The Head-Driven Phrase Structure Grammar (HPSG) is a grammar theory developed by Carl Pollard and Ivan Sag 1985 in the tradition of the transformational-generative grammar. It uses a uniform formalism and is organized in a modular way which makes it attractive for Natural language processing.
A HPSG grammar includes principles and grammar rules and lexicon entries which are normally not considered to belong to a grammar.
The basic type HPSG deals with is the sign. It has two features PHON (the sound, the phonetic form) and the SYNSEM (syntactic and semantic) feature which is split into subfeatures subsequently.
Emily Bender, Ivan A. Sag, and Thomas Wasow Syntactic Theory: a formal introduction, Second Edition ([1])Books
