Editing Meta-Object Facility (section)

== Metamodeling architecture ==
MOF is a ''closed'' metamodeling architecture; it defines an M3-model, which conforms to itself. MOF allows a ''strict'' meta-modeling architecture; every model element on every layer is strictly in correspondence with a model element of the layer above. MOF only provides a means to define the structure, or [[abstract syntax]] of a language or of data. For defining metamodels, MOF plays exactly the role that [[EBNF]] plays for defining programming language grammars. MOF is a [[Domain Specific Language]] (DSL) used to define metamodels, just as EBNF is a DSL for defining grammars. Similarly to EBNF, MOF could be defined in MOF.

In short, MOF uses the notion of '''MOF::Classes''' (not to be confused with '''UML::Classes'''), as known from [[Object-oriented programming|object orientation]], to define concepts (model elements) on a metalayer. MOF may be used to define object-oriented metamodels (as [[Unified Modeling Language|UML]] for example) as well as non object-oriented metamodels (e.g. a [[Petri net]] or a [[Web Service]] metamodel). 

As of May 2006, the [[Object Management Group|OMG]] has defined two compliance points for MOF:
*EMOF for Essential MOF<ref name=mof241>{{cite web|title=OMG Meta-Object Facility (MOF) Core Specification, Version 2.4.1|url=http://www.omg.org/spec/MOF/2.4.1/PDF|publisher=[[Object Management Group]]|access-date=17 February 2014|page=1}}</ref> 
*CMOF for Complete MOF<ref name=mof241/>

In June 2006, a ''request for proposal'' was issued by OMG for a third variant, SMOF (Semantic MOF).

The variant '''ECore''' that has been defined in the '''[[Eclipse Modeling Framework]]''' is more or less aligned on OMG's EMOF. 

Another related standard is [[Object Constraint Language|OCL]], which describes a formal language that can be used to define model constraints in terms of [[predicate logic]].

[[QVT]], which introduces means to query, view and transform MOF-based models, is a very important standard, approved in 2008.  See [[Model Transformation Language]] for further information.