ELU: an Environment for Machine Translation

L Introduction We present here ELU, 1 all environment for research in computational linguistics, and, in particular, machine u'anslation. As its name indicates, ELU is one of the growing number of systems designed to employ unification as the principal computational mechanism; we shall mention below some respects in which it difl~rs from other such systems. In addition to investigations of MT techniques, ISSCO has been involved in research on evaluation of MT systems (cf. King and Falkedal, 1990). The basic assumption underlying work on ELU is that the nature of (machine) translation is as shown in Figure 1 below-distinct grammars encoding language-specific infommdon, and defining a relation between texts and representations, used in conjunction with a mechanism for transforming these representa-representations representations Transfer mapping between representations Figure 1: Translation As will be apparent, the facilities provided in ELU have been strongly influenced by this view. 2. ELU ELU exploits the parser and unifier of UD (Johnson and Rosner, 1989), but differs from that earlier system in the addition of a generator (Russell et al., 1990) and a transfer component (Estival et al., 1990; Russell et al., 1989). ELU may be thought of as an enhanced PATR-II style environment for linguistic development. Throughout the system, including the transfer component, the syntax of the ELU language follows rather closely the PATR formalism which has become a standard for unification-based systems (Shieber, 1986). An environment of this kind is both a computational tool, and a formalism for representing linguistic knowledge, and we will consider ELU under those two aspects: • as a computational work environment which provides • a language for stating linguistic descriptions. The characteristics of ELU as a computational tool for linguistic development and applications derive from its clear and well-defined formalism, which allows the representation of linguistic knowledge independently of any particular machine or application. Some properties of the system are worth emphasizing-it is: • machine independent: ELU is a Common LISP program, and requires no specific interface, and • general purpose: ELU is designed as a computational tool suitable for a large range of linguistic applications, such as: • the description of differing aspects of a particular language: lexical, morphological, syntactic, or semantic. • a specific task such as parsing or generating natural language texts or transfer between feature-structures (e.g. to map a range of logically equivalent representations to a canonical form, cf. Russell et al. (1989)). • translation, …