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The parser is implemented using a reduction of the formulation of TDG into a constraint problem stated in terms of finite sets. The reduction is more thoroughly described in (Duchier 99) (Duchier 00) and (Duchier 01). Parsing amounts to searching for solutions of the CSP which describes the valid TDG analyses for a given input. Thereby, we apply alternating propagation and distribution steps (note: distribution can be optionally turned off). With the help of the selection constraint, we achieve very strong propagation. In fact, in many cases no search at all is necessary, in spite of substantial lexical and structural ambiguity.
It is possible to switch the parser into generate mode. In generate mode, the parser regards the list of words comprising the string to parse not as a list but a bag of words. Hence, the parser finds all TDG analyses which are licensed for this bag of words. Generate mode can be used to debug a grammar: it can help finding undesired TDG analyses. It is also employed by the graphical user interface (see chapter 5) to generate the set of linearizations licensed for a bag of words.
The TDG parser allows to individually toggle each of the ID, LP and TH principles on and off which also facilitates grammar debugging.
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