I've said it before and I'll say it again.  I hate UML.  That doesn't mean there aren't pictures that can say 1000 words.  Here's approximately 6000 words on the subject of substitution patterns.  Substitution patterns are patterns where you want functionality to expose a certain interface, but need some sort of bridging logic to achieve that. One nice thing about all of these patterns is that they describe an object.  Patterns that involve several actors are harder to name and explain.  Here, you've got the object that implements the pattern, and the target.  The target never knows anything about...