Prolog-Embedding Typed Feature Structure Grammar (PETFSG) is a unification-based grammar formalism, which is handled by a web-based grammar tool, including a chart parser. It is intended to be of value for both research and teaching purposes. PETFSG makes it easy to integrate Prolog components into the grammar. The PETFSG grammar tool provides a HTML-based user-friendly interface. The system also provides some facilities for tracing the chart-based application of the grammar.
The syntax of the PETFSG formalism is based on Prolog term syntax. It is essentially a typed and enriched variant of Shieber's PATR-II. Typed feature structures (FSs) are the basic means for encoding linguistic information, but these allow the embedding of ordinary (untyped) Prolog terms. Prolog terms may consequently be used whenever convenient, for instance, to make semantic representations more compact, and in cases where the inventory of values is large or hard to predict (e.g. in semantics). Typing may at the same time be used to impose restrictions wherever useful. The PETFSG formalism also allows Prolog calls to be made from inside the grammar. In this way, Prolog computation can be used to take care of phenomena which can not be treated by means of FS unification. The combination of typed FSs and Prolog terms and the interaction between unification and general computation make the PETFSG formalism powerful, flexible, simple, and easy to use. PETFSG is written in SICStus Prolog.
The PETFSG formalism and system have been designed with Head-Driven Phrase Structure Grammar in mind. The type system of PETFSG is however more restrictive than some of those used in the HPSG literature.
Current version, PETFSG-II.2 (December 2002) has its own page.