Domain Specific Languages (I)

Domain Specific Languages are a relatively unknown piece of Visual Studio Extension technology. In this series of posts, I'm going to describe how to create a Domain Specific Language for modelling simple inheritance, and generating code from the model. The purpose is to do it from scratch, see the process, and understand the concepts involved. You’ll require Visual Studio 2008 Service Pack 1, and the Visual Studio SDK 1.1 to do this on your own machine.

Unlike a general purpose language such as C#, a domain-specific language is designed to handle a particular problem space, or domain. Domains can be defined in many different ways. Some domains are associated with specific industries or kinds of business (insurance domain, financial services domain, library domain). Other domains relate to specific kinds of software development (Web service components, GUI components etc.).

Typically, DSLs are created when a development team has to write similar code for different projects. For example, a team may have to develop several different insurance policy applications. The applications may use the same constructs, for example, a table that specifies the policy prices in different areas, in different ways. In a DSL, the price/area table can be a language element that is handled differently in each application.

DSLs can either be textual or graphical. An example of a textual DSL is an XML schema. Textual DSLs are difficult to develop and debug, and non-technical people may find them hard to understand. Graphical DSLs are easier to work on and easier to use for communicating with non-developers.

Domain-specific development is the process of identifying the parts of your applications that can be modelled by using a DSL, and then constructing the language and deploying it to application developers. The developers use the DSL to construct models that are specific to their applications, use the models to generate source code, and then use the source code to develop the applications.

The benefits of DSL development include:

• DSL consists of elements and relationships that directly represent the logic of the problem space. Therefore, its easier to design the application, and find and correct errors of logic.
• They let non-developers and people who do not know the domain understand the overall design.
• Developers can use the code that their model generates to quickly create a prototype application that they can show to clients.

DSL Tools let you create a DSL that has your own graphical designer and your own diagram notation, and then use the language to generate appropriate source code for each project.