Techniques for efficiently evaluating future time Linear Temporal Logic (abbreviated LTL) formulae on finite execution traces are presented. While the standard models of LTL are infinite traces, finite traces appear naturally when testing and/or monitoring real applications that only run for limited time periods. A finite trace variant of LTL is formally defined, together with an immediate executable semantics which turns out to be quite inefficient if used directly, via rewriting, as a monitoring procedure. Then three algorithms are investigated. First, a simple synthesis algorithm for monitors based on dynamic programming is presented; despite the e#- ciency of the generated monitors, they unfortunately need to analyze the trace backwards, thus making them unusable in most practical situations. To circumvent this problem, two rewritingbased practical algorithms are further investigated, one using rewriting directly as a means for online monitoring, and the other using rewriting to generate automata-like monitors, called binary transition tree finite state machines (and abbreviated BTT-FSMs). Both rewriting algorithms are implemented in Maude, an executable specification language based on a very e#cient implementation of term rewriting. The first rewriting algorithm essentially consists of a set of equations establishing an executable semantics of LTL, using a simple formula transforming approach. This algorithm is further improved to build automata on-the-fly via caching and reuse of rewrites (called memoization), resulting in a very e#cient and small Maude program that can be used to monitor program executions. The second rewriting algorithm builds on the first one and synthesizes provably minimal BTT-FSMs from LTL formulae, which can then be used to a...

Issues of representation arise in natural language processing, user interface design, art, and indeed, communication with any medium. This paper addresses such issues using algebraic semiotics, which draws on algebraic speci cation to give (among other things) an algebraic theory of representation, and a generalization of blending in the sense of cognitive linguistics.

Circular coinduction is a technique for behavioral reasoning that extends cobasis coinduction to specifications with circularities. Because behavioral satisfaction is not recursively enumerable, no algorithm can work for every behavioral statement. However, algorithms using circular coinduction can prove every practical behavioral result that we know. This paper proves the correctness of circular coinduction and some consequences.

recent advances in web technology, interface design, and specification. Our effort to improve the usability of such systems has led us into algebraic semiotics, while our effort to develop better formal methods for distributed concurrent systems has led us into hidden algebra and fuzzy logic. This paper discusses the Tatami system design, especially its software architecture, and its user interface principles. New work in the latter area includes an extension of algebraic semiotics to dynamic multimedia interfaces, and integrating Gibsonian affordances with algebraic semiotics. 1

This work describes the formal semantics of SCHEME 1 as an equational theory in the MAUDE rewriting system. The semantics is based on continuations and is highly modular. We briefly investigate the relationship between our methodology for defining programming languages and other semantic formalisms. We conclude by showing some performance results of the interpreter obtained for free from the executable specification.

The Tatami project is building a system to support software engineering over the internet, exploiting recent advances in web technology, interface design, and specification. Our effort to improve the usability of such systems led us into algebraic semiotics, while our effort to develop better formal methods for distributed concurrent systems led us into hidden algebra. We discuss the Tatami system design, especially user interface issues, and sketch an extension of algebraic semiotics for interface dynamics. 1 Introduction The Tatami project has pursued three main goals: 1. explore novel multimedia interface design principles, for easing the use of complex interactive systems; 2. build and use a generic distributed environment for cooperative work; and 3. verify distributed concurrent software. We discuss these goals in turn. The first is motivated by the difficulties many practicing engineers have with formal methods tools. We have taken theorem provers as a typically difficult c...

We present a rewriting-based algorithm for efficiently evaluating future time Linear Temporal Logic (LTL) formulae on finite execution traces online. While the standard models of LTL are infinite traces, finite traces appear naturally when testing and/or monitoring real applications that only run for limited time periods. The presented algorithm is implemented in the Maude executable specification language and essentially consists of a set of equations establishing an executable semantics of LTL using a simple formula transforming approach. The algorithm is further improved to build automata on-the-fly from formulae, using memoization. The result is a very efficient and small Maude program that can be used to monitor program executions. We furthermore present an alternative algorithm for synthesizing provably minimal observer finite state machines (or automata) from LTL formulae, which can be used to analyze execution traces without the need for a rewriting system, and can hence be used by observers written in conventional programming languages. The presented work is part of an ambitious runtime verification and monitoring project at NASA Ames, called PATHEXPLORER, and demonstrates that rewriting can be a tractable and attractive means for experimenting and implementing program monitoring logics. 1

Introduction Agents are increasingly upon us. Although opposition is rare, \intelligent agents" have been attacked for user interface problems, and on larger social issues. Agent supporters have countered these arguments and raised doubts about alternative technologies. We place this in historical, social, and ethical contexts, noting the cyclic nature of such debates. One conclusion is that many problems with arti cial agents arise from a poor understanding of social aspects of human agents. 2. Historical Perspectives The history of technology has seen many movements call for human-like systems, and use anthropomorphic terminology to generate understanding and support. Such movements often make excessive claims, perhaps misled by their own rhetoric or their (sometimes impressive) partial success. This raises unrealistic expectations, which often leads to disappointment, which is surprisingly often followed by rebirth with similar goals, and somewhat improved terminology and techno