Constraint Grammar (CG) parsers are at the core of most of VISL's live
applications. The Constraint Grammar concept was launched by Fred
Karlsson in the early 90'ies (Karlsson et.al.1995), and CG parsers have
since been written for a large variety of languages, routinely achieving
F-scores for PoS (word class) of over 99%. A number of syntactic CG
systems have reported F-scores of around 95%. VISL's own Constraint
Grammar systems are inspired by Eckhard Bick's PALAVRAS parser for
Portuguese (Bick 2000), and use, as a novelty, subclause function,
generalized dependency markers and semantic prototype tags. For most
languages, a lexicon based morphological analyzer provides input to the
first CG level, while the output of the last CG-level can be converted
into syntactic tree structures by specially designed Phrase Structure
Grammars (PSG's), using syntactic functions, not words, as terminals.
Other, hybrid combinations are, however, feasible. Thus, the French
system uses PoS information from a probabilistic tagger.