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  1. OMG Issue

OCL25 — OCL 2.1 Inadequate definition of run-time meta-model

  • Key: OCL25-95
  • Legacy Issue Number: 14861
  • Status: open  
  • Source: Model Driven Solutions ( Ed Willink)
  • Summary:

    OCL 2.1 currently specifies an informal run-time meta-model in which all types conform to OclAny. Contributions to this meta-model come from

    • the user meta-model(s)
    • the standard library and its extensions
    • additional constraints

    Problem 1: An OCL AST for an OperationCallExp has a referredOperation that must be able to reference an operation that may come from any of these sources. Issue 12854 raised the problem of referencing additional operations and attributes.

    Problem 2: The almost trivial problem of referencing standard library features has not been raised. If an AST is to be portable between one OCL tool and another there must be a standard URI by which for instance OclAny::= is referenced. Where is this URI specified?

    Problem 3: The semantics of ambiguity resolution between alternative contributions is unclear. UML appears to leave overloading as a semantic variation point, so UML compliance is not helpful. Issue 14591 suggested that a first phase execution created at least a composite UML meta-model.

    Problem 4: OCL 2.1 made clear that there is no reflection at run-time, and introduced OclAny::oclType to compensate. This provides very limited capabilities, in particular there is no counterpart to Element::container().

    A formal run-time model and meta-model can solve these problems. The run-time model is the OCL library model, it's meta-meta-model is the OCL library meta-model and it's meta-meta-meta-model is MOF/UML. NB The OCL library meta-model is not the OCL meta-model.

    The OCL library model comprises primarily oclstdlib::Classifier instances, one of which is named OclAny. OclAny::oclType() returns its oclstdlib::Classifier (NB not a uml::Classifier).

    The oclstdlib::Classifier::conformsTo property (like but not uml::Classifier::general) contributes to the reified type conformance hierarchy.
    The oclstdlib::Classifier::operations property (like but not uml::Classifier::operations) unifies the three sources of available operations, and three different derivations of oclstdlib::Operation accommodate the three types of contribution.

    The oclstdlib model therefore integrates the user's UML meta-model with the standard library and additional constraints and is built during the first phase of execution. The oclstdlib meta-model is much simpler than MOF; there is no need for Associations and ConformsTo is the only Relationship. The semantics of the oclstdlib model defined independently of UML ensure a clear definition of the meaning of OCL execution.

    The oclstdlib model should make no pretence at being UML because it is fundamentally different. One form of oclstdlib::Operation integrates a reference to a uml::Operation into a uniform behavioural structure. oclstdlib::Classifier ::conformsTo provides the modification of the user meta-model to insert OclAny as the bottom type, without modifying the user meta-model.

    With an oclstdlib metaModel, OclAny could provide reflective capabilities such as oclContainer(), oclContents(), oclGet(), oclSet() etc that provide useful reflective capabilities. self.oclType().operations can satisfactorily return a collection of operations even though the operations come from three diverse sources. self.oclType()->closure(conformsTo) will return the type conformance ancestry.

  • Reported: OCL 2.1 — Mon, 14 Dec 2009 05:00 GMT
  • Updated: Thu, 8 Oct 2015 14:12 GMT