Developing a DSL Graphical Notation - Eclipse Modeling Project: A Domain-Specific Language Toolkit - page 200

Regarding Target End Constraint and Source End Constraint ele-
ments, it's important to realize that these constraints are evaluated based on
mouse position during the act of creating the link. For example, the source end
constraint is evaluated when starting the link, so the context is that element.
The oppositeEnd variable isn't known yet, so don't reference oppositeEnd in
a source end constraint. Likewise, the target end constraint is evaluated
when the mouse hovers over a target element when drawing the link. At this
point, the oppositeEnd environment variable has a value.
Our final mapping is for the generalization link, shown in Table 4.43. Recall
that we'll be using the provided Connection from the classDiagram.
gmfgraph model. Normally, we'd have to load this model using the Load
Resource action, as done before in the graphical definition model. But because
that model includes a reference to the classDiagram.gmfgraph model and is
open in our mapping model resource set, the connection is already available to
our mapping model.

Table 4-43 Generalization Mapping

Element Property Value

Mapping

Link Mapping Containment Feature Class.superclasses : Class

Diagram Link Connection

SolidConnectionWDstClosedArrow

Tool Creation Tool Generalization

Link Constraints

Source End Constraint Body self.superclasses->isEmpty()

Language ocl

Target End Constraint Body *

Language ocl

* As was the case with the Aggregation constraint, this is the verbose OCL constraint for
generalizations:

oppositeEnd <> self and not superclasses->includes(oppositeEnd) and
((oppositeEnd.oclIsTypeOf(dnc::Role) and self.oclIsTypeOf(dnc::Role))
or
(oppositeEnd.oclIsTypeOf(dnc::Party) and self.oclIsTypeOf(dnc::Party))
or
(oppositeEnd.oclIsTypeOf(dnc::Place) and self.oclIsTypeOf(dnc::Place))