Aggregate Callback: A design pattern for flexible and robust runtime model building

In modern software engineering environments, tools that use Domain-Specific Languages (DSLs) are often applied. The usual workflow of such tools is that the textual input written in the DSL is parsed and a semantic model is instantiated. This model is later passed to another software component that processes it, e.g. a model transformation, a code generator or a simulator. Building the semantic model inside the parser is often a complex task. The model must be built in such a way that the constraints of the problem domain are enforced so that the consistency of the output is guaranteed. This paper presents a design pattern, referred as Aggregate Callback that supports enforcing constraints in the model and thus helps creating correct models. We have found that the Aggregate Callback pattern is useful for tool developers that build models in their applications.