loyal opposition On the Declarative Specification of Models

C olleagues in my research group and in collaborating institutions typically model software designs using graph-ical tools such as Rational Rose, Together, and Visio. I often witness them toiling to adjust a graph's appearance with the mouse or laboriously visiting each class to change a single field's type. This need not be so. Design models should be composed textually, and graphs should be automatically generated. You might find it perverse to employ two different representations (textual and graphical) for the same underlying model. So, to substantiate my view, I'll outline the advantages of graphical models and describe the benefits gained from directly manipulating a textual representation , illustrating my point using a prototype implementation. Graph-based models No rule specifies that models should appear in a graphical form. A model is a simplification of reality, so a model for a software artifact could really be an outline of that artifact; think of a class definition without code in the method bodies. However, we usually prefer to examine many of our models in a graphical representation: UML employs nine different diagrams for visualizing different perspectives of a system. Using a diagram to represent a model has several advantages. When we examine a model's graphical representation, we use our visual cognitive apparatus, which has millions of years of evolutionary advantage over our text-reading abilities. A diagram's 2D representation is a lot more expressive than text, which readers typically scan from left to right and from top to bottom. We can view diagrams from different directions to gain distinct insights, while using a larger symbol set makes them more expressive. In addition, we can obtain different levels of detail from the same diagram: a bird's-eye view will easily convey a system's structure, while examining a class in detail can reveal its collaborators. Finally, a diagram can let us identify patterns; again, 2D pattern matching is an activity we humans are particularly good at. The drawing-editor approach Designers typically create their model diagrams using a drawing editor. The semantic distance between the editor's graphical model representation and the underlying software artifact can vary enormously. Some tools, such as Visio, are purely drawing aids. Others, such as Rational Rose, offer round-trip engineering (code-to-model and model-to-code generation), while tools such as ArgoUML provide domain-specific advice during design. However, all drawing editors require you to place and manipulate shapes on the canvas, which, regardless of the help that …