The use of DSMLs is often limited by a lacking possibility to define domain-specific association types. This is an obstacle to reusing domain-specific knowledge and also a threat to model Integrity, since modelers are not prevented from creating inappropriate associations.
Recently, the XModelerML has been extended by a feature that allows for the convenient definition of assocication types. There is a new screencast that illustrates the definition and use of association types with the XModelerML.