Editing Meta-Object Facility

{{Short description|Standard of Object Management Group}}
[[Image:M0-m3.png|thumb|320px|Illustration of the Meta-Object Facility.]]
The '''Meta-Object Facility''' ('''MOF''') is an [[Object Management Group]] (OMG) standard for [[model-driven engineering]]. Its purpose is to provide a [[type system]] for entities in the [[CORBA]] architecture and a set of interfaces through which those types can be created and manipulated.
MOF may be used for [[Domain-driven design|domain-driven software design]] and [[Object-oriented modeling|object-oriented modelling]].{{r|mof241|page=15}}

== Overview ==
MOF was developed to provide a [[type system]] for use in the [[CORBA]] architecture, a set of schemas by which the structure, meaning and behaviour of objects could be defined, and a set of CORBA interfaces through which these schemas could be created, stored and manipulated.<ref>{{cite web|title=Common Facilities RFP-5: Meta-Object Facility|url=http://www.omg.org/cgi-bin/doc?cf/96-05-02.pdf|publisher=Object Management Group|access-date=14 January 2014|date=2 May 1996}}</ref> 

MOF is designed as a four-layered architecture. It provides a meta-meta model at the top layer, called the M3 layer. This M3-model is the language used by MOF to build metamodels, called M2-models. The most prominent example of a Layer 2 MOF model is the UML metamodel, the model that describes the UML itself. These M2-models describe elements of the M1-layer, and thus M1-models. These would be, for example, models written in UML. The last layer is the M0-layer or data layer. It is used to describe real-world objects.

Beyond the M3-model, MOF describes the means to create and manipulate models and metamodels by defining [[CORBA]] interfaces that describe those operations. Because of the similarities between the MOF M3-model and UML structure models, MOF metamodels are usually modeled as UML class diagrams. 

=== File formats ===
A conversion from MOF specification models (M3-, M2-, or M1-Layer) to W3C XML and XSD are specified by the [[XML Metadata Interchange|XMI]] (ISO/IEC 19503) specification. XMI is an XML-based exchange format for models.{{r|mof241|page=xi}}

From MOF to Java™ there is the Java Metadata Interchange (JMI) specification by [[Java Community Process]].{{r|mof241|page=xi}}

It also provides specs to make easier automatic CORBA IDL interfaces generation.{{r|mof241|page=3}}

== 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.

== International standard ==
MOF is an international standard:
;MOF 2.4.2
:[[International Organization for Standardization|ISO]]/[[International Electrotechnical Commission|IEC]] 19508:2014 Information technology — Object Management Group Meta Object Facility (MOF) Core
;MOF 1.4
:[[International Organization for Standardization|ISO]]/[[International Electrotechnical Commission|IEC]] 19502:2005 Information technology — Meta Object Facility (MOF)

MOF can be viewed as a standard to write [[Metamodeling|metamodels]], for example in order to model the abstract syntax of [[Domain Specific Language]]s. [[Kermeta]] is an extension to MOF allowing executable actions to be attached to EMOF meta-models, hence making it possible to also model a DSL operational semantics and readily obtain an interpreter for it.

[[Java Metadata Interface|JMI]] defines a Java API for manipulating MOF models.

OMG's MOF is not to be confused with the Managed Object Format (MOF) defined by the [[Distributed Management Task Force]] (DMTF) in section 6 of the Common Information Model (CIM) Infrastructure Specification, version 2.5.0.<ref>[http://www.dmtf.org/standards/published_documents/DSP0004_2.5.0.pdf Common Interface Model (CIM) Interface Structure, version 2.5.0]</ref>

== See also ==
{{div col|colwidth=22em}}
* [[Common Warehouse Metamodel]]
* [[Domain-specific language]]
* [[Kermeta]]
* [[KM3]]
* [[Metamodeling]]
* [[Metadata]]
* [[Model-driven architecture]]
* [[OGML]]
* [[Platform-specific model]]
* [[QVT]]
* [[SPEM]]
* [[XML Metadata Interchange]]
{{div col end}}

==References==
{{reflist}}
{{Refimprove|date=February 2009}}

== Further reading ==
*Official MOF specification from OMG
*Ralph Sobek, MOF Specifications Documents
*Johannes Ernst, ''What is metamodeling?''
*Woody Pidcock, ''What are the differences between a vocabulary, a taxonomy, a thesaurus, an ontology, and a meta-model?''
*Anna Gerber and Kerry Raymond, MOF to EMF and Back Again.
*Weaving Executability into Object-Oriented Meta-Languages
*MOF Support for Semantic Structures RFP Request For Proposal on SMOF

== External links ==
{{Commonscat|Meta-Object Facility}}
* [http://www.omg.org/mof/ OMG's MetaObject Facility]
{{ISO standards}}

[[Category:Specification languages]]
[[Category:Data modeling]]
[[Category:Unified Modeling Language]]
[[Category:ISO standards]]