Domain Specific Languages

This is the last day of the conference part of JAOO, tomorrow is a full day tutorial.

Today I've been mostly listening to talks about Domain Specific Languages. This is a notion that kind of is the next step from Domain Driven Development, but also requires something more to quite get there. I think the stuff that we're trying to do with DDD is the closest thing we can get to an "internal" DSL in Java (to use Martin Fowlers classification), without actually making a full-blown DSL.

Now, what is a full-blown DSL? A DSL is a specific syntax, typically for a small, well defined domain, aimed at making the software more expressive. For a more through description read Martin Fowlers article on Language Workbenches. Usually, a DSL, whether internal or external, will imply some kind of transformation into executable code, so in that sense what we do directly in Java is not exactly DSL by strict definition. Even so it is possible to make the argument that it is.

Language Oriented Programming is a term used on the style of programming promoted by the Language Workbenches and similar technologies. LOP uses multiple DSLs to create full programs. This is analogous to Eric Evans notion of different domains within an application.

Another topic that propped up towards the end of the DSL track as a side effect is our use of the word Model and what this means to different people. And that will be the subject of my next post.