Type-inheritance Combinatory Categorial Grammar

Type-inheritance Combinatory Categorial Grammar John Beavers CSLI, Stanford University Stanford, CA, 94305 jbeavers@csli.stanford.edu Abstract In this paper I outline Type-inheritance Combi- natory Categorial Grammar (TCCG), an imple- mented feature structure based CCG fragment of English. TCCG combines the fully lexical nature of CCG with the type-inheritance hierar- chies and complex feature structures of Head- driven Phrase Structure Grammars (HPSG). The result is a CCG/HPSG hybrid that com- bines linguistic generalizations previously only statable in one theory or the other, even extend- ing the set of statable generalizations to those not easily captured by either theory. 1 Introduction Type-inheritance Combinatory Categorial Gram- mar (TCCG) is a type-inheritance, unification-based CCG of the English fragment in Sag and Wa- sow (1999), implemented in the LKB (Copestake, 2002), a grammar development platform for pro- ducing efficient grammars for deep parsing. Typ- ically, work in CCG (Steedman, 1996, 2000, in- ter alia) has focused on theoretical issues such as constituency and a principled syntax/semantics in- terface, with less work spent on the organization of grammatical information (see Baldridge 2002). Work in HPSG (Pollard and Sag, 1994; Ginzburg and Sag, 2000, inter alia) has instead focused on well-grounded structuring of grammatical informa- tion, most specifically in terms of type-inheritance hierarchies, although often at the cost of coverage and elegance (see Penn and Hoetmer 2003). How- ever, the respective foci of work in these frame- works are largely orthogonal, suggesting a great po- tential in combining them, as recent work by Villav- icencio (2001) and Baldridge (2002) has demon- strated. Following directly on this work, I adopt the type hierarchies of HPSG wholesale into TCCG, ex- ploring directly the theoretical advantages this hy- brid approach yields, with direct comparison to pre- vious CCG and HPSG work. A full description of TCCG is beyond the scope of this paper (see Beavers 2002); I sketch below just a few of its ad- vantages. In � 2 I discuss background information about encoding TCCG in the LKB, including how TCCG deals with the so-called “spurious ambigu- ity” problem of CCG. In � 3 I compare the rele- vant features of HPSG and CCG and discuss pre- vious work that has combined them. In � 4 I discuss the advantages type hierarchies bring to CCG, us- ing the structure of the lexicon as well as the struc- ture of lexical mapping rules as case studies. In � 5 I discuss the advantages of CCG’s highly lexical- ist nature over common HPSG analyses and how these are encoded in TCCG. In � 6 I discuss one domain (modification) where TCCG shows poten- tial to simplify common analyses in both HPSG and CCG grammars due to its hybrid nature. 2 Implementation Details I assume for this paper a rudimentary understand- ing of CCG. TCCG encodes as usual a small set of simplex syntactic categories (S, N, NP, PP, and CONJ) from which complex categories are built via slash operators. For example, eat is assigned cate- gory (S � NP) � NP, i.e. eat …

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