MDA Distilled: Principles of Model-Driven Architecture

Marking Models

A mapping rule that, for example, turns a UML attribute into transient data on the heap may not always be appropriate. In some cases, there may also be a need for persistent attributes, so we need to have two mapping rules and additional mapping inputs that select which rule to apply. These additional mapping inputs take the form of marks, which are lightweight, nonintrusive extensions to models that capture information required for model transformation without polluting those models.

A mapping may use several different marks associated with the source models; conversely, a mark may cater to several different mappings. There also may be global marks that aren't necessarily related to individual model elements. However, marks mustn't ...