Auxiliary Models

This is an architectural pattern.


Decompose a transformation sequentially by introducing a new auxiliary or intermediate model to simplify transformation processing.

Application conditions

This pattern can be applied to simplify transformations which operate on complex input models by adding a preliminary transformation which produces an intermediate representation upon which the main transformation can more effectively operate (e.g., by deriving a semantically-oriented representation from a syntax-oriented representation, or by re-expressing some complex constructs in terms of simpler ones). It may also be introduced to facilitate evolution of a transformation to adapt an existing transformation to an enlarged source metamodel without changing the existing transformation.

It can be used to sequentially decompose a transformation into subtransformations which can be specified and implemented using different transformation languages and technologies, appropriate for the subtransformations.


Introduce an intermediate language S1 and divide tau into a preliminary transformation tau1 which produces an intermediate auxiliary model m1 : S1, and a main transformation tau2 operating on m1 : S1 to achieve the effect of the original transformation:


The transformation is made more modular and its processing is potentially simplified. The auxiliary model may be used by additional transformations.


Model management is complicated by the additional model and metamodel.

Applications and examples

The concept of an intermediate language or interlingua is an example of this pattern, whereby M*N pairwise mappings between M sources and N targets are replaced by M mappings from the sources to a common intermediate representation, and N mappings from this representation to the targets.

An example is given in (Paige et al., 2010) of an application of this pattern, to factor a complex UML-to-PROMELA translation into two sequential steps, using a simplified intermediate representation of the UML source model semantics to facilitate the translation.

A UML to Java translation could be simplified by using a preliminary stage to reduce complex constructs such as association classes or multiple inheritance to constructs in a simpler UML sublanguage which can be more directly mapped to Java. In the UML-RSDS toolset, the translation from UML to B uses an intermediate representation in a metamodel for B, as an intermediate step in generating B textual models. The translation from UML to Java uses an intermediate activity model representation, this activity model is also used as the source for mappings to C\# and C++.

Related patterns

The pattern is a further progression of Auxiliary Metamodel: in Auxiliary Metamodel the auxiliary metamodel language is used internally within a transformation, whilst in this pattern it is defined externally as a separate language which is used as an input and output for subtransformations of the transformation.

The Model-Driven Architecture (MDA) concept of successive PIM to PSM and PSM to code transformations is related to this pattern.

(Paige et al., 2010) E. Guerra, J. de Lara, D. Kolovos, R. Paige, O. Marchi dos Santos, transML: A family of languages to model model transformations, MODELS 2010, LNCS vol. 6394, Springer-Verlag, 2010.