Catalogue of Artificial Intelligence Techniques
Generalised Phrase Structure Grammar
Keywords: LFG, Lexical Functional Grammar, Transformational Grammar
Categories: Natural Language
Author(s): Alan W. Black
The GPSG was a move away from the more traditional computational syntactic framework of Transformational Grammar. The main theoretical point of this formalism is that it is equivalent to Context-free Grammars. The formalism differs from conventional phrase structure grammars in that it:
- Describes syntactic categories in terms of lists of feature and value pairs, e.g., [N +, V -, AGR [PER 3, PLU -]] to represent a third person singular noun.
- Instead of conventional mother and daughters type rule, two equivalent notations are used: Immediate Dominance (ID) specifying which categories can dominate which daughters; and Linear Precedence (LP) rules specifying the order of these daughters.
- Feature passing conventions, specify default `copying' of features up and down the parse tree.
- Meta-rules can be used to define new ID/LP rules from other existing ones thus the meta-rules, and basic ID/LP rules effectively specify, if compiled out, a set of context free grammar rules.
- Gazdar, G., Klein, E., Pullum, F. and Sag, I. , Generalised Phrase Structure Grammar
, Blackwell, Oxford, 1985.