Metarules

Metarules are used in Generalized Phrase Structure Grammar to capture structural generalizations in a similar way transformational rules did in earley transformational grammar. Unlike transformational rules they don't map structural description onto (new) structural descriptions, but generate new lexical ID rules on the basis of given ones.

Example
The Passive Metarule is used to generate for each VP-rule introducing a transitive verb a new lexical ID rule which introduces a passive verb form accompanied by the same phrases, except that the direct object replaced by an optional PP:

VP $$\rightarrow$$ W, NP $$\Rightarrow $$ VP[PAS] $$\rightarrow$$ W, (PP[by])

The Complement Omission Metarule deletes the complements of a noun,

[+N, BAR 1] $$\rightarrow$$ N, W $$\Rightarrow $$ [+N, BAR 1] $$\rightarrow$$ N

accounting for the fact that (in English) the arguments of a noun are optional.

W is a variable ranging over a multiset of categories.

Other Languages

 * German Metaregeln