ID/LP rules

Generalized Phrase Structure Grammar (GPSG) uses ID-rules (immediate dominance rules) and LP-rules (linear precedence rules) instead of context-free phrase structure rules to describe hierarchical and sequential aspects of linguistic units separately.

Example

Wenn man kontextfreie Phrasenstrukturregeln als Wohlgeformtheitsbedingungen für (lokale) Bäume auffasst, dann lässt eine Regel der Form X <math>\rightarrow</math> <math>Y_1</math> <math>Y_2</math> ... <math>Y_n</math> genau einen Baum zu. Für diesen Baum gilt: (a) Die Kategorie <math>X</math> dominiert die Kategorien <math>Y_1</math> ... <math>Y_n</math> und (b) Die Kategorie <math>Y_i </math> steht vor der Kategorie <math>Y_{i+1}</math> (für i = 1, ... n-1).

An ID-rule X <math>\rightarrow</math> <math>Y_1,</math> <math>Y_2,</math> ..., <math>Y_n </math> on the other hand, licences all trees in which X dominates the other categories, no matter in which order these categories appear. An LP-rule restrains the set of local trees licenced by an ID-rule: Each tree which violates this rule is considered as unadmissible.

Comment

Replacing contextfree rules by ID- and LP-rules was motivated by the idea that by this division of labor it is possible to state important generalization concerning the word order (constituent order) for a given natural language explicitly.

Each ID/LP-syntax can be converted into a strongly equivalent context-free phrase structure syntax. As the linear restrictions expressed by LP-rules are interpreted globally (no local tree licenced by any ID-rule may violate any of the LP-rules), there are context-free grammars which can not be converted into a strongly equivalent ID/LP-grammar (though into a weakly equivalent ID/LP-syntax).

Other Languages

• German ID/LP-Regeln