Model-Driven Engineering (MDE) proposes to modularize complex software-intensive systems using multiple models where each module serves a specific concern. These concerns of a system might be diverse and the use of multiple heterogeneous models often becomes inevitable. These models adhere to different paradigms and use distinct formalisms, which makes it hard to ensure consistency among them. Moreover, these models might contain certain concepts (at times overlapping) that are reused for building cross-concern views/models. Maintaining models using separation of concerns in a heterogeneous modeling space becomes difficult. Traditional MDE suggests the use of model transformations to maintain the mappings between heterogeneous models. In this paper, we introduce a different approach based on model federation to map heterogeneous models. In contrast to traditional approaches where heterogeneous models are gathered in a single technological space, model federation keeps them in their own technological spaces. We provide a mechanism so that elements of these models are accessible for the development of cross-concern views/models from their respective technological spaces.

Mostly the development of domain specific modeling languages (DSML) follows the traditional model driven engineering practices. First the syntax and semantics of the language are defined (at meta-level) and then it is used for the development of user models. In certain situations, it is hard even to conceptualize the demands of the user, let alone the definition of the language. Agile methods for software development suggest that the development activities should be performed alongside a client stakeholder for incremental development of the system. This approach helps in the elicitation of requirements in parallel to the actual development of the system. We followed this approach for developing a domain specific modeling language and its tooling for a local government project, Brest Métropole. The project aimed at filling the communication gap between the elected representatives (politicians) and the bureaucracy (government officers). We used a modeling methodology that does not restrict a modeler's interaction to a single abstraction level. Thus a modeler can develop both models and metamodels at the same time, where the definition of one helps in defining the other. In this article, we explain our experiences from this project and share the lessons learnt.

Software development projects seeking a high level of accuracy reach out to formal methods as early as the requirements engineering phase. However the client perspective of the future system is presented in an informal requirements document. The gap between the formal and informal approaches (and the artifacts used and produced by them) adds further complexity to an already rigorous task of software development. Our goal is to bridge this gap through a fine-grained level of traceability between the client-side informal requirements document to the developer-side formal specifications using a semi-formal modeling technique, model federation. Such a level of traceability can be exploited by the requirements engineering process for performing different actions that involve either or both these informal and formal artifacts. The effort and time consumed in developing such a level of traceability pays back in the later phases of a development project. For example, one can accurately narrow down the requirements responsible for an inconsistency in proof obligations during the analysis phase. We illustrate our approach using a running example from a landing gear system case study.