Model-Driven Engineering - Model-Driven and Software Product Line Engineering - page 72

3.4. Model transformations
Model transformation appears to be one of the most
useful operations on models. Model transformations are
software artifacts that implement algorithms to transform
models conforming to source metamodels into either models
conforming to target metamodels or source code.
Figure 3.8 presents the scenario of a model transformation
with one source model and one target model. Note that (1) each
model conforms to its respective metamodel and (2) the model
transformation refers to the source and target metamodels.
Metamodels are used in model transformation to navigate
models by using transformation rules . Transformation rules
are considered as functions or procedures implementing some
transformation step. They are the smallest unit of model
transformations [CZA 06]. Finally, a transformation engine is
in charge of executing the model transformation on the source
model to derive the target model.
Transformations are equivalent to functions and procedures
in programming languages, but for models. The source
and target metamodels can be seen as the type of the
transformation. This analogy is quite complete since there are
imperative and purely functional transformations as well as
high-order transformations; besides, transformations can be
compound.
Figure 3.8. Model transformation scenario