The Henshin Trace model is an EMF model which provides generic and flexible traceability support for exogenous model transformations in Henshin. Exogenous transformation are used to translate one or more source models into one or more target models. The trace model is used to keep track of the translated elements during the transformation. This is necessary because in general source and target models need to be related in any way.
The trace model consists of a single class Trace which has two non-containment n-ary references called source and target. These two references are of type EObject and therefore can be used to refer to any EMF object. This is also the reason why we say that the trace model is generic. In addition to the source and target references, traces can be named and can contain subtraces.
Importing the Trace Model
To use the trace model in an exogenous transformation, all you need to do is to import the trace package into your transformation and to use it in the transformation rules. To import the trace model, use the context menu entry Import Packages... -> From Registry in one of the Henshin editors and choose this URI: http://www.eclipse.org/emf/2011/Henshin/Trace.
Using the Trace Model
Suppose you want to translate EClasses to GenClasses and all their EAttributes to GenFeatures. Then you could use the following to transformation rules:
Here, the trace element between EClass and GenClass is used to find out in which GenClass the new GenFeature should be contained in.
Remark: for the above translation the Trace model is actually not needed because the elements in GenModel keep references to the Ecore elements themselves. In general, the source and target models in exogenous transformations may not be related and therefore the Trace model is necessary.