Global index grammar
Global index grammars (GIGs) are a class of grammars introduced in Castaño (2004) in order to model a number of phenomena, including natural language grammar and genome grammar. The easiest description of GIGs is by comparison to Indexed grammars. Whereas in indexed grammars, a stack of indices is associated with each nonterminal symbol, and can vary from one to another depending on the course of the derivation, in a GIG, there is a single global index stack that is manipulated in the course of the derivation. Because of the existence of a global stack, a GIG derivation is considered complete when there are no non-terminal symbols left to be rewritten, and the stack is empty.