridge design pattern [Gamma+95] describes the benefits of decoupling an … This situation can be described by the Cascading Bridge design pattern. …

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Content
The Cascading Bridge Design Pattern
Brendan McCarthy
Sun Java Center
brendan.mccarthy@sun.com
Intent
Separate implementation dimensions into independent classes so they can be varied and evolved
independently. The benefits of this approach apply in designing within sub-systems as well as
architecting across sub-systems. There are some particularly unique benefits for the latter.
Motivation
The Bridge design pattern [Gamma+95] describes the benefits of decoupling an abstraction from
its implementation. In a broader context, there are a number of situations in which it is useful to
treat the “implementation” as multiple independent components (implementation dimensions) to
which additional decoupling benefits apply. For example, the implementation of a query processing
component might consist of an optimizer and an evaluator. While the abstraction of the query
processing component remains constant, either or both of the optimizer or evaluator might be
swapped out for reasons such as:
?The component is broken or does not perform sufficiently well and must be replaced
?A newer and better implementation becomes available, perhaps from a 3rd-party source
?Parallel development teams are incrementally and independently upgrading each component
?Competing implementations must be tested for comparative robustness or…