Xtext provides you with a powerful IDE and a rich featured text editor for your domain-specific language with little effort. But sometimes, a picture says more than a thousand words: You want to have some additional graphical representation of your models, a set of diagrams.
Diagrams are superior to code when it comes to high-level views. But while programmers can easily cope with files that contain several hundred lines of code, the same amount of information usually blows a diagram and destroys all its suggestiveness. Diagrams with just a few nodes and edges showing on a certain aspect of the models only are best fit for human readers. Such aspects are often spread across various model files. So in order to add the best value for the language users on top of an Xtext infrastructure, we need to allow them to create multiple diagrams, each highlighting just a subset of model information, picked from multiple model files. In other words, diagrams that have a completely different structure than their associated textual models.
Traditional graphical editing frameworks focus on editing the underling model through the diagram.
But synchronizing the model changes from textual and diagram editors is very hard if their content's structures differ. In most cases, the integration will lead to major usability quirks like unexpected editor behavior, forced save operations, blocked editors or even data loss.
So rather than working around the hard challenges of integrating graphical and textual model editing, we can leave model modification to Xtext. For the graphical stuff we can concentrate on diagram editing and leave the underlying model read-only. This way we can spend our energy on the things that really matter to the user, like easy and useful ways to populate diagrams or best visual appearance.
In Eclipse, one could build such graphical views using Zest or GEF. If model and diagram do not differ too much in structure, a small code generator targeting GraphViz is a very simple solution with high quality output.
The general integration with Xtext is covered in a follow up post.
The following screencast shows another solution for an Xtext-based domain model language. The graphical editor is using FXDiagram, a diagram framework based on JavaFX. FXDiagram offers a very smooth user experience, excellent rendering, support for touch-pad gestures, animated undo/redo, diagram persistence, export to scalable vector graphics and much more. If you are interested in learning more, feel free to contact me.