In the framework of Head-Driven Phrase Structure Grammar (HPSG, Pollard and Sag, 1994) and other current linguistic architectures, linguistic generalizations are often conceptualized at the lexical level. Among the mechanisms for expressing such generalizations, so-called lexical rules are used for expressing so-called horizontal generalizations (cf. Meurers, 2001, and references cited therein).
Lexical rules have been conceptionalized in two distinct ways, either on a meta-level as relating lexical entries (i.e., descriptions) or on the same level as the rest of the grammar, relating lexical objects (i.e., the elements described by the lexical entries). Computationally the meta-level perspective is captured by using the lexical rules to enlarge the set of lexical entries defined in the grammar, whereas under the description-level perspective lexical rules are essentially on a par with unary phrase structure rules and are taken into account at run time. The TRALE system offers both mechanisms for implementing lexical rules. The traditional ALE mechanism for handling lexical rules described elsewhere in this manual corresponds to the meta-level interpretation of lexical entries. It uses the lexical rules at compile-time to generate new lexical entries, using a depth-bound to ensure that this step terminates. The description-level approach is implemented in the lexical rule compiler described in this chapter. It encodes the treatment of lexical rules proposed in Meurers and Minnen (1997). This chapter focuses on how to use the lexical rule compiler. A discussion of this approach to lexical rules can be found in the Reference Manual of the Lexical Rule compiler and the original paper.