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Jose Alferes

Universidade Nova de Lisboa, Departamento de Informática, Faculty Member

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Papers by Jose Alferes

External Transaction Logic : reasoning and executing transactions involving external domains 1

In this work we present External Transaction Logic, a logic that extends Transaction logic with t... more In this work we present External Transaction Logic, a logic that extends Transaction logic with the ability to model and execute transactions requiring interactions with external entities, as e.g. external web-source, web-services or agents. Transactions are defined in a logic programming style by the composition of internal and external primitives. These primitives are incorporated in a quite general manner, as a parameter of the External Transaction Logic theory, allowing the specification of transactions integrating knowledge and actions from multiple sources and semantics. Since one has different control over internal and external domains, different transaction properties are ensured depending on where actions are executed. Namely, internal actions executed in a knowledge base that we fully control, follow the standard ACID model of transactions. Contrarily, transactional properties over actions executed externally need to be relaxed, as it is impossible to rollback actions exec...

Planning as Abductive Updating

In this paper we show how planning can be achieved by means of abduction, a form of non-monotonic... more In this paper we show how planning can be achieved by means of abduction, a form of non-monotonic reasoning, in the LUPS language. LUPS employs the recently introduced notion of Dynamic Logic Programming, whereby the knowledge representation rules, namely those representing actions, can dynamically change, crucial when agents are to be situated in evolving environments. By integrating into a single framework several recent developments in the logic programming and non-monotonic reasoning field of research, this work contributes to a better modeling and understanding of rational agents. At the same time, it enjoys the advantages of a declarative and implementable specification, shortening the usual gap between theory and practice often found in logical based approaches to agents. The system integrating Dynamic Logic Programming, LUPS and Abduction, in order to achieve this form of planning, has been implemented.

Deontic Logic Programs (Extended Abstract)

Deontic logic programming (DLP) is a framework combining deontic logic and non-monotonic logic pr... more Deontic logic programming (DLP) is a framework combining deontic logic and non-monotonic logic programming, and it is useful to represent and reason about normative systems. In this paper we propose an implementation for reasoning in DLP that combines, in a modular way, a reasoner for deontic logic with a reasoner for stable model semantics.

Evolving reactive logic programs

Intelligenza Artificiale, 2011

to strengthening the semantics foundations of dynamic logic programs, we describe a simple formal... more

Modular Logic Programming

Logic programming has often been considered less than adequate for modelling the dynamics of know... more Logic programming has often been considered less than adequate for modelling the dynamics of knowledge changing over time. In this paper we describe a simple though quite powerful approach to modelling the updates of knowledge bases expressed by generalized logic programs, by means of a new language, hereby christened EVOLP (after EVOlving Logic Programs). The approach was first sparked by a critical analysis of previous efforts and results in this direction [1,2,7,11], and aims to provide a simpler, and at once more general, formulation of logic program updating, which runs closer to traditional logic programming (LP) doctrine. From the syntactical point of view, evolving programs are just generalized logic programs (i.e. normal LPs plus default negation also in rule heads), extended with (possibly nested) assertions, whether in heads or bodies of rules. From the semantics viewpoint, a model-theoretic characterization is offered of the possible evolutions of such programs. These evolutions arise both from self (or internal) updating, and from external updating too, originating in the environment. This formulation sets evolving programs on a firm basis in which to express, implement, and reason about dynamic knowledge bases, and opens up a number of interesting research topics that we brush on.

An Evolvable Rule-Based E-mail Agent

Lecture Notes in Computer Science, 2003

The Semantic Web is a "living organism", which combines autonomously evolving data sources/knowle... more The Semantic Web is a "living organism", which combines autonomously evolving data sources/knowledge repositories. This dynamic character of the Semantic Web requires (declarative) languages and mechanisms for specifying its maintenance and evolution. For example, for changing the behaviour of a data source, so that a new rule becomes into effect, one should not be concerned with the complex, interrelated, and dynamically obtained knowledge, and should have a way to simply specify what knowledge is to be changed. This requires the existence of a language for exacting such changes (or updates), which takes in consideration the addition/deletion and changes of rules, thereby automating the task of dealing with inconsistencies arising from those updates. To address this issue, we resort to recent developments in the field of Logic Programming, and show how the framework of EVOLP (EVOlving Logic Programs) can be put to work to model such reactive and updateable rule bases, bringing an important added value to RuleML. We make our case by exhibiting a detailed application example of how EVOLP can be used to express updateable RuleML rule bases, employing it to define an evolving e-mail Personal Assistant Agent.

Partial Models of Extended Generalized Logic Programs

Lecture Notes in Computer Science, 2000

In recent years there has been an increasing interest in extensions of the logic programming para... more In recent years there has been an increasing interest in extensions of the logic programming paradigm beyond the class of normal logic programs motivated by the need for a satisfactory respresentation and processing of knowledge. An important problem in this area is to nd an adequate declarative semantics for logic programs. In the present paper a general preference criterion is proposed that selects the `intended' partial models of extended generalized logic programs which is a conservative extension of the stationary semantics for normal logic programs of 13], 15] and generalizes the WFSX-semantics of 12]. The presented preference criterion de nes a partial model of an extended generalized logic program as intended if it is generated by a stationary chain. The GWFSX-semantics is de ned by the set-theoretical intersection of all stationary generated models, and thus generalizes the results from 9] and 1].

Computing environment-aware agent behaviours with logic program updates

Logic Based Program Synthesis and Transformation, 2002

The ability of reacting to changes in the external environment is of crucial importance within th... more The ability of reacting to changes in the external environment is of crucial importance within the context of software agents. Such feature must however be suitably reconciled with a more deliberative rational behaviour. In this paper we show how different behaviours of environment-aware agents can be naturally specified and computed in terms of logic program updates. Logic program updates are specified, in our setting, by the language of updates LUPS. We show how such language can be used to model the more reactive behaviours, while keeping the more deliberative features provided by its underlying Dynamic Logic Programming paradigm. The obtained declarative semantics sets a firm basis for the development, implementation, and analysis of environmentaware agents.

An Event-Condition-Action Logic Programming Language

Lecture Notes in Computer Science, 2006

Event-Condition-Action (ECA) languages are an intuitive and powerful paradigm for programming rea... more Event-Condition-Action (ECA) languages are an intuitive and powerful paradigm for programming reactive systems. Usually, important features for an ECA language are reactive and reasoning capabilities, the possibilities to express complex actions and events and a declarative semantics. In this paper, we introduce ERA, an ECA language based on the framework of logic programs updates that, together with these features, also exhibits capabilities to integrate external updates and perform self updates to its knowledge (data and classical rules) and behaviour (reactive rules).

Debugging by diagnosing assumptions

Lecture Notes in Computer Science

Belief, provability, and logic programs

Journal of Applied Non-Classical Logics, 1995

The main goal of this paper is to establish a nonmonotonic epistemic logic EB with two modalities... more The main goal of this paper is to establish a nonmonotonic epistemic logic EB with two modalities -provability and belief -capable of expressing and comparing a variety of known semantics for extended logic programs, and clarify their meaning. In particular we present here, for the first time, embeddings into epistemic logic of logic programs extended with a second kind of negation under the wellfounded semantics, and contrast them to the recent embeddings into autoepistemic logics of such programs under stable models based semantics. Because of the newly established relationship between our epistemic logic EB and extended program semantics, the former benefits from the procedures and implementations of the latter, and can be applied to at least the same class of AI problems that the latter can. Moreover, one issue of epistemic logic introduced here, belief revision, can profit from adapting techniques employed by the latter for contradiction removal. Furthermore, the language of the epistemic logic presented here being more general than that of extended programs, it offers a basic tool for further generalizations of the latter, for instance regarding disjunction and modal operators.

Argumentation-based Proof for an Argument in a Paraconsistent Setting

The paradigm of argumentation has been used in the literature to assign meaning to knowledge base... more The paradigm of argumentation has been used in the literature to assign meaning to knowledge bases in general, and logic programs in particular. With this paradigm, rules of logic program are viewed as encoding arguments of an agent, and the meaning of the program is determined by those arguments that somehow (depending on the specific semantics) can defend themselves from the attacks of others arguments, named acceptable arguments. In previous work we presented an argumentation based declarative semantics allowing paraconsistent reasoning and also dealing with sets of logic programs that argue and cooperate among each other. In this paper we focus on the properties of this semantics in what regards paraconsistency and propose a procedure for proving an argument according to that semantics.

Multi-dimensional logic programming

According to the paradigm of Dynamic Logic Programming, knowledge is given by a set of theories (... more According to the paradigm of Dynamic Logic Programming, knowledge is given by a set of theories (encoded as logic programs) representing different states of the world. Different states may represent time (as in updates), specificity (as in taxonomies), strength of the updating instance (as in the legislative domain), hierarchical position of knowledge source (as in organizations), etc. The mutual relationships extant between different states are used to determine the semantics of the combined theory composed of all individual ...

SLX-A top-down derivation procedure for programs with explicit negation

International Logic Programming Symp, Nov 1, 1994

In this paper we define a sound and (theoretically) complete top-down derivation procedure for a ... more In this paper we define a sound and (theoretically) complete top-down derivation procedure for a well-founded semantics of logic programs extended with explicit negation (WFSX). By its nature, it is amenable to a simple interpreter implementation in Prolog, and readily allows pre-processing into Prolog, showing promise as an efficient basis for further development. The derivation method is directly inspired on the semantic AND-tree characterization of WFSX in our paper [2], but docs not require knowledge of it. In fact, that ...

SLWV—A theorem prover for logic programming

Extensions of Logic Programming, 1993

The purpose of this work is to define a theorem prover that retains the procedural aspects of log... more The purpose of this work is to define a theorem prover that retains the procedural aspects of logic programing. The proof system we propose (SLWV-resolution. for Selected Linear Without contrapositive clause Variants)) is defined for a set of clauses in the implicational form (keeping to the form of logic programs). not requiring contrapositives, and has an execution method that respects the execution order of literals in a clause, preserving the procedural flavor of logic programming. SLWV-resolution can be seen as a combination of ...

Dynamic Logic Programming

Belief Revision in Non-Monotonic Reasoning and Logic Programming

Fundamenta Informaticae

A Language for Updates with Multiple Dimensions

Dynamic Logic Programming (DLP) was introduced to deal with knowledge about changing worlds, by a... more Dynamic Logic Programming (DLP) was introduced to deal with knowledge about changing worlds, by assigning semantics to sequences of generalized logic programs, each of which represents a state of the world. These states permit the representation, not only of time, but also of specificity, strength of updating instance, hierarchical position of the knowledge source, etc. Subsequently, the Language of Updates LUPS was introduced to allow for the association, with each state, of a set of transition rules. It thereby provides for an interleaving sequence of states and transition rules within an integrated declarative framework. DLP (and LUPS), because defined only for a linear sequence of states, cannot deal simultaneously with more than a single dimension (e.g. time, hierarchies,...). To overcome this limitation, Multi-dimensional Dynamic Logic Programming (MDLP) was therefore introduced, so as to make it possible to organize states into arbitrary acyclic digraphs (DAGs). In this paper we now extend LUPS, setting forth a Language for Multidimensional Updates (MLUPS). MLUPS admits the specification of flexible evolutions of such DAG organized logic programs, by allowing not just the specification of the logic programs representing each state, but to the evolution of the DAG topology itself as well.

Preliminary exploration on actions as updates

Agp, 1999

This paper reports on the use of logic program updates to models actions that bring about changes... more This paper reports on the use of logic program updates to models actions that bring about changes in knowledge states describing the world and its rules. The LUPS language is employed to specify concurrent update rules to model actions that depend on, and change, rule rich world states, not described simply by propositional uents. This language and corresponding semantics, whose original stable semantics we generalize to the well-founded setting, is brie y recapitulated here. The advantages of our approach to modelling actions as updates are brought out by a number of telling examples, especially conceived for the purpose. They have been test run in our implementation of LUPS, though the latter is not described here for lack of space.

Updates of Logic Programs by Logic Programs

In this paper we i n v estigate updates of knowledge bases represented by logic programs. In orde... more In this paper we i n v estigate updates of knowledge bases represented by logic programs. In order to represent negative information, we use generalized logic programs which allow default negation not only in rule bodies but also in their heads.We start by i n troducing the notion of an update P U of a logic program P by another logic program U. Subsequently, w e provide a precise semantic characterization of P U, and study some basic properties of program updates. In particular, we show that our update programs generalize the notion of interpretation update. We then extend this notion to compositional sequences of logic programs updates P1 P2 : : : , de ning a dynamic program update, and thereby i n troducing the paradigm of dynamic logic programming. This paradigm signi cantly facilitates modularization of logic programming, and thus modularization of non-monotonic reasoning as a whole. Speci cally, suppose that we are given a set of logic program modules, each describing a di erent state of our knowledge of the world. Di erent states may represent di erent time points or di erent sets of priorities or perhaps even di erent viewpoints. Consequently, program modules may contain mutually contradictory as well as overlapping information. The role of the dynamic program update is to employ the mutual relationships existing between di erent modules to precisely determine, at any given module composition stage, the declarative a s w ell as the procedural semantics of the combined program resulting from the modules.