Discontinuous constituent phrase structure grammar

Description

Rewrite rules of a DCPSG are identical to those of a CFG, with the addition of a meta-symbol, denoted here as an underscore. DCPSG rules therefore have the general form X → α where α is a string of terminal symbols and/or non-terminal symbols and at most one underscore.

The rewrite semantics of DCPSG are identical as those of a CFG when the rule being used does not contain an underscore: given a rule X → α , an occurrence of X may be rewritten as α .

For rules with an underscore, the rewrite semantics are slightly different: given a rule X → α _ β , an occurrence of X can be rewritten as α , with β being inserted immediately after the next non-terminal that is introduced at the same time. Using strict left-most productions, β is simply inserted immediately after the non-terminal that follows X prior to the rewrite.

Example

We can characterize the gross sentence structure of a VSO language such as Irish with the following rules (substituting English words for Irish words, and using subscripts solely for demonstration of discontinuity):

A derivation for the sentence saw John Susan, where John is the subject, and Susan is the direct object forming a VP with saw is: