Modularisation can reduce the effort in designing and maintaining language specifications. Existing approaches to language modularisation are typically either focused on language syntax or on language semantics. In this paper, we propose a modularisation approach covering both syntax and semantics. We propose defining composition rules on the level of abstract syntax, making it the central artefact in a language module. To enable clean interfaces for such language modules—effectively making them language components—we use role-modelling at the metamodel level.
We discuss how role-based metamodelling supports the aspectual modularisation of language semantics and can also be integrated with concrete syntax specifications to build self-contained language components. We present the implementation of our approach in the LanGems language compositions system and show how it can be used to provide a modularised definition of the Object Constraint Language.