November 15, 2007


The next student presentation in our seminar was about DiaGen, the diagram editor generator developed at our department. It was also held on October 25, 2007.

The main advantages of DiaGen editors are (from my point of view):

  • combination of free-hand editing and syntax-directed editing

  • on-line syntax checks of diagrams during the editing process, partially correct diagrams as intermediate steps are perfectly normal

DiaGen provides an editor framework as well as a so-called Designer for the specification of diagram editors. The editor developer specifies the editor (language), generates editor-specific code and together with the DiaGen editor framework a fully-fledged diagram editor can be launched immediately.

The editing process is not half as difficult as it may look at a first sight :-), so read on. The editor user draws components freely on the screen. In a first step the so-called modeler maps the diagram to its hypergraph representation as already mentioned in the last post. This hypergraph model already incorporates spatial relations as edges, e.g. to indicate, that a particular component is contained in another one. The next step is the reducer. In order to understand the reducer an analogy from string parsing is handy. Think of it as a lexer that provides a more abstract representation of the hypergraph model. The last important step is parsing the reduced hypergraph model and giving the user visual feedback about correct parts and errors. Parsing is done according to a hypergraph grammar as explained in the last post about Hyperedge Replacement Graph Grammars.

For motivational purposes here you can see an image of a DiaGen editor for flowcharts.

Further reading:

  • DiaGen Website

  • Concepts and realization of a diagram editor generator based on hypergraph transformation, Mark Minas, 2002, Science of Computer Programming, 44(2):157-180

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