• a feature-constraint-based grammar formalism
• an efficient parser for this grammar formalism
• a grammar developement environment

The YAP grammar formalism which is documented in the YAP manual has some resemblance to the HPSG formalism. It is simpler than HPSG, however, and it is based on phrase structure rules rather than principles. YAP has been used to develop a large-coverage English grammar (see article).

YAP can be used for

• parsing with feature-structure based grammars
• development of feature-structure based grammars
• development of context-free grammars by compilation of a restricted form of grammars

A version of YAP which was compiled for Sun Sparc stations (Solaris 2.6) can be downloaded here as a gzip-compressed tar file. It is freely avaliable for education, research and other non-commercial purposes.