Check out my volume rendering page to learn more about the package I implemented and to see some pictures . I worked with the natural language processing group at the TUB in collaboration with the linguistics department. My supervisor was Prof. K. Brockhaus. In accompanying classes and colloquia we also dealt with semantic and knowledge representation issues. Tree adjoining grammars were invented by A. Joshi and M. Takahashi in 1975.
TAGs are interesting because they offer slightly more expressiveness than context free grammars.
Their inventors argue that this extra expressiveness is clearly of linguistic relevance. Indeed, there are structures in natural languages that cannot be captured by pure CFGs, but can easily be represented in the TAG formalism. Dynamik und Komplexit t, Bremen, 1995. H.C. Hege, D. Stalling, Volume Rendering on Irregular Grids , Abstract, International Workshop on Mathematics and Visualisation, Berlin 1995.