Path: utzoo!mnetor!uunet!husc6!think!ames!ucbcad!ucbvax!smu.CSNET!leff From: leff@smu.CSNET (Laurence Leff) Newsgroups: comp.doc.techreports Subject: tr-input/uklirb Message-ID: <8712091118.AA13299@ucbvax.Berkeley.EDU> Date: 7 Dec 87 14:26:05 GMT Sender: daemon@ucbvax.BERKELEY.EDU Organization: The ARPA Internet Lines: 650 Approved: techreports@smu.csnet This is our latest list of abstracts of SEKI REPORTS and SEKI WORKING PAPERS for both 1986 and 1987. PhD theses can be ordered at a nominal fee of US$ 10, SEKI REPORTS will cost US$ 2, and SEKI WORKING PAPERS (which are mostly written in German) will cost US$ 1.50, unless there is an exchange agreement. There is, however, another way to obtain SRs and SWPs. You can subscribe to all papers published during a year at a price of US$ 60. You will get each SR and SWP immediately after its publication. The fee covers both postage and packing. If you want to subscribe, please write (don't e-mail) and enclose a cheque. The subscription will end after one year unless you explicitly order and pay for another year. If you want to order any publications, please enclose a cheque payable to the university with the appropriate amount either in US$ or its equivalent in your own currency. Cash is welcome, too. Please, send your orders to the following address: Scarlet Noekel Universitaet Kaiserslautern Fachbereich Informatik Postfach 3049 6750 Kaiserslautern West Germany Phone: +49-631-205-2802 UUCP: ...!mcvax!unido!uklirb!scarlet ------------------------------------------------------------------------- SEKI REPORTS 1987 SEKI REPORT SR-87-01 (modified PhD Thesis) Karl-Hans Blaesius Equality Reasoning Based on Graphs ABSTRACT: The theoretical and practical problems of equality rea- soning in Automated Deduction are notorious. A new method is presented to cope with the enormous search that usually arises when equational axioms are present. Starting from an empty graph a production system constructs graphs which represent solutions for simpler problems defined by abstraction. These graphs contain global information and are plans for guiding the search for a proof of the original problem, represented in the final graph. The construction of equality graphs is based on the idea to reduce the differences between two terms by seperating toplevel symbol and subterms of a functional term. The impact of the ex- plicit representation of information contained in the inference system on the control of inferences is discussed in this work and the method is compared to other equality reasoning methods. The basic principle of our method is formalized and soundness and completeness results are given. An implementation of this method confirmed its adequacy for equality reasoning. Such implementa- tions led to the rejection of previous approaches, but conducted the ideas to the development of our final inference system. SEKI REPORT SR-87-02 (PhD Thesis) Walter Olthoff The Connection between Applicative and Procedural Languages in an Integrated Software Development and Verification System ABSTRACT: Professional production of verified software is incon- ceivable without using sophisticated software engineering en- vironments that either support or even enforce the verification of each development step. In modern systems not only several but also principally different languages are offered to a user. In order to solve the problem of verifying the transition from ap- plicative to procedural levels, we present an algebraic specifi- cation language and a programming language in a common formal framework. The denotional semantics of our languages are based on concepts of abstract data type theory. The procedural programming language ModPascal is introduced as an extension of standard Pas- cal by constructs and concepts of algebraic specification languages. We develop an algebraic notion of correct realization that makes use of so-called representation objects which serve as a connection between language levels. A semi-automatical method for the correctness proof is given; reference is made to the In- tegrated Software Development and Verification System in which the practical feasibility of the approach has been demonstrated. SEKI REPORT SR-87-03 Manfred Schmidt-Schauss Unification in Permutative Equational Theories is Undecidable ABSTRACT: An equational theory E is permutative in every valid equation s =E, t the terms s and t have the same symbols with the same number of occurences. The class of permutative equational theories includes associativity and commutativity and hence is important for unification theory, for term rewriting systems modulo equational theories and corresponding completion pro- cedures. It is shown in this research note that there is no algo- rithm that decides E-unifiability of terms for all permutative theories. The proof technique is to provide for every Turing machine M a permutative theory with a confluent term rewriting system such that narrowing on certain terms simulates the Turing machine M. SEKI REPORT SR-87-04 Rolf Socher Boolean Simplification of First Order Formulae ABSTRACT: For a deduction system it is paramount to recognize the equivalence or supsumption of formulae already at an early stage of the search for the group. Since the equality of two formulae is undecidable in general, we consider the syntactic criterion of equality up to a renaming of the bound variables. We give an al- gorithm that decides whether two closed formulae are equivalent in this restricted sense. It will become apparent that this prob- lem is closely related to the graph isomorphism problem. Furthermore an algorithm is given that decides a special form of subsumption for literal sets. The simplification of formulae based on the recognition of equivalence and subsumption is par- ticularly important for formulae that arise in program verifica- tion tasks. SEKI REPORT SR-87-05 (PhD Thesis) Alex Herold Combination of Unification Algorithms in Equational Theories ABSTRACT: Unification in equational theories, i.e., solving equa- tions in varieties, is a basic operation in Artificial Intelli- gence, in Computer Science and in particular in the field of Au- tomated Deduction. A shortcoming of most known unification algo- rithms is that they are usually designed for a restricted set of terms only. A method is presented to combine unification algorithms for spe- cial equational theories (with disjoint sets of function symbols) to overcome this drawback. This method applies to regular and collapse-free equational theories (a theory is regular if all its axioms have the same variables on each side and it is collapse free if it does not contain an axiom of the form x = t, where x is a variable and t is a non-variable term). The basic idea is first to replace certain subterms by constants and then to unify these constant abstractions. In a recursive step the replaced subterms are considered in turn. Provided the constituent theories are finitary (a finite minimal complete set of unifiers always exists) the combination algorithm is shown to be totally correct. The termination proof is based on an idea of Fages' ter- mination proof for Stickel's associative and commutative unifica- tion algorithm. The abstract algorithm is applied to the theory of associativity and commutativity thus extending the algorithm of Livesay and Siekmann to the whole class of first order terms. As a second ex- ample of application the theory of commutativity is discussed. In order to investigate the limitations of the approach above, the theory of idempotence, which is a collapse theory, is studied and a new idempotent unification algorithm for the class of first order terms is presented. SEKI REPORT SR-87-06 (Diploma Thesis) Michael Beetz Specifying Meta-Level Architectures for Rule-Based Systems ABSTRACT: Explicit and declarative representation of control knowledge and well-structured knowledge bases are crucial re- quirements for efficient development and maintanance of rule- based systems. The CATWEAZLE rule interpreter allows knowledge engineers to meet these requirements by partitioning rule bases and specifying meta-level architectures for control. Among others the following problems arise when providing tools for specifyimg meta-level architectures for control: 1. What is a suitable language to specify meta-level architectures for control? 2. How can a general and declarative language for meta-level architectures be efficiently interpreted? The thesis outlines solutions to both research questions provided by the CATWEAZLE rule interpreter: 1. CATWEAZLE provides a small set of concepts based on a separation of control knowledge in control strategies and control tac- tics and a further categorization of control strategies. 2. For rule-based systems it is efficient to extend the RETE algorithm such that control knowledge can be processed, too. SEKI REPORT SR-87-07 Werner Nutt, Pierre Rety and Gert Smolka Basic Narrowing Revisited ABSTRACT: In this paper we study basic narrowing as a method for solving equations in the initial algebra specified by a ground confluent and terminating term rewriting system. Since we are in- terested in equation solving, we don't study basic narrowing as a reduction relation on terms but consider immediately its reformu- lation as an equation solving rule. This reformulation leads to a technically simpler presentation and reveals that the essence of basic narrowing can be captured without recourse to term unifica- tion. We present an equation solving calculus that features three classes of rules. Resolution rules, whose application is don't care nondeterministic, are the basic rules and suffice for a complete solution procedure. Failure rules detect inconsistent parts of the search space. Simplification rules, whose applica- tion is don't care nondeterministic, enhance the power of the failure rules and reduce the number of necessary don't know steps. Three of the presented simplification rules are new. The rewriting rule allows for don't care nondeterministic rewriting and thus yields a marriage of basic and normalizing narrowing. The safe blocking rule is specific to basic narrowing and is par- ticulary useful in conjunction with the rewriting rule. Finally, the unfolding rule allows for a variety of search strategies that reduce the number of don't know alternatives that need to be ex- plored. Keywords: Equation solving, Universal Unification, Nar- rowing, Basic Narrowing, Normalizing, Narrowing, Rewriting. Acknowledgements: Nutt and Smolka are funded by the Bun- desminister fr Forschung und Technologie under grant ITR8501A. SEKI REPORT SR-87-08 Hans-Juergen Buerckert Matching - A Special Case of Unification? ABSTRACT: Usually matching is considered as a special form of un- ification. Hence most research in unification theory does not take care of the problems arising with matching. After a discus- sion of the various definitions of matching in the literature we compare matching and unification in the more general framework of restricted unification. Restricted unification is unification of terms where not all variables are allowed for substitution and of course matching and unification are special cases of restricted unification. We give certain results in similar behaviour of matching and unification with respect to the existence and the cardinali- ties of minimal and complete solution sets (unification and matching hierarchy) in so called collapse free equational theories, and we show under which conditions this can be general- ized to arbitrary theories. We also present counterexamples where matching and unification behave differently, especially we present an equational theory, in which unification is decidable, matching, however, is undecidable. Matching and restricted unification as defined here is equivalent to extend the given signature with free constants, hence our results can also be interpreted as combination results of combining unification in a given theory with unification in the theory of free constants. Our counterexamples demonstrate that this is not a trivial combination problem, since for example unification might become undecidable under this extension. The solution of this special combination problem is a first step to the more general case of combining unification of a given collaps theory with unification of free functions. Key Words: equational theory, unification, matching, res- tricted unification, collapse free theory, unification hierarchy, combination of equational theories for unification. SEKI REPORT SR-87-09 Michael Lessel, Harold Boley 5-UNIXPERT: Diagnosis of Printer Problems ABSTRACT: The 5-UNIXPERT systems perform knowledge-based diag- nosis in the domain of printers as part of the computer peri- phery. They are implemented in LISPLOG, a functional/logical language that provided the required programming spectrum ranging from operating-system calls to the explenation component. SEKI REPORT SR-87-10 Rolf Socher Graph Isomorphism: Some Special Cases ABSTRACT: This paper investigates some special cases of graphs with a small number of vertices or edges where a characteristic property of the vertices and edges already determines the graph up to isomorphism. We also present counterexamples that show the limits of this approach to the graph isomorphism problem. The main interest in graph isomorphism for automated deduction lies in the fact that the problem of deciding whether a clause is a variant of another clause is a generalization of the graph iso- morphism problem. SEKI REPORT SR-87-11 Gert Smolka TEL (Version 0.9) - Report and User Manual ABSTRACT: TEL is a second generation logic programming language integrating types and functions with relational programming la Prolog. Relations are defined as in Prolog and are executed by typed resolution and backtracking. Functions are defined with conditional equations and are executed by typed innermost rewrit- ing. The most innovative aspect of TEL is its type system, which accomodates parametric polymorphism as in ML and subtypes as in OBJ2. Variables need not be declared since TEL's type checker infers their most general types automatically. Types are present at runtime through typed matching and unification: values are tested for membership in subtypes and variables are con- strained to subtypes. TEL is not a toy language. Almost the entire TEL system has been written in TEL. TEL has a module facility supporting the incremental construction of large programs. Furthermore, TEL sup- ports type-safe file handling and other extra-logical manipula- tions. Acknowledgements: This research was funded by the Bun- desministerium fr Forschung und Technologie under grant ITR8501A. Version 0.9 of TEL is being implemented by Costa Mossiadis, Werner Nutt, Reinhard Praeger, and Georg Seul. The first version of TEL was implemented by Michael Schmitt. SEKI REPORT SR-87-12 Michael A. McRobbie Towards Efficient Knowledge-Based Automated Theorem Proving for Non-Standard Logics ABSTRACT: Researchers in artificial intelligence and computer science have recently begun to take an interest in logics studied by logicians and philosophers, in some cases for millennia. These are logics such as deontic, epistemic, intuitionistic, modal, paraconsistent, relevent and temporal logics, all of which are usually collectively called non-standard logics. Given the nature of much of this interest, many of these researchers have correctly pointed to the importance of efficient automated theorem proving systems for these logics. However very little work has actually been done on implementing such systems. Where such systems have been implemented, they have usually not been able to prove anything other than elementary theorems of these logic. In this paper we discuss a technique for greatly increas- ing the efficiency of automated theorem provers for these logics. In short this technique takes advantage of the fact that while most important non-standard logics do not have finite charac- teristic models, (in the sense that thruth tables are a finite charac- teristic model for classical propositional logic), they do have finite models. These models invalidate all the theorems of a given logic and some non-theorems. They invalidate the rest of the non-theorems. Hence this technique involves using the models to direct a search by an automated theorem prover for a proof by filtering out or pruning the items of the search space which the models invalidate. Consequently we call this technique the model pruning technique. This technique does rely on the underlying proof method of the automated theorem prover having certain characteristics, but provided it does, this technique has almost universal applicability. Key Phrases: Automated Theorem Proving, Non-Standard Log- ics, Non-Classical Logics, Many-Valued Logics, Knowledge-Based Search Models. Computing Reviews Classification: F.4.1, I.2.3, I.2.8. SEKI REPORT SR-87-13 Rolf Socher Optimized Transformation Between Conjunctive and Disjunctive Nor- mal Forms ABSTRACT: Resolution based theorem proving systems require the conversion of predicate logic formulae into clausal normal form. One step of all procedures performing this transformation is the multiplication into conjunctive normal form. In general this is a critical step, since it can cause an inflation of the original formula. In many cases the clausal normal form that is obtained even contains a lot of redundant clauses. This paper presents a multiplication algorithm that avoids the generation of many of these redundant clauses. It is shown that the set of clauses gen- erated by this algorithm is the set of prime implicants of the original formula. Especially in those cases where the usual muli- plication algorithm produces a contradictory set of ground clauses the improved algorithm generates the empty clause. SEKI REPORT SR-87-14 Gert Smolka et al. Order-Sorted Equational Computation ABSTRACT: The expressive power of many-sorted equational logic can be greatly enhanced by allowing for supports and multiple function declarations. In this paper we study some compu- tation- al aspects of such a logic. We start with a self-contained intro- duction to order-sorted equational logic including initial alge- bra semantics and deduction rules. We then present a theory of order-sorted term rewriting and show that the key results for un- sorted rewriting extend to sort decreasing rewriting. We continue with a review of order-sorted unification and prove the basic results. In the second part of the paper we study hierarchical order sorted specifications with strict partial functions. We de- fine the appropriate homomorphisms for strict algebras and show that every strict algebra is isomorphic to a strict algebra with at most one error element. For strict specifications, we show that their categories of strict algebras have initial objects. We validate our approach to partial functions by proving that com- pletely defined total functions can be defined as partial without changing the initial algebra semantics. Finally, we provide de- cidable sufficient criteria for the consistency and strictness of ground confluent rewriting systems. Keywords: Order-Sorted Equational Logic, Algebraic Specifications, Initial Algebra Semantics, Partial Functions, Rewriting, Unification, Subsorts, Inheritance, Logic Programming. Acknowledgements: We are grateful to Hans-Juergen Buerck- ert, Manfred Schmidt- Schauss and Joerg Siekmann for many discus- sions. The research reported in this paper has been supported in part by the Bundesminister fuer Forschung und Technologie, con- tract ITR8501A, the office of Naval Research, contracts N00014- 82-C-0333, N00014-85-C-0417 and N00014-86-C-0450, and a gift from the system Development Foundation. SEKI WORKING PAPERS 1987 SEKI WORKING PAPER SWP-87-01 (in German) Ansgar Bernardi, Michael Dahmen, Manfred Meyer LISPLOG Benutzerhandbuch ABSTRACT: This paper is intended to serve as a user's manual for LISPLOG. It gives a short description of the syntax of LISPLOG to- gether with an explanation of all commands available on the top- level of LISPLOG. The concepts and the commands of the LISPLOG tracer/breaker are also described. This manual should give you the ability to use the LISP- LOG system. It doesn't explain the concepts of the LISP/PROLOG integration or its implementation details. SEKI WORKING PAPER SWP-87-02 (in German) Manfred A. Meyer Entwurf und Implementierung einer Interaktionsumgebung fr LISPLOG ABSTRACT: This paper deals with the design and implementation of an interactive programming environment for an integration of LISP and PROLOG called LISPLOG, which is currently developed at the university of Kaiserslautern. This programming environment consists of a box model tracer with backtrace possibility and a very comfortable break- package. Two innovative interactive tools for non-deterministic languages that have been explored in LISPLOG are a 'cut indica- tor' and a 'manual cutter'. In addition, an extension of the box model for the func- tional part of LISPLOG is discussed and prototypically implement- ed. Finally, several improvements of the user interface are roughly outlined, and the current implementation is critically reviewed once again. SEKI WORKING PAPER SWP-87-03 Harold Boley Fone and Fall: Forward-with-Backward Chaining in LISPLOG ABSTRACT: A small extension for incorporating forward chaining into and on top of LISPLOG's backward chaining framework is presented. SEKI WORKING PAPER SWP-87-04 Harold Boley Goal: Backward-with-Forward Chaining in LISPLOG ABSTRACT: A tiny extension for performing forward chaining to prove goals set up by LISPLOG's backward-chaining mechanism is introduced. SEKI WORKING PAPER SWP-87-05 (in German) Volker Penner Implementation logischer Sprachen auf Multiprozessor-Systemen ABSTRACT: The main contribution of this paper consists in a pro- posal for implementing parallel logical languages on distributed systems using - a parallel extension (PWAM) of Warren's abstract machine (WAM) in order to take advantage of approved techniques, - an approach for modularizing logical programs in order to meet restricted resources, and - integrating committed choice nondeterminism in order to allow backtrack-free implementations. The text is devided as follows: first we give an overview over the main notions playing a dominent role in parallel languages, then we introduce the basic process-oriented semantics and dis- cuss the way "or"-parallelism is handled. Starting point of the last chapters is a brief description of the WAM, which is fol- lowed by a discussion of the static structure and dynamic behavior of it's parallel counterpart (PAM) stressing essentially the basic ideas and omitting technical details. SEKI WORKING PAPER SWP-87-06 (in German) Michael Dahmen Modules and Streams in Lisplog ABSTRACT: This paper discusses two extensions of the LISPLOG sys- tem, called modules and streams. The module system enables the LISPLOG user to build his program from a number of seperate databases (modules). The interaction between the modules is defined by special interfaces. The result is a hierarchical structure of the LISPLOG database. The second part describes an extension of the LISP-LISPLOG inter- face for delayed computation of the solutions of a LISPLOG in- quiry. Therefore it becomes possible to compute any number of solutions without specifying that number before the computation starts. Even an infinite number of solutions may be intensional represented by means of a stream. SEKI WORKING PAPER SWP-87-08 Klaus Noekel Conceptual Dependency Theory: ein Ueberblick (in German) ABSTRACT: The paper reflects the contents of a talk given at the 2nd KL-AI-Workshop. Its main concern is the knowledge representa- tion formalism of CD theory. We begin with an introduction to the syntax and semantics of CD structures. Next, we explain how CD structures can be put to use in the representation of the meaning contents of utterances. Primitive ACTs play an important aspect in the transition from the input text to CD structures and lead to a general discussion of the principle of CD theory that mean- ing should be represented using a small (minimal?) number of primitives. The exposition af the static aspects of CD structures is complemented by a brief look at conceptual inference rules and the way that CD theory was actually used in SchankTs programs MARGIE and SAM. We close with a summary of critical statements made by both Schank and other researchers in the field. Pointers to the literature are provided. Key Words: natural language processing, knowledge representation, semantic nets.