MARTIN FOWLER

Martin Fowler



Martin Fowler

Introduction

The roadmap for Martin Fowler's forthcoming book on DSLs indicates that he will focus on textual DSLs. The online draft of the intro does however briefly show a graphical language for a home security system: the model is implemented with MetaEdit+, based on the original textual requirements:

Miss Grant has a secret compartment in her bedroom that is normally locked and concealed. To open it she has to close the door, open the second draw in her chest, turn her bedside light on - and then the secret panel is unlocked for her to open.

Juha-Pekka has been using Martin's example as a way of showing how to implement a DSM language in MetaEdit+ (Parts 1 and 2 ), and in Part 3 he points out some problems with the original language: too broad a focus, unclear usage process, and too low a level of abstraction. Juha-Pekka correctly suggests going back to the basics of the domain to discover the necessary language concepts, rather than trying to shoehorn this domain into a generic state model.

As an exercise, however, I thought it might be interesting to try to improve Martin's language as it is, rather than starting from scratch. How much of DSM is "you just have to know how to do it", and how much can be reduced to simple steps that anyone could apply? Obviously, the more of the latter that we can find, the easier it is for somebody to get started. Our DSM book aimed at just this kind of practical approach; let's take a few hints from there and apply them to Martin's language. We'll show the model in the current state of the language as we evolve it: click the pictures to see the full size screenshot.

Use meaningful symbols

Miss Grant's model with meaningful ...