One of the key feature of the workbench is the static composition operator require . This operator allows defining these various aspects in separate units and integrating them automatically into the meta-model. The composition is done statically and the composed model is typed-checked to ensure the safe integration of all units. This mechanism makes it easy to reuse existing meta-models or to split meta-models into reusable pieces. It allows to compose the various files and models that will form the final tool.

The workbench will seamlessly convert and merge the various files into the final kermeta program. The classic inputs will be ecore files, kmt files or uml profiles files. The finala assembly will depend on the capabilities of the inputs models. For example, a ecore model has a granularity at the class level (ie. it will just add new classes) whereas Kermeta has a granularity at the feature level and thus can add new features to a class(see next section Section 1.5.2, “ Model element static introduction : Aspect-oriented language ” for more details)

TODO add a sample

One of the key features of Kermeta is the static composition operator require allows extending an existing meta-model with new elements such as properties, operations, constraints or classes. This operator allows defining these various aspects in separate units and integrating them automatically into the meta-model. The composition is done statically and the composed model is typed-checked to ensure the safe integration of all units. This mechanism makes it easy to reuse existing meta-models or to split meta-models into reusable pieces. It can be compared to the open class paradigm. Consequently a meta-class that identifies a domain concept can be extended without editing the meta-model directly. Open classes in Kermeta are used to organize cross-cutting concerns separately from the meta-model to which they belong, a key feature of aspect-oriented programming. With this mechanism, Kermeta can support the addition of new meta-class, new subclasses, new methods, new properties, new contracts to existing meta-model. The require mechanism also provides flexibility. For example, several operational semantics could be defined in separate units for a single meta-model and then alternatively composed depending on particular needs. This is the case for instance in the UML meta-model when several semantics variation points are defined.

Thank to this composition operator, Kermeta can remain a kernel platform to safely integrate all the concerns around a meta-model. This feature has proved to be extremly useful in the context of metamodel engineering.