Editing Unified Modeling Language (section)

== Metamodeling ==
{{Main|Meta-Object Facility}}

[[File:M0-m3.png|thumb|320px|Illustration of the Meta-Object Facility]]

The [[Object Management Group]] (OMG) has developed a [[metamodeling]] architecture to define the UML, called the [[Meta-Object Facility]].<ref>Iman Poernomo (2006) "[http://calcium.dcs.kcl.ac.uk/1259/1/acm-paper.pdf The Meta-Object Facility Typed] {{Webarchive|url=https://web.archive.org/web/20160630002118/http://calcium.dcs.kcl.ac.uk/1259/1/acm-paper.pdf |date=30 June 2016 }}" in: ''Proceeding SAC '06 Proceedings of the 2006 ACM symposium on Applied computing''. pp. 1845–1849</ref> MOF is designed as a four-layered architecture, as shown in the image at right. It provides a meta-meta model at the top, called the M3 layer. This M3-model is the language used by Meta-Object Facility to build metamodels, called M2-models.

The most prominent example of a Layer 2 Meta-Object Facility model is the UML metamodel, which 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 runtime instances of the system.<ref>{{cite web|url=http://www.omg.org/spec/UML/2.4.1/Infrastructure/PDF/ |title=UML 2.4.1 Infrastructure |publisher=Omg.org |date=2011-08-05 |access-date=2014-04-10}}</ref>

The meta-model can be extended using a mechanism called [[stereotype (UML)|stereotyping]]. This has been criticized as being insufficient/untenable by [[Brian Henderson-Sellers]] and Cesar Gonzalez-Perez in "Uses and Abuses of the Stereotype Mechanism in UML 1.x and 2.0".<ref name="UsesAbusesStereotype">{{cite journal
|author1=[[Brian Henderson-Sellers]]
|author2=Cesar Gonzalez-Perez
|title=Uses and abuses of the stereotype mechanism in UML 1.x and 2.0
|date=October 1, 2006
|journal=MoDELS '06: Proceedings of the 9th International Conference on Model Driven Engineering Languages and Systems
|pages=16–26
|doi=10.1007/11880240_2
|publisher=[[Springer-Verlag]]
|series=[[Lecture Notes in Computer Science]] 4199
|volume=4199
|location=[[Berlin]], Germany|isbn=978-3-540-45772-5
}}</ref>