MOF Overview:
MOF provides a infrastructure to model data using a neutral
language and allows the model to be represented in UML. It can
use UML to define the complex relationships we discussed in the
XML sample discussed above.
MOF also provides a layered architecture consisting of data,
models, metamodels and a single meta-metamodel. Each layer is an
abstraction of the layer below it. The lowest level is the data
layer, which comprises the actual data. Examples are database
records, application objects. The second layer is the model
layer, which describes the format and semantics of the actual
data. Examples of model layer objects are database schema model,
which represent data. The model layer is also called M1 or the
metadata layer. The third layer is the metamodel Layer also
called the M2 layer. This describes the semantics and structure
of the metadata. An example of the M2 layer is a database system
table that describes the format of a table definition. The meta-
metamodel Layer or the M3 layer provides the last layer of
abstraction. This layer describes the semantics and structure of
the meta-metadata.
Apart from providing the modeling infrastructure the MOF
provides an IDL mapping interface to help in manipulating
metadata. MOF provides an IDL mapping which in turn provides an
IDL based API. The API can be used to manipulate data contained
in the different instances of the metamodel. The MOF provides
language neutral models that capture the semantics of the system
that is being modeled. This helps system architects to work with
complex systems by visualizing the metadata available for the
system instead of knowing all the intricacies of the system.
To add more flexibility MOF provides a set of reflective API's,
which provide introspection services for manipulating complex
information. The MOF reflective API works like the Java
reflection feature of J2EE and allows information to be accessed
dynamically. The Reflective API does not need to use the API
generated by the MOF to perform IDL mapping.
OMG defines the Model Driven Architecture (MDA) with the help of
MOF. MOF provides the technology and domain metamodels that are
the used in the MDA framework. These metamodels are represented
in UML (Since MOF can use UML) and will define all aspects of
the environment from different perspectives and levels of
abstraction. The MDA can use these metamodels to model
architectures using the MDA.
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