Tuesday, January 08, 2008

Dynamic and Domain Specific Languages in a Language Tiered Structure?

In a recent post I linked to a paper that I composed for a graduate class on Dynamic Languages in software development. Today, at InfoQ there was an interesting review of a post by JRuby developer Ola Bini. In a similar view to n-tier layered architecture, Bini describes language types of static, dynamic, and domain specific in a layered fashion.

For example, in an n-tiered layered architecture you would have a presentation tier on top of a business logic tier which is over a data layer. Bini states:
The first layer is what I called the stable layer. It's not a very large part of the application in terms of functionality. But it's the part that everything else builds on top off, and is as such a very important part of it. This layer is the layer where static type safety will really help. Currently, Java is really the only choice for this layer.
This layer corresponds to the data layer mentioned above.

The next tier Bini mentions is the dynamic language layer:
This is where maybe half the application code resides. The language types here are predominantly dynamic, strongly typed languages running on the JVM, like JRuby, Rhino and Jython. This is also the layer where I have spent most of my time lately, with JRuby and so on. It's a nice and productive place to be, and obviously, with my fascination for JVM languages, I believe that it's the interplay between this layer and the stable layer that is really powerful.
In my paper that I referenced above, I discussed that Groovy has great potential given it is designed for the JVM. Here I see this corresponding to the business logic layer.

The last tier mentioned is the Domain Specific Language (DSL) layer. For a discussion on that, go here. Bini states:
The third layer is the domain layer. It should be implemented in DSL's, one or many depending on the needs of the system. In most cases it's probably enough to implement it as an internal DSL within the dynamic layer, and in those cases the second and third layer are not as easily distinguishable.
Finally, in my view, this tier corresponds to the presentation layer. In a similar manner, the business logic and presentation tiers in many applications are often tightly coupled and "are not as easily distinguishable" as they should be. In any event, Bini’s post is an interesting perspective on the use and place for both dynamic and DSL languages.

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