Domain Specific Languages (DSLs) have always played a role in Product Line Engineering. However,  they haven't been used much in the Product Line Engineering (PLE) mainstream. I think this is a mistake. DSLs are able to precisely and concisely describe the way a system works. By defining a specific DSL for a particular problem domain, application developers have a very powerful tool at their hand.

This keynote will briefly describe DSLs and how they fit into PLE. Then the concept of language workbenches will be introduced. Language workbenches aim at bringing programming and modeling onto the same tooling infrastructure, promising a merger of what has traditionally been called modeling and programming.

Finally, I will discuss the idea of modular languages. Instead of building big languages that contain every possible feature on earth, you build language modules which you then include in your programs only if you need them. Several language workbenches support meaningful language modularization, making this approach feasible. In a very real way, this will lead to Product Line Engineering for programming languages.