“…These include bags of words (Brown et al, 1990) and bags of complex lexical representations (Beaven, 1992;Brew, 1992;Whitelock, 1992), word lattices (Knight & Hatzivassiloglou, 1995;Langkilde & Knight, 1998;Bangalore & Rambow, 2000), and non-recursive context-free grammars (Langkilde, 2000). As will be discussed in detail in Section 2, word lattices and non-recursive context-free grammars allow encoding of precedence constraints and choice among different words, but they both lack a primitive for representing strings that are realized by combining a collection of words in an arbitrary order.…”