I think you have to add LinkConstraints element for LinkMapping representing
a link from 'x' to 'x' and SourceEndConstraint into it. This SourceEndConstraint
can be expressed using OCL like:
self.incomingXLinks->size() = 0
In addition to make this constraint working you have to have âincomingXLinksâ
feature pointing to the incoming links into this X instance in your meta-model
and this reference should be set to appropriate âlinkâ on creating âx1â->âx2â
link in the model.