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Global index grammars (GIGs) are a class of grammars introduced in Castaño (2004)〔Castaño, José M. 2004. ''Global Index Languages''. Dissertation, Brandeis University.〕 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 (which is strictly leftmost for any rewrite operation that pushes a symbol to the stack). 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. ==Rule Description== GIG rules come in essentially four forms: rules that do something unconditionally, rules that do something conditioned on the topmost symbol of the stack, rules that push to the stack, and rules that pop from the stack. We can notate these in turn as: x \alpha | ''(unconditionally rewrite A as and push f to the stack)'' |- | 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Global index grammar」の詳細全文を読む スポンサード リンク
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