Applications nowadays are written using more than one language: typically some sort of general purpose language and a constellation of complementary languages (SQL, HTML, XML, Scripting languages, DSLs).
Between artefacts written in different languages there are relations of various kinds, at least references (for example some ID have to be the same in a Java file and in an XML file). The problem is that we miss a general approach to check those relations and ensure global consistency.
In our paper we discuss the problem and present a simple, preliminary approach to solve it inside language workbench. Finally we discuss a research agenda for language integration.
If you want to read the paper, the pdf is available here.