What is MDT OCL?
MDT OCL provides a parser and interpreter for OCL constraints and expressions on any EMF-based metamodel. By that is meant any metamodel whose meta-metamodel is Ecore, and which (in being a metamodel) provides an EMF importer to create GenModels that generate a Java implementation.
So far, the Eclipse Modeling Project has two such metamodels: Ecore and UML (Ecore being its own meta-metamodel). Hence, the OCL component provides an OCL binding for each of these metamodels. OCL can parse constraints in either Ecore or UML models, and can evaluate them on the instances of Java classes generated from these models.
In terms of the OMG's modeling "stack", then, we have in the Eclipse Modeling Project
|Modeling Level||Artifacts||OCL's Role|
|M3||Ecore||This is the metamodel for the OCL Abstract Syntax Model|
|M2||Ecore, UML||OCL's generic AST model binds to these metamodels|
|M1||*.ecore and *.uml models||OCL parses constraints on these models|
|generated Java code|
|M0||instances of generated Java classes||OCL evaluates constraints on these objects|
|dynamic EMF objects|
The OCL Abstract Syntax Model is, itself, actually a metamodel sitting at the M2 level.