OCLps is a subset of OCL. No side effects, and you cannot use your methods even if they are marked with IsQuery. The collect, groupby and other operators that return tuples are not supported. The reason is that the main use of OCLps is to return a list of identities based some criteria’s from select or difference or the like. Once MDriven has the set of identities we will load the corresponding objects – then you can take over with normal OCL.