CoCasl at Work — Modelling Process Algebra

CoCasl[11], a recently developed coalgebraic extension of the algebraic specification language Casl[2], allows for modelling systems in terms of inductive datatypes as well as of co-inductive process types. Here, we demonstrate how to specify process algebras, namely CCS[10] and CSP[8,17], within such an algebraic-coalgebraic framework. It turns out that CoCasl can deal with the fundamental concepts of process algebra in a natural way: The type system of communications, the syntax of processes and their structural operational semantics fit well in the algebraic world of Casl, while the additional coalgebraic constructs of CoCasl cover the various process equivalences (bisimulation, weak bisimulation, observational congruence, and trace equivalence) and provide fully abstract semantic domains. CoCasl hence becomes a meta-framework for studying the semantics and proof theory of reactive systems.     

Necessary and sufficient conditions for robust identification of uncertain LTI systems

Robust identification of uncertain systems arises whenever a chosen family of models does not completely describe reality. In these situations the issue of unmodeled dynamics gains significance in addition to random measurement noise. To deal with such mixed stochastic/deterministic settings we introduce a novel notion for robust consistency, which requires that the expectation (with respect to noise) of the worst-case (with respect to unmodeled dynamics) identification error asymptotically approach zero. It turns out that this notion leads to transparent necessary and sufficient conditions. We show that robust consistency holds, if and only if there is an instrument-input-pair capable of annihilating the residual error as well as stochastic noise. An extension of this result to the well-known “bounded but unknown” noise model shows that if we were to remove a set of Lebesgue measure zero, the error bound asymptotically approaches zero.     

DWAM — A WAM model extension for disjunctive logic programming

Answering queries in disjunctive logic programming requires the use of ancestry-resolution. The resulting complication makes it difficult to implement a Prolog-type query answering procedure for disjunctive logic programs. However, SLO-resolution provides a mechanism which is similar to SLD-resolution and hence offers a solution to this problem. The Warren Abstract Machine has been a very effective model for implementing Prolog. In this paper, we extend the WAM model of Prolog and adapt it for DISLOG — a language for disjunctive logic programming. We describe the extensions and additional instructions needed to make WAM viable for modeling and executing DISLOG. The extension is made in such a way that the original architecture is not disturbed and a Prolog program will execute as efficiently as it does in the original WAM.This work was done while the author was at the University of Kentucky.     

Global stabilizability of homogeneous vector fields of odd degree

In this paper we deal with global stabilizability at the origin of a homogeneous vector field by means of homogeneous feedbacks of the same degree. We give a sufficient condition, which turns out to be also necessary in the linear case. For a particular class of systems, this condition is implied by a local controllability assumption.     

Denotational and operational semantics for prolog

The semantics of PROLOG programs is usually given in terms of the model theory of first-order logic. However, this does not adequately characterizethe computational behavior of PROLOG programs. PROLOG implementations typically use a sequential evaluation strategy based on the textual order of clauses and literals in a program, as well as nonlogical features like cut. In this work we develop a denotational semantics that captures thecomputational behavior of PROLOG. We present a semantics for “cut-free” PROLOG, which is then extended to PROLOG with cut. For each case we develop a congruence proof that relates the semantics to a standard operational interpreter. As an application of our denotational semantics, we show the correctness of some standard “folk” theorems regarding transformations on PROLOG programs.     

Techniques of integrating Datalog with PROLOG

Since extending DATALOG to a general-purpose programming language seems very difficult,many projects have embedded a DATALOG-based query laguage into a procedural host language,such as CORAL,Glue-Nail,etc.Although DATALOG can be consideed as function-free PROLOG,they are very different in many aspects.For instance,DATALOG is declarative while PROLOG isn‘t,DATALOG takes “a-set-at-a-time” mode of evaluation but PROLOG takes “a-tuple-at-a-time”one,DATALOG is only a query language whereas PROLOG is a general-purpose programming language.It is thought that integrating DATALOG with PROLOG may take their advantages.KBASEP is such a language.It uses KBASE as the query language and PROLOG as its procedural host language,where KBASE is a ne extemsion of DATALOG with negation and function.This paper introduces the integration techniques used in KBASE-P system.     

Pi+演算及其对Petri网的表达

为了研究Pi演算模型的表达能力,作者用它来表达Petri网系统,证明了Petri网的某些子类,如自由选择网等,可以直接用Pi演算表达.然而对于一般的Petri网,表达却遇到了困难.文中提出了一种对Pi演算的扩展,称为Pi+演算,在原有Pi演算的通信机制中增加了多原语同步通信机制.证明了所有一般Petri网系统均可以用P...     

The transparent PROLOG machine (TPM): an execution model and graphical debugger for logic programming

An augmented and⧸or tree representation of logic programs is presented as the basis for an advanced graphical tracing and debugging facility for PROLOG. An extension of our earlier work on “retrospective zooming”, this representation offers several distinct advantages over existing tracing and debugging facilities: (1) it naturally incorporates traditional and⧸or trees and Byrd box models (call⧸exit⧸fail⧸redo procedural models) as special cases; (2) it can be run in slow-motion, close-up mode for novices or high-speed, long-distance mode for experts with no attendant conceptual change; (3) it serves as the uniform basis for textbook material, video-based teaching material, and an advanced user interface for experienced PROLOG programmers; (4) it tells the truth about clause head matching and deals correctly with the cut. One of the key insights underlying the work is the realization that it is possible to display an execution space of several thousand nodes in a meaningful way on a modern graphics workstation. By enhancing and⧸or trees to include “status boxes” rather than simple “nodes”, it is possible to display both a long-distance view of execution and the full details of clause-head matching. Graphical “collapsing” techniques enable the model to deal with user-defined abstractions, higher-order predicates such as setof, and definite-clause grammars. The current implementation runs on modern graphics workstations and is written in PROLOG.     

Probability logic and optimization SAT: The PSAT and CPA models

Both probabilistic satisfiability (PSAT) and the check of coherence of probability assessment (CPA) can be considered as probabilistic counterparts of the classical propositional satisfiability problem (SAT). Actually, CPA turns out to be a particular case of PSAT; in this paper, we compare the computational complexity of these two problems for some classes of instances. First, we point out the relations between these probabilistic problems and two well known optimization counterparts of SAT, namely Max SAT and Min SAT. We then prove that Max SAT with unrestricted weights is NP-hard for the class of graph formulas, where Min SAT can be solved in polynomial time. In light of the aforementioned relations, we conclude that PSAT is NP-complete for ideal formulas, where CPA can be solved in linear time.     

The occur-check problem revisited

A method is presented for executing PROLOG programs which avoids almost all unnecessary occur-checks. The method is based on a dynamic classification of the context in which logical variables occur. No static global analysis of the PROLOG program is required to detect the places where an occur-check has to be made. The presented method has also an important side benefit. It considerably cuts down on the number of memory references during the execution of PROLOG programs. Furthermore, in most cases it avoids “trailing” and “untrailing” of unbound variables altogether. Due to this fact the employed method actually speeds up PROLOG execution. The method is discussed in terms of an actual implementation based on the Warren abstract PROLOG instruction set. However, the method should be applicable to other implementation models as well. No assumptions are made with respect to particular hardware.     

Decidable call-by-need computations in term rewriting

The theorem of Huet and Lévy stating that for orthogonal rewrite systems (i) every reducible term contains a needed redex and (ii) repeated contraction of needed redexes results in a normal form if the term under consideration has a normal form, forms the basis of all results on optimal normalizing strategies for orthogonal rewrite systems. However, needed redexes are not computable in general. In the paper we show how the use of approximations and elementary tree automata techniques allows one to obtain decidable conditions in a simple and elegant way. Surprisingly, by avoiding complicated concepts like index and sequentiality we are able to cover much larger classes of rewrite systems. We also study modularity aspects of the classes in our hierarchy. It turns out that none of the classes is preserved under signature extension. By imposing various conditions we recover the preservation under signature extension. By imposing some more conditions we are able to strengthen the signature extension results to modularity for disjoint and constructor-sharing combinations.     

一种基于PROLOG的ES建造工具库的研究与实现

本文描述了一基于ＰＲＯＬＯＧ的专家系统建造工具库ＰＴＥＳ的实验系统。ＰＴＥＳ是用ＰＲＯＬＯＧ编写的，该系统根据支持基于规则的知识表示及近似推理对ＰＲＯＬＯＧ的知识处理能力进行了扩充。ＰＴＥＳ的推理机制使用了可能性逻辑及模糊集合理论作为其逻辑基础并以一种形式化的方法提供了处理非确定事实及非确定规则的能力。     

Expression of syntactic and semantic features in logic-based grammars

In this paper, we introduce and initiate a formalism to represent syntactic and semantic features in logic-based grammars. We also introduce technical devices to express feature-checking and feature-inheritance mechanisms. This leads us to propose some extensions to the basic unification mechanism of PROLOG. Finally, we consider the problem of long-distance dependency relations between constituents in gapping grammars rules from the point of view of morphosyntactic features that may change depending on the position occupied by the moved constituents. What we propose is not a new linguistic theory about features, but rather a formalism and a set of tools that we think will be useful to grammar writers to describe features and their relations in grammar rules.     

Probability logic and optimization SAT: The PSAT and CPA models

Both probabilistic satisfiability (PSAT) and the check of coherence of probability assessment (CPA) can be considered as probabilistic counterparts of the classical propositional satisfiability problem (SAT). Actually, CPA turns out to be a particular case of PSAT; in this paper, we compare the computational complexity of these two problems for some classes of instances. First, we point out the relations between these probabilistic problems and two well known optimization counterparts of SAT, namely Max SAT and Min SAT. We then prove that Max SAT with unrestricted weights is NP-hard for the class of graph formulas, where Min SAT can be solved in polynomial time. In light of the aforementioned relations, we conclude that PSAT is NP-complete for ideal formulas, where CPA can be solved in linear time.     

Discovering rules to design newspapers: An inductive constraint logic programming approach

Inductive logic programming combines both machine learning and logic programming techniques. ILP uses first-order predicate logic restricted to Horn clauses as an underlying language. Thus, programs induced by an ILP system inherit the classical limitations of PROLOG programs. Constraint logic programming avoids some of the limitations of logic programming, and so ILP aims to induce programs that employ this paradigm. Current ILP systems that induce constrained logic programs extend systems based on the normal semantics ofILP. In this article we introduce IC-Log, a new system that induces constrained logic programs and relies on an extension ofa nonmonotonic semantics-based system. We then present an application of IC-Log in the field ofcomputer-aided publishing.     

Control of mechanical systems on Lie groups based on vertically transverse functions

The transverse function approach to control provides a unified setting to deal with practical stabilization and tracking of arbitrary trajectories for controllable driftless systems. Controllers derived from that approach offer advantages over those based on more classical techniques for control of nonholonomic systems. Nevertheless, its extension to more general classes, such as critical underactuated mechanical systems, is not immediate. The present paper explores a possible extension by developing a framework that allows one to cast point stabilization problems for (left-invariant) second-order systems on Lie groups, including simple mechanical systems. The approach is based on “vertical transversality,” a property exhibited by derivatives of transverse functions. In this paper, we lay out the theoretical foundations of our approach and present an example to illustrate some of its features. This work was partially funded by CONACYT under grants No. 66910 and 52914.     

Analysis and efficient implementation of a linguistic fuzzy c-means

The paper is concerned with a linguistic fuzzy c-means (FCM) algorithm with vectors of fuzzy numbers as inputs. This algorithm is based on the extension principle and the decomposition theorem. It turns out that using the extension principle to extend the capability of the standard membership update equation to deal with a linguistic vector has a huge computational complexity. In order to cope with this problem, an efficient method based on fuzzy arithmetic and optimization has been developed and analyzed. We also carefully examine and prove that the algorithm behaves in a way similar to the FCM in the degenerate linguistic case. Synthetic data sets and the iris data set have been used to illustrate the behavior of this linguistic version of the FCM.     

System structure for parallel logic programming

A system structure supporting parallel processing in general and parallel logic programming and expert system applications in particular is described. It is not based on special hardware but has rather been designed as an evolutionary extension to most existing machine architectures. It is aimed at parallel processing support for e.g. PROLOG as well as for expert system (shells) implemented in a general purpose language. A layered structure consisting of an extended machine interface and a macro language is chosen to support a range of various applications.     

Strong stabilisation and decay estimate for unbounded bilinear systems

In this article, we deal with distributed bilinear systems, where the operator of control is supposed to be unbounded in the sense that it is bounded from the state space into some extension. Then we give sufficient conditions for strong stabilisation. Also the rate of convergence of the state is estimated. An illustrating example is given.     

MOLOG: A system that extends PROLOG with modal logic

In this paper we present an extension of PROLOG using modal logic. A new deduction method is also given based on a rule closer to the classical inference rule of PROLOG.