Information Technology Reference
In-Depth Information
tions [97]. The metamodel of a transformation corresponds to the language
in which the transformation is written.
The initial discussions of model-driven transformations focused on trans-
formations that are one-to-one, with each transformation linking precisely one
source to one target. In general, however, the development of structured spec-
ifications leads to more intricate patterns, where the transformations are typ-
ically many-to-many. One common pattern involves weaving multiple pieces
of specification together to yield a single target. Another is the derivation
of a number of implementation elements from a single design, yielding, for
example, both executable code and deployment control files, such as tailored
sets of firewall rules.
Another important use of model transformations is to define bridges be-
tween technical spaces or even semantic domains. For example, model trans-
formations can be used to translate specifications written in UML4ODP into
their corresponding specifications in Maude or in Alloy, in order to make use
of the analysis facilities and tools available in these target domains. Further-
more, model transformations are extensively used nowadays to build two-way
bridges between systems or applications that use disparate technologies or live
in different technical spaces (such as EMF [55], CORBA, Java or RDBMS, to
name but a few).
Finally, it is important to mention that model transformations are not
normally defined in isolation, but as part of a set of transformations that are
composed together into a model transformation chain that provides a more
powerful piece of functionality. This follows the typical pipelined approach
used, for instance, by the Unix shells, in which several commands are chained
together using pipes to form a specialized application.
15.5
Languages for Transformations
Having an architecture for transformations is not much good without
a corresponding language for defining them. The OMG has therefore de-
fined a recommendation known as QVT, or Meta Object Facility (MOF) 2.0
Query/View/Transformation Specification in full [41]. This provides a spec-
ification toolkit with a range of features for transformation specifiers with
differing requirements.
One of the ongoing debates about the use of transformations has been
whether they should be defined in a declarative or imperative style. Some
claim that a declarative style is more suited to the expression of architectural
relationships because it is more abstract, while others prefer an imperative
approach as being easier to write and debug. QVT supports both styles
by providing two different languages, called QVT Relations and QVT Op-
