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Concepts and Implementation

Visual expressions are represented as trees in VL-Eli. A context free grammar defines the structure of such trees. Nodes of the tree can hold attributes of arbitrary types. Further, they can hold cross references to other tree nodes.

Visual representations are computed out of the abstract tree by an attribute evaluator. Modifications of such a visual representation leads in turn to a change of the underlying abstract structure. Not only the computation of visual representations, but also structural transformation, analysis and translation is specified by attribute evaluators.

There are libraries of reusable specifications for commonly-encountered subtasks, which are called specification modules. They can be combined and adapted to the actual needs in a flexible manner. In the problem domain of editor implementation specification modules encapsulate so called visual patterns. The concept of visual patterns allows the language designer to reuse and combine common visual constructs on a high level of abstraction. In many cases, visual languages can be completely implemented by application of visual patterns.

A visual patterns does not only encapsulate properties of a visual representation, it also encapsulates specialized interaction and layout mechanisms. So, our specification technique has the potential to generate intuitive and user-friendly editors.

Our implementation is based on the Eli system. In this way, all Eli tools for analysis and transformation can be reused. Tcl/Tk is used to implement the user interface. Further, the constraint solver Parcon is integrated. VL-Eli consists of 8000 lines for Tcl scripts, 1000 lines of Shell scripts, 5000 lines specifying the specification language vtree, and a 12000 lines for the implementation for some visual patterns.

Publications

SPKF02: Carsten Schmidt, Peter Pfahler, Uwe Kastens, und Carsten Fischer. SIMtelligence Designer/J: A Visual Language to Specify SIM Toolkit Applications. In Proceedings of Second Workshop on Demain Specific Visual Languages (OOPSLA 2002), Seattle, WA, USA, 2002.
KS02: Uwe Kastens und Carsten Schmidt. VL-Eli: A Generator for Visual Languages. In Mark van den Brand und Ralf Lämmel, Hrsg., Electronic Notes in Theoretical Computer Science, Band 65. Elsevier Science Publishers, 2002.
SK02: Carsten Schmidt und Uwe Kastens. Implementation of Visual Languages using Pattern-based Specifications. Technischer Bericht, Reihe Informatik tr-ri-02-233, Universität Paderborn Fachbereich Mathematik-Informatik, 2002.
JKSS01: Matthias Jung, Uwe Kastens, Christian Schindler, und Carsten Schmidt. Visual Pattern in the VLEli System. In Reinhard Wilhelm, Hrsg., Proceedings 7th International Conference on Compiler Construction CC'2001, Nummer 2027 in Lecture Notes in Computer Science, S. 361-364. Springer Verlag, April 2001.
Jun00: Matthias Jung. Ein Generator zur Entwicklung visueller Sprachen. Dissertation, Universität Paderborn, November 2000.
JKSS00a: Matthias Jung, Uwe Kastens, Christian Schindler, und Carsten Schmidt. Visual Languages: Generating Structure-Editors from Pattern-Based Specifications. Technischer Bericht, Reihe Informatik tr-ri-00-214, Universität Paderborn Fachbereich Mathematik-Informatik, Oktober 2000.
JKSS00b: Matthias Jung, Uwe Kastens, Christian Schindler, und Carsten Schmidt. A Pattern-Based Generator for Implementation of Visual Languages. In Proceedings 2000 IEEE International Symposium on Visual Languages, S. 71-72, Seattle, Washington, September 2000. IEEE Computer Society Press.
SS00: Carsten Schmidt und Christian Schindler. Muster-basierte Generierung von Struktur-Editoren für visuelle Sprachen. Diplomarbeit, Universität Paderborn, Germany, Januar 2000.

A complete, possibly more up-to-date list of the working group's publications is available at the publications page.