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 software design and object-oriented modelling. [1] : 15
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. [2]
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.
A conversion from MOF specification models (M3-, M2-, or M1-Layer) to W3C XML and XSD are specified by the XMI (ISO/IEC 19503) specification. XMI is an XML-based exchange format for models. [1] : xi
From MOF to Java™ there is the Java Metadata Interchange (JMI) specification by Java Community Process. [1] : xi
It also provides specs to make easier automatic CORBA IDL interfaces generation. [1] : 3
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 orientation, to define concepts (model elements) on a metalayer. MOF may be used to define object-oriented metamodels (as 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 OMG has defined two compliance points for MOF:
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 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.
MOF is an international standard:
MOF can be viewed as a standard to write metamodels, for example in order to model the abstract syntax of Domain Specific Languages. 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.
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. [3]
The unified modeling language (UML) is a general-purpose visual modeling language that is intended to provide a standard way to visualize the design of a system.
The XML Metadata Interchange (XMI) is an Object Management Group (OMG) standard for exchanging metadata information via Extensible Markup Language (XML).
A platform-specific model is a model of a software or business system that is linked to a specific technological platform. Platform-specific models are indispensable for the actual implementation of a system.
Model Driven Architecture (MDA) is a software design approach for the development of software systems. It provides a set of guidelines for the structuring of specifications, which are expressed as models. Model Driven Architecture is a kind of domain engineering, and supports model-driven engineering of software systems. It was launched by the Object Management Group (OMG) in 2001.
The Object Constraint Language (OCL) is a declarative language describing rules applying to Unified Modeling Language (UML) models developed at IBM and is now part of the UML standard. Initially, OCL was merely a formal specification language extension for UML. OCL may now be used with any Meta-Object Facility (MOF) Object Management Group (OMG) meta-model, including UML. The Object Constraint Language is a precise text language that provides constraint and object query expressions on any MOF model or meta-model that cannot otherwise be expressed by diagrammatic notation. OCL is a key component of the new OMG standard recommendation for transforming models, the Queries/Views/Transformations (QVT) specification.
Given that metadata is a set of descriptive, structural and administrative data about a group of computer data, Java Metadata Interface is a platform-neutral specification that defines the creation, storage, access, lookup and exchange of metadata in the Java programming language.
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A metamodel is a model of a model, and metamodeling is the process of generating such metamodels. Thus metamodeling or meta-modeling is the analysis, construction and development of the frames, rules, constraints, models and theories applicable and useful for modeling a predefined class of problems. As its name implies, this concept applies the notions of meta- and modeling in software engineering and systems engineering. Metamodels are of many types and have diverse applications.
ATL is a model transformation language and toolkit developed and maintained by OBEO and AtlanMod. It was initiated by the AtlanMod team. In the field of Model-Driven Engineering (MDE), ATL provides ways to produce a set of target models from a set of source models.
QVT (Query/View/Transformation) is a standard set of languages for model transformation defined by the Object Management Group.
A model transformation language in systems and software engineering is a language intended specifically for model transformation.
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The Business Process Definition Metamodel (BPDM) is a standard definition of concepts used to express business process models, adopted by the OMG. Metamodels define concepts, relationships, and semantics for exchange of user models between different modeling tools. The exchange format is defined by XSD and XMI, a specification for transformation of OMG metamodels to XML. Pursuant to the OMG's policies, the metamodel is the result of an open process involving submissions by member organizations, following a Request for Proposal (RFP) issued in 2003. BPDM was adopted in initial form in July 2007, and finalized in July 2008.
Knowledge Discovery Metamodel (KDM) is a publicly available specification from the Object Management Group (OMG). KDM is a common intermediate representation for existing software systems and their operating environments, that defines common metadata required for deep semantic integration of Application Lifecycle Management tools. KDM was designed as the OMG's foundation for software modernization, IT portfolio management and software assurance. KDM uses OMG's Meta-Object Facility to define an XMI interchange format between tools that work with existing software as well as an abstract interface (API) for the next-generation assurance and modernization tools. KDM standardizes existing approaches to knowledge discovery in software engineering artifacts, also known as software mining.
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