Design Patterns Explained

Chapter 12 • Solving the CAD/CAM Problem with Patterns 2O5
Thus, the Bridge pattern creates the context for the Adapter pattern.
I can eliminate the Adapter pattern as a candidate for senior-most
pattern.
The relationship between context and used by.
Often, it seems that when one pattern uses another pattern, the
pattern that is used is within the context of the pattern doing the
using. There are likely exceptions to this rule, but it seems to
hold most of the time.
Now I only have to compare Bridge-Facade and Facade-Adapter.
I will look at the Bridge and Facade relationship first because if the
Bridge turns out to be the primary pattern there as well, I do not
need to consider the Adapter-Facade relationship (remember, I am
only trying to identify the seniormost pattern at this point).
It should be readily apparent that the same logic that applied to
Bridge and Adapter also applies to Bridge and Facade:
• I will be using the Facade pattern to simplify the V1 system's
interface.
• But what will be using the new interface I create? One of the
implementations of the Bridge pattern.
Therefore, the Bridge pattern creates the context for the Facade.
The Bridge is the seniormost pattern.
According to Alexander, I am supposed to start with the whole.
Going back to the beginning, I find that I do not yet have the context
for the Bridge.
One down, two to go
The Bridge-Facade
relationship
The Bridge is the
winner