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James Pustejovsky is the author of several papers on language generation and lexical semantics. His address is: Department of Computer Science, Brandeis University, Waltham, MA 02254. E-mail: jamesp@brandeis.edu

Zellig Harris, Michael Gottfried, Thomas Ryckman, Paul Mattick Jr., Anne Daladier, T. N. Harris, and S. Harris

Dordrecht: Kluwer Academic Publishers, 1989, xiii + 590 pp.

Reviewed by Stephen B. Johnson Columbia University

There is wide agreement that domain knowledge plays an important role in natural language processing sys­tems, and, at the same time, that acquisition of domain knowledge is an extremely difficult problem. The work under review offers a rigorous method for knowledge acquisition in scientific and technical domains, based on a formal analysis of the texts written by domain experts. The set of texts in a restricted domain is known as a sublanguage. The method, which may be termed sub­language analysis, reveals a formal structure in the sentences of the texts, sublanguage formulas, which are similar to the formulas of logic, but with certain exten­sions (which will be described below).

The sublanguage formulas described by the authors constitute a form of knowledge representation, and suggest interesting possibilities for the design of flexible and expressive databases or knowledge bases. The strength of the sublanguage approach lies in basing the knowledge representation on the analysis of actual texts. The significance of this approach to computa­tional linguistics is that the initial phase of sublanguage analysis establishes a direct relationship between sur­face sentence forms and the semantic representation (formulas). This mapping serves as a basic design for text processing algorithms.

A striking feature of the book is that the authors have carried out a thorough test of their technique on real data: 14 full-length research articles from the field of immunology, published in the period 1935-1970. The formulas obtained and the methods used in producing them are given in meticulous detail. (The appendices that give examples of the formulas actually exceed the length of the narrative portion of the book). The meth­ods employed are founded on Operator Grammar (Harris 1982) and are carried out in a general theoretical

The Form of Information in Science: Analysis of an Immunology Sublanguage

framework that portrays the organization of information in natural language (Harris 1988).

A second feature that makes this book a rarity is that the analysis of the immunology texts is presented as an "experiment" with a testable hypothesis: Do the results (sequences of formulas) obtained by objective analysis of the immunology articles correlate with known changes in knowledge of the field during the given period? The documents were selected for the study by immunologists (authors T. N. Harris and S. Harris), on the basis of the historical coverage of this period of immunological research. Confirmation of the correla­tion is provided by directly comparing the formulas (appendices 1 and 2) to the historical discussion given by the immunologists (Chapter 8), and by the discussion in the first two sections of Chapter 3.

A key aspect of the sublanguage method is that it is objective, relying only on structural features of texts and not ad hoc semantic judgements. This propërty insures that the analysis is repeatable, and the authors demonstrate this fact by performing an independent analysis of French immunology reports from the same period (Appendix 2). This second analysis served to verify that the resulting sublanguage formulas were the same, regardless of the host language employed by scientists.

Chapter 1 describes the sublanguage method, a form of knowledge acquisition that has been applied primar­ily in text-processing applications (e.g., Sager et al. 1987, Sager 1986, Sager 1978, Hirschman et al. 1976) but which can be used in a more general way as a means of unearthing the information structure of a domain through analysis of texts written by experts. The last three sections of Chapter 3 define this structure using the intriguing concept of a "grammar of science." The purpose of the method is to establish classes of objects relevant in the domain, and classes of relations in which the objects participate. The technique groups different arguments of sentences (grammatical subjects or ob­jects) into a class according to their occurrence in the texts with the same operator (main verb, adjective, or preposition). Operators are grouped into classes accord­ing to their occurring with the same classes of argu­ments. When the analysis is carried out on a sample of sufficient size, argument classes are found to corre­spond to domain objects, and operator classes to do­main relations.

Chapter 2 presents the classes and formulas obtained for the immunology domain. Formulas are well-formed expressions made up of an operator class and one or more argument classes, and correspond to the "events" of a domain. The argument classes established by the authors include antibody (A), antigen (G), cell (C), tissue (T), and body part (B). Operator classes include inject (J), move (U), and present in (V). Examples of formulas and the sublanguage sentences they represent are:

G J B "antigen was injected into the foot-pads of rabbits"

A V C "antibody is found in lymphocytes"

GUT "antigen arrives by the lymph stream" The sublanguage method need not be limited to analysis of texts and can be adapted to incorporate data elicited directly from domain experts. An exciting prospect arises in automating portions of the sublanguage analy­sis, to create tools to assist the linguist in setting up classes and formulas (e.g., Hirschman et al. 1975, Sager 1975, Grishman et al. 1986), and to interact with domain experts to gather supplementary information and to confirm hypotheses made by the tools.

Chapter 4 discusses the informational properties of the formulas presented in Chapter 2. Sublanguage for­mulas are a compact notation for knowledge represen­tation that employ a number of devices to enrich the basic structure of operator-argument predication. Mod­ifiers can be placed on operator and argument classes as superscripts. On arguments, they function as unary operators or as quantifiers. Modifiers of operators in­clude negation, quantity, aspect, and direction (of movement). Subclasses of operator and argument classes are indicated by subscripts, e.g., cell (C) has subclasses lymphocyte (C,) and plasma cell (Cz). A rich set of connectives can join pairs of formulas.

Formulas can be implemented in a fairly straightfor­ward fashion using Prolog terms, relational database tables, a semantic net, an object-oriented system, or a frame-based representation. The choice of implementa­tion would obviously depend on the complexity of the sublanguage being processed and on the application that will make use of the data.

The application of Operator Grammar to sublanguage offers many exciting possibilities for text processing systems. Operator Grammar bears many similarities to Categorial Grammar and shares with combinatorial logic the avoidance of bound variables (cf. Steedman 1989). Chapter 5 describes the transformations of Op­erator Grammar used in the analysis phase to para­phrase variant sentence forms into the canonical formu­las. This does not imply that the recognition algorithm must be a traditional, inefficient transformational sys­tem. In fact, the nature of Operator Grammar encour­ages the design of algorithms which map free text directly into a structured representation (Johnson 1987). The constraints afforded by domain-specific classes are well known, and algorithms can exploit these con­straints in a simple way for considerable gains in efficiency. Chapter 7 gives an informal description of procedures for rapid recognition of formulas in free text, and for generation of English sentences from the formulas.

The book is a unique and remarkable contribution, so it goes without saying that the methods will be new to many readers, necessitating a fair amount of unfamiliar terminology. Terms are well explained and used in a clear and consistent manner, but the book suffers for