Book Reviews: Machine Translation: Linguistic Characteristics of MT Systems and General Methodology of Evaluation

This book (which has been long in the making! ) is a compilation of a large number of papers written over the years (1971-1981) dating from the first attempts (circa 1968) at this system. It describes in full detail TAUM (Traduction Automatique de l'Universit6 de Montrral), a second-generation transfer-based MT system, as opposed to a first-generation, direct (i.e., word-for-word) translation or a third-generation, knowledge-based (i.e., interlingua MT system). (For illustrative purposes, the authors include a detailed flowchart of a typical secondgeneration MT system in Appendix B.) In particular, this book highlights the operational system produced by the TAUM project--TAoM MI~TEO --which translates telegraphic weather reports issued by Environment Canada from English into French. (The experimental systems produced from TAUM were TAUM-71, TAUM-73, TAOM-76 and TAUM-AVIATION.) TAUM MI~TEO has been operational since 1977 and is universally acclaimed as "the closest approximation to fully automated high-quality (machine) translation among currently operational systems" (Nirenburg 1987). Because of MI~TEO'S stereotypic format, the research from this project has led to a very important development in a branch of linguistic analysis concerned with the sublanguage concept, connected with the names of Lehrberger, Richard Kittredge, and Ralph Grishman (see a discussion in Hutchins 1986). In Chapter 2, five characteristics of MT systems are identified. The first pertains to the degree of automation in the system, whether it be machine-aided human translation, human-aided machine translation, or fully automatic machine translation. Secondly, the extent to which the source language is analyzed, either locally or at the sentence level, is discussed. The authors stress the major presupposition of fully automatic (highquality) MTBthe depth of analysis of an MT system is indicative of the level of understanding implicit in the system. Next, the type of information transfer (e.g., direct or use of a pivot language) between source and target language is considered. The authors conclude that designing a universal pivot language, one that is "totally independent of any particular natural language" is not feasible. This conclusion seems somewhat dated. A recent experimental MT system KBMT-89, developed at Carnegie Mellon University (CMU-CMT 1989) for bidirectional Japanese-English translation of computer hardware manuals is based on this model. What makes KBMT-89 different from previous attempts at building such interlingual systems is its systematic reliance on a large and independently motivated model of the domain of translation, which serves as the basis for developing the inter~ingual representations. The last two system characteristics deal with the organization (and advantages) of modular MT processing and the domain dependency of the lexical and syntactic aspects of an MT system, respectively. Additionally, the authors stress the fact that the performance of an MT system depends very much on the domain of application, given its restricted vocabulary and, in some cases, a restricted syntax as well. Consequently, they leave the reader pondering if one domain is necessarily easier to translate than another. Chapter 3 takes a closer look at the characteristics of an MT system by giving an idea of its architecture in terms of the major linguistic components: lexical, morphological, syntactic, and semantic. The lexical component discusses the number and structure of dictionaries to be used and the information content and form of each lexical entry (including idioms) contained within each lexicon. The morphological component explains the processing and strategies behind inflectional, derivational, ~md compositional morphology. Simple and complex sentence structure as well as complex constituents are analyzed in the section on syntax. Because local analysis is insufficient for any reasonable level of understanding, the semantic component describes finding the total meaning of a sentence at both the word and syntagrnatic levels---resolving homography at the word level and using selectional restrictions and subcategorization information at the syntagmatic. Chapter 4 discusses two opposing approaches to designing an MT system: the corpus-based approach and the standard grammar approach. The advantages and disadvantages of each are explained. Both approaches have a direct effect on determining the content of the linguistic information present in the dictionaries and grammars of an MT system. Chapter 5 deals with the methodology for linguistic evaluation: identifying the user's needs and constraints of translation, evaluating the performance of the linguistic components of the system, and evaluating the potential of a system. Additionally, because of the effect on the human translators and revisers who must use the machine, the evaluation of the user environment is also discussed. The authors suggest steps to be followed in deciding on the acceptability of a system and then summarize the fundamental aspects and limitations of the proposed methodology for evaluating MT systems. An important feature of this book, which sets it aside