An Introduction to Synchronous Grammars

Synchronous context-free grammars are a generalization of context-free grammars (CFGs) that generate pairs of related strings instead of single strings. Thus they are useful in many situations where one might want to specify a recursive relationship between two languages. Originally, they were developed in the late 1960s for programming-language compilation [1]. In natural language processing, they have been used for machine translation [19, 20, 3] and (less commonly, perhaps) semantic interpretation. As a preview, consider the following English sentence and its (admittedly somewhat unnatural) equivalent in Japanese (with English glosses):