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The paper describes a Swedish-language customization (S-CLE) of the SRI Core Language Engine, which has been developed at SICS from the original English-language version by replacing English-specific modules with corresponding Swedish-language versions. The S-CLE is intended to be used as a building block in a broad range of applications, such as data-base query system, machine translation systems, NL front-ends, speech-to-text/text-to-speech systems, and so on. Examples of the first two types of application already exist. The main part of the S-CLE is an extensive Swedish grammar that is compiled into parsing and generation modules. The grammar formalism is a type of unification grammar loosely based on Generalized Phrase Structure Grammar (GPSG). Generation is performed using the Semantic-Head-Driven algorithm. Analysis turns sentences into ``Quasi-Logical Form'' (QLF), a logical-form representation, while generation works in the opposite direction. Intermediate stages include processing of morphology, syntax and semantics. For knowledge-base applications, a separate module can convert QLFs into conventional scoped logical forms. After two-and-a-half years of work (approximately 45 person months), the first prototype system has a vocabulary of about 1900 words and covers a fairly broad range of possible grammatical constructions. Based on our experience in this project, we present in this paper detailed arguments to support the claim that customization of an English-language NLP system is a highly cost-effective way of constructing Swedish language systems with corresponding functionality. A shorter version of this paper appears in L. Ahrenberg (ed.): Papers from the Third Nordic Conference on Text Comprehension in Man and Machine , Link Sweden, 1992.

The syntactic analysis component of a large-scale natural language query interface to relational data bases was greatly sped up by applying explanation-based learning(EBL), a machine learning technique. The idea is that one for most input queries can bypass the ordinary parser, instead using a set of learned rules. When no rule applies, one must pay the price of a small overhead. The set of learned rules is extracted automatically from sample queries posed by a user, thus tuning the system for that particular user. Several non-trivial problems, arising from the characteristics of the target system, were solved during the project. Measurements on a small test corpus indicated that the speed-ups when a learned rule could be used are on average a factor 30 and that the overhead, when no rule applied, is less than 3 percent. Extended version of a paper titled "Using Explanation-Based Learning to Increase Performance in a Large-Scale NL Query System" by the same authors, that was presented at the third DARPA Workshop on Speech and Natural Language, Hidden Valley, 1991. Original report number R91001.

This document is the final report for a research project aimed at producing a prototype system for on-line translation of typed dialogues between speakers of different natural languages. The work was carried out jointly by SICS and SRI Cambridge. The resulting prototype system (called Billingual Conversation Interpreter, or BCI) translates between english and Swedish in both directions.The Major components of the BCI are two copies of the SRI Core Language Engine, equipped with English and Swedish grammars respectively. These are linked by the transfer and disambiguation components. Translation takes place by analyzing the source-language sentence into Quasi Logical Form ( QLF), a linguistically motivated logical representation, transferring this into a target-language QLF, and generating a target-language sentence. When ambiguities occur that cannot be resolved automatically, they are clarified by Querying the appropriate user. The clarification dialogue presupposes no knowledge of either linguistics or the other language. The prototype system has a broad grammatical coverage, a initial vocabulary of about 1000 words together with vocabulary expansion tools, and a set of English-Swedish transfer rules. The formalism developed for coding this linguistic information make it relatively easy to extend the system. We believe that the project was successful in demonstrating the feasibility of using these techniques for interactive translation applications, and provides a sound basis for development of a large scale message translator system with potential for commercial exploitation.The main sections of this report are the following: * A non-technical introduction, summarizing the BCI's design , and containing a sample session. * An overview of the Swedish version of the CLE. * A detailed discussion of the theory and practice of QLF transfer. * A description of the interactive disambiguation method. * Suggestions for possible follow-on projects aimed in the direction of practically usable commercial systems. This is a joint report by SICS and SRI, which is publ. by both institutes. SRI Cambridge Report CCSRC-018.

This Document is an introduction to a research project aimed at producing a prototype system for on-line translation of typed dialogues between speakers of different natural languages. The work was carried out jointly by SICS and SRI Cambridge. The resulting prototype system (called Billingual Conversation Interpreter, or BCI) translates between English and Swedish in both Directions. The major components of the BCI are two copies of the SRI Core Language Engine, equipped with English and Swedish grammars respectively. These are linked by the transfer and disambiguation components. Translation takes place by analyzing the source-language sentence into Quasi Logical Form (QLF), a linguistically motivated logical representation, transferring this onto a target-language QLF, and generating a target-language sentence. We believe that the project was successful in demonstrating the feasibility of using these techniques for interactive translation applications, and provides a sound basis for development of a large scale message translator system. The final section of the paper points to several possible follow-on projects aimed in the direction of practically usable commercial systems.

We argue that bidding in the game of Contract Bridge can profitably be regarded as a micro-world suitable for experimenting with pragmatics. We sketch an analysis in which a "bidding system" is treated as the semantics of an artificial language, and show how this "language", despite its apparent simplicity, is capable of supporting a wide variety of common speech acts parallel to those in natural languages; we also argue that the reason for the relatively unsuccessful nature of previous attempts to write strong Bridge playing programs has been their failure to address the need to reason explicitly about knowledge, pragmatics, probabilities and plans. We give an overview of Pragma, a system currently under development at SICS, which embodies these ideas in concrete form, using a combination of rule-based inference, stochastic simulation, and "neural-net" learning. Examples are given illustrating the functionality of the system in its current form. Original report number R90011.

Work by Yoav Shoham advocating the use of default logic is critically examined, and several serious inconsistencies are pointed out. Shoham's analysis of the frame problem is shown to depend on a misinterpretation of the formal basis for Newtonian mechanics, and strong reasons are given to doubt the correctness of his arguments for reducing auto-epistemic reasoning to default logic. Detailed counter-examples are provided for both cases. Original report number R88009. Related paper "Did Newton Solve the Extended Prediction problem?" by M. Rayner published in Proceedings 1st Intl. Conf. on the Foundations of Knowledge Representation, R. Brachman & H. Levesque, eds., Morgan Kaufman, 1989.

We demonstrate how to reason about plans by treating them as programs expressed in a simple imperative language, and illustrate this using an example originally suggested by McCarthy and later discussed at length by McDermott. A detailed correctness proof is provided, which it is argued is greatly superior to McDermott's. Original report number R88003. Related paper, "Reasoning about Plans Represented as Procedural Programs" located in Artificial Intelligence III: Methodology, Systems, Applications; Proceedings of the Third International Conference on Artificial Intelligence: Methodology, Systems, Applications (AIMSA '88), Varna, Bulgaria, 1988, pp. 93-102. T. O'Shea and V. Sgurev, editors, North-Holland Press.

We describe a fairly comprehensive handling of the syntax and semantics of comparative constructions. The analysis is largely based on the theory developed by Pinkham, but we advance arguments to support a different handling of phrasal comparatives - in particular, we replace the use of C-ellipsis with a method of interpretation we call contrastive comparison. We explain the reasons for dividing comparative sentences into different categories, and for each category we give an example of the corresponding Montague semantics. The ideas have all been implemented within a large-scale grammar for Swedish, a "toy" version of which is presented, along with examples of the output. This report is a revised and extended version of two earlier papers: (1) "Comparatives in Logic Grammars-Two Viewpoints" located in Natural Language Understanding and Logic Programming II: Proceedings of the 2nd Int'l Workshop on Natural Language Understanding and Logic Programming, Vancouver, Canada, 1987, pp. 153-168, V. Dahl and P. Saint-Dizier, editors, North-Holland Press, 1988; and (2) "Parsing and Interpreting Comparatives" located in Proceedings of the 26th Annual Conference of the Ass. for Computational Linguistics (ACL), Buffalo, 1988, published by the ACL, 1988. Original report number R88018.

The paper criticizes arguments recently advanced by Shoham, McDermott and Sandewall, which purport to demonstrate the relevance of non-monotonic logic to the formalization of reasoning about the evolution of mechanical systems in continuous time. The first half of the paper examines the "Extended Prediction Problem" of Shoham and McDermott; reasons are given to support the claim that the "problem" is the product of a mistaken understanding of the the formal basis of Newtonian mechanics, and has no real existence. An example is given showing how, contrary to Shoham and McDermott's arguments, it is possible to formalise reasoning about the evolution of physical systems in continuous time using only classical logic and differential calculus. The second half then reviews Sandewall's non-monotonic logic for almost-continuous systems. Here it is argued that the proposed framework offers only very marginal advantages in compactness of notation, and generally tends to collapse back into classical logic. In summary, I conclude that there is as yet no good reason to believe that non-monotonic logic will be a useful tool in this area. Original report number R98013.

It is shown how ideas adapted from recent work on explanation-based generalization can be used to allow a logic grammar to "learn" useful derived grammar rules by generalizing them from example sentences. The method is presented in the form of a small Prolog meta-interpreter, and its soundness is formally proved. Examples are given showing the application of the generalizer, first to a toy grammar with 40 rules and then to a largish independantly developed system which involves non-trivial syntactic and semantic analysis. Original report number R89014.

Explanation-based learning is a technique which attempts to optimize performance of a rule-based system by adding new rules constructed from generalizations of successfully-solved examples. The paper summarizes previous work showing how this idea can be used in natural language processing, and describes experiments in which the EBL method was applied to the CHAT-80 system of Pereira and Warren. In particular, we address the problem of assuring the utility of learning a rule, since the benefit of a learned rule may not outweigh the increased search time incurred in checking its applicability. We show that this problem can be overcome in the NL domain by indexing acquired rules by their lexical constraints, which in general vastly reduces the number of potentially applicable rules. Such an indexing method was implemented and timing studies were made comparing its access speed to that of normal linear search. The indexing scheme required an average access time of 35 - 40 ms independent of the number of learned rules. The results suggest that the overhead of the indexing scheme is small.