Discontinuous-constituent phrase structure grammar
Discontinuous-constituent Phrase Structure Grammar (DCPSG) (distinct from Discontinuous Phrase Structure Grammar/DPSG) is a formalism for describing discontinuous phrase structures in natural language, such as verb phrases in VSO languages. The formalism was introduced in the slightly more constrained form of Discontinuous-constituent Phrase Structure Grammar with Subscripts and Deletes (DCPSGsd) in Harman (1963). DCPSGs describe a superset of the context-free languages, by means of rewrite rules that permit a limited amount of wrapping, similar to that found in Head 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 formula_1 where formula_2 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 formula_1, an occurrence of formula_4 may be rewritten as formula_2. For rules with an underscore, the rewrite semantics are slightly different: given a rule formula_6, an occurrence of formula_4 can be rewritten as formula_2, with formula_9 being  inserted immediately after the next non-terminal that is introduced at the same time. Using strict left-most productions, formula_9 is simply inserted immediately after the non-terminal that follows formula_4 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: