Two strings γ, γ ∈ V * I are synchronous if each index in index(γ) occurs only once in γ, each index in index(γ ) occurs only once in γ , and index(γ) = index(γ ).
synchronous strings have the general form T are finite, disjoint sets of nonterminal and terminal symbols, respectively, S ∈ V N is the start symbol and P is a finite set of synchronous productions, each of the form Based on an example from (Yamada and Knight, 2001), we provide a sample SCFG fragment translating from English to Japanese, specified by means of the following synchronous productions: Note that in production s 2 above, the nonterminals VB and TO generated from nonterminal VB2 in the English component are inverted in the Japanese component, where some additional lexical material is also added.