José F. Quesada

Maude: specification and programming in rewriting logic

Maude is a high-level language and a high-performance system supporting executable specification and declarative programming in rewriting logic. Since rewriting logic contains equational logic, Maude also supports equational specification and programming in its sublanguage of functional modules and theories. The underlying equational logic chosen for Maude is membership equational logic, that has sorts, subsorts, operator overloading, and partiality definable by membership and equality conditions. Rewriting logic is reflective, in the sense of being able to express its own metalevel at the object level. Reflection is systematically exploited in Maude endowing the language with powerful metaprogramming capabilities, including both user-definable module operations and declarative strategies to guide the deduction process. This paper explains and illustrates with examples the main concepts of Maudes language design, including its underlying logic, functional, system and object-oriented modules, as well as parameterized modules, theories, and views. We also explain how Maude supports reflection, metaprogramming and internal strategies. The paper outlines the principles underlying the Maude system implementation, including its semicompilation techniques. We conclude with some remarks about applications, work on a formal environment for Maude, and a mobile language extension of Maude.

The Maude System

Maude is a high-performance language and system supporting both equational and rewriting logic computation for a wide range of applications, including development of theorem proving tools, language prototyping, executable specification and analysis of concurrent and distributed systems, and logical framework applications in which other logics are represented, translated, and executed. Maude’s functional modules are theories in membership equational logic [8,1], a Horn logic whose atomic sentences are either equalities t = t′ or membership assertions of the form t : s, stating that a term t has a certain sort s. Such a logic extends OBJ3’s [4] order-sorted equational logic and supports sorts, subsorts, subsort polymorphic overloading of operators, and definition of partial functions with equationally defined domains. Maude’s functional modules are assumed to be Church-Rosser; they are executed by the Maude engine according to the rewriting techniques and operational semantics developed in [1]. Membership equational logic is a sublogic of rewriting logic [6]. A rewrite theory is a pair (T, R) with T a membership equational theory, and R a collection of labeled and possibly conditional rewrite rules involving terms in the signature of T . Maude’s system modules are rewrite theories in exactly this sense. The rewrite rules r : t −→ t′ in R are not equations. Computationally, they are interpreted as local transition rules in a possibly concurrent system. Logically, they are interpreted as inference rules in a logical system. This makes rewriting logic both a general semantic framework to specify concurrent systems and languages [7], and a general logical framework to represent and execute different logics [5]. Rewriting in (T, R) happens modulo the equational axioms in T . Maude supports rewriting modulo different combinations of associativity, commutativity, identity, and idempotency axioms. The rules in R need not be Church-Rosser and need not be terminating. Many different rewriting paths are then possible; therefore, the choice of appropriate strategies is crucial for executing rewrite theories. In Maude, such strategies are not an extra-logical part of the language.

Maude as a Metalanguage

Abstract One of the key goals of rewriting logic from its beginning has been to provide a semantic and logical framework in which many models of computation and languages can be naturally represented. There is by now very extensive evidence supporting the claim that rewriting logic is indeed a very flexible and simple logical and semantic framework. From a language design point of view the obvious question to ask is: how can a rewriting logic language best support logical and semantic framework applications, so that it becomes a metalanguage in which a very wide variety of logics and languages can be both semantically defined, and implemented? Our answer is: by being reflective. This paper discusses our latest language design and implementation work on Maude as a reflective metalanguage in which entire environments---including syntax definition, parsing, pretty printing, execution, and input/output---can be defined for a language or logic £ of choice.

New technique to enhance the performance of spoken dialogue systems by means of implicit recovery of ASR errors

This paper proposes a new technique to implicitly correct some ASR errors made by spoken dialogue systems, which is implemented at two levels: statistical and linguistic. The goal of the former level is to employ for the correction knowledge extracted from the analysis of a training corpus comprised of utterances and their corresponding ASR results. The outcome of the analysis is a set of syntactic-semantic models and a set of lexical models, which are optimally selected during the correction. The goal of the correction at the linguistic level is to repair errors not detected during the statistical level which affects the semantics of the sentences. Experiments carried out with a previouslydeveloped spoken dialogue system for the fast food domain indicate that the technique allows enhancing word accuracy, spoken language understanding and task completion by 8.5%, 16.54% and 44.17% absolute, respectively.

Towards Maude 2.0

Abstract Maude 2.0 is the new version of the Maude rewriting logic language currently under development. Maude 2.0s three main goals are: (i) greater generality and expressiveness; (ii) efficient support for a wider range of programming applications; and (iii) usability as a key component for developing internet programming and mobile computing systems. To meet these goals, a number of new features have been added. The membership equational logic of functional modules and the rewriting logic of system modules are now supported in their greatest possible generality, and the operational semantics of object-oriented modules guarantees object and message fairness. Module operations in Full Maude are also more general thanks to parameterized theories and views. Efficient support for a wider range of programming applications is provided both by the Maude compiler—which can reach up to 15 million rewrites per second on a 667MHz Xeon—and by a library of new built-in modules. Besides new built-in functional modules, a key new feature is built-in object-oriented modules that provide flexible interaction with external objects such as file systems, window systems, and internet sockets. In particular, built-in internet sockets will provide excellent support for a new declarative style of internet programming in Maude, and will be used as a key building block to implement the Mobile Maude language.

Future and Emerging Trends in Language Technology. Machine Learning and Big Data

Despite its relatively short period of existence as a scientific area, natural language processing has gone through a succession of diverse mainstream research paradigms. How similar are these inflection moments in the history of the research on language technology? What can we learn from that similarity, if any, about the overall shape of the evolution of this field? And importantly, what can we anticipate from this shape, if any, about the future and emerging trends in language technology? — which is the topic of the workshop where this paper was presented. The result of this study is meant to be of help to organize research agendas of centers, laboratories and individual researchers and innovators, as well as to guide informed institutional funding and support for research and innovation in language technology.

Future and Emergent Trends in Language Technology

In most cases, speech and language technology is used for explicit interaction with computers. However, in a connected world the technology can also to be used for other purposes. It is the aim of this position statement to open research questions which point at the potential of speech and language technology for enabling new interaction experiences such as implicit interactions, body sensors, adaptive and persuasive interfaces. The research questions are grouped into three domains: user, system and context. In the user domain, our focus will be on information that can be extracted from the user. In the system domain, our focus in on crowdsourcing and privacy concerns. The focus point in the context domain is on implicit interactions and intelligent interactions.

New Technique for Handling ASR Errors at the Semantic Level in Spoken Dialogue Systems

This paper proposes a new technique to develop more robust spoken dialogue systems, which aims to repair incorrect semantic representations obtained by the systems due to ASR errors. To do so, it relies on a training stage that takes into account previous system misunderstandings for each dialogue state. Experiments have been carried out employing two systems (Saplen and Viajero) previously developed in our lab, which employ a prompt-independent language model and several prompt-dependent language models for ASR. The results, obtained for a corpus of 20,000 simulated dialogues, show that the technique enhances system performance for both kinds of language model, especially for the prompt-independent language model.

Lexical Object Theory: Specification Level

Unification has become a major paradigm in Mathematical and Computational Linguistics. The research done in this area may be classified in four main streams: feature structures as an adequate model for the description of linguistic phenomena, typed unification, representation of feature structures, and unification algorithms. This work proposes a new approach to unification-based Mathematical and Computational Linguistics: the Lexical Object Theory. The main design criteria are based on linguistic motivation, computational efficiency and formal soundness. The first part of the work outlines the main characteristics of the Lexical Object Theory, its comprehensive orientation, and its layered structure based on the separation of the following levels: specification, transformation, typification, representation and unification. The second part concentrates on the specification level of the Lexical Object Theory. The linguistic motivation of this model is presented, as well as a detailed description of the specification formalism, the computational model it is based on, and finally, the inference rules on lexical objects at the specification level.