Finally M0 level represents data of a specific model.
MOF.Metamodel:.Open. Issue
The architecture proposed by OMG is very helpful to obtain a meta-model of BPMN
notation, but in our study we highlight some problems related to the language in
the M3 level strictly related to UML that impose some limits when used to define
metamodel.
The first problem is about the metamodel semantics: It is very important to assign
a meaning to every metamodel concept in order to have the meaning of each methodology
primitive. In MOF approach the use of stereotypes to define primitives
which are not directly supported by UML is intensive: A lot of primitives are not
directly supported by UML and, thus, all primitives are represented by stereotypes.
Metamodel semantics, consequently, coincide with stereotype semantics. Furthermore,
the lack of semantics creates confusion to the unskilled designer during the
practical applications of modeling concepts. The explicit presence of semantics helps
the designer to understand how the modeling concepts should be used.
Another problem strictly connected to semantics concerns semantic relationships
among classes: MOF allows us to use only two relationships: aggregation and association.
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