Marco Manna

The third answer set programming competition: preliminary report of the system competition track

Answer Set Programming is a well-established paradigm of declarative programming in close relationship with other declarative formalisms such as SAT Modulo Theories, Constraint Handling Rules, FO(.), PDDL and many others. Since its first informal editions, ASP systems are compared in the nowadays customary ASP Competition. The Third ASP Competition, as the sequel to the ASP Competitions Series held at the University of Potsdam in Germany (2006-2007) and at the University of Leuven in Belgium in 2009, took place at the University of Calabria (Italy) in the first half of 2011. Participants competed on a selected collection of declarative specifications of benchmark problems, taken from a variety of domains as well as real world applications, and instances thereof. The Competition ran on two tracks: the Model & Solve Competition, held on an open problem encoding, on an open language basis, and open to any kind of system based on a declarative specification paradigm; and the System Competition, held on the basis of fixed, public problem encodings, written in a standard ASP language. This paper briefly discuss the format and rationale of the System competition track, and preliminarily reports its results.

Team-building with answer set programming in the gioia-tauro seaport

The seaport of Gioia Tauro is the largest transshipment terminal of the Mediterranean coast. A crucial management task for the companies operating in the seaport is team-building: the problem of properly allocating the available personnel for serving the incoming ships. Teams have to be carefully arranged in order to meet several constraints, such as allocation of employees with appropriate skills, fair distribution of the working load, and turnover of the heavy/dangerous roles. This makes team-building a hard and expensive task requiring several hours of manual preparation per day. In this paper we present a system based on Answer Set Programming for the automatic generation of the teams of employees in the seaport of Gioia Tauro. The system is currently exploited in the Gioia Tauro seaport by ICO BLG, a company specialized in automobile logistics.

A Logic-Based System for e-Tourism

In this paper we present a successful application of logic programming for e-tourism: the iTravel system. The system exploits two technologies that are based on the state-of-the-art computational logic system DLV: (i) a system for ontology representation and reasoning, called OntoDLV; and, (ii) H

ASP at work: spin-off and applications of the DLV system

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Disjunctive datalog with existential quantifiers: Semantics, decidability, and complexity issues

LeX a semantic information-extraction tool. The core of iTravel is an ontology which models the domain of tourism offers. The ontology is automatically populated by extracting the information contained in the tourism leaflets produced by tour operators. A set of specifically devised logic programs is used to reason on the information contained in the ontology for selecting the holiday packages that best fit the customer needs. An intuitive web-based user interface eases the task of interacting with the system for both the customers and the operators of a travel agency.

Consistent query answering via ASP from different perspectives: Theory and practice

Answer Set Programming (ASP) is a declarative language for knowledge representation and reasoning. After its proposal, in a seminal paper by Michael Gelfond and Vladimir Lifschitz dated in 1988, ASP has been the subject of a broad theoretical research-work, ranging from linguistic extensions and semantic properties to evaluation algorithm and optimization techniques. Later on, the availability of a number of efficient systems made ASP a powerful tool for the fast development of knowledge-based applications. In this paper, we report on the ongoing effort aimed at the industrial exploitation of DLV- one of the most popular ASP systems - in the area of Knowledge Management. Two spinoff companies of University of Calabria are involved in such an exploitation: Dlvsystem Srl and Exeura Srl. They have specialized DLV into some Knowledge Management products for Text Classification, Information Extraction, and Ontology Representation and Reasoning, which have allowed to develop a number of successful real-world applications.

On the complexity of ontological reasoning under disjunctive existential rules

Datalog is one of the best-known rule-based languages, and extensions of it are used in a wide context of applications. An important Datalog extension is Disjunctive Datalog, which significantly increases the expressivity of the basic language. Disjunctive Datalog is useful in a wide range of applications, ranging from Databases (e.g., Data Integration) to Artificial Intelligence (e.g., diagnosis and planning under incomplete knowledge). However, in recent years an important shortcoming of Datalog-based languages became evident, e.g. in the context of data-integration (consistent query-answering, ontology-based data access) and Semantic Web applications: The language does not permit any generation of and reasoning with unnamed individuals in an obvious way. In general, it is weak in supporting many cases of existential quantification. To overcome this problem, Datalogex has recently been proposed, which extends traditional Datalog by existential quantification in rule heads. In this work, we propose a natural extension of Disjunctive Datalog and Datalogex, called Datalogexor, which allows both disjunctions and existential quantification in rule heads and is therefore an attractive language for knowledge representation and reasoning, especially in domains where ontology-based reasoning is needed. We formally define syntax and semantics of the language Datalogexor, and provide a notion of instantiation, which we prove to be adequate for Datalogexor. A main issue of Datalogex and hence also of Datalogexor is that decidability is no longer guaranteed for typical reasoning tasks. In order to address this issue, we identify many decidable fragments of the language, which extend, in a natural way, analog classes defined in the non-disjunctive case. Moreover, we carry out an in-depth complexity analysis, deriving interesting results which range from Logarithmic Space to Exponential Time.

Combining decidability paradigms for existential rules

A data integration system provides transparent access to different data sources by suitably combining their data, and providing the user with a unified view of them, called global schema. However, source data are generally not under the control of the data integration process, thus integrated data may violate global integrity constraints even in presence of locally-consistent data sources. In this scenario, it may be anyway interesting to retrieve as much consistent information as possible. The process of answering user queries under global constraint violations is called consistent query answering (CQA). Several notions of CQA have been proposed, e.g., depending on whether integrated information is assumed to be sound, complete, exact or a variant of them. This paper provides a contribution in this setting: it uniforms solutions coming from different perspectives under a common ASP-based core, and provides query-driven optimizations designed for isolating and eliminating inefficiencies of the general approach for computing consistent answers. Moreover, the paper introduces some new theoretical results enriching existing knowledge on decidability and complexity of the considered problems. The effectiveness of the approach is evidenced by experimental results. To appear in Theory and Practice of Logic Programming (TPLP).

H\imathLεX: A System for Semantic Information Extraction from Web Documents

Ontology-based data access is an emerging yet powerful technology that allows to enhance a classical relational database with an ontology in order to infer new intensional knowledge. Recently, Datalog+/- was introduced with the purpose of providing tractable reasoning algorithms for expressive ontology languages. In this framework, Datalog is extended by features such as existential quantification in rule heads, and at the same time the rule syntax is restricted to guarantee decidability, and also tractability, of relevant reasoning tasks. In this paper, we enrich Datalog even more by allowing not only existential quantification but also disjunction in rule heads, and we investigate the complexity of reasoning under the obtained formalism.

Taming primary key violations to query large inconsistent data via ASP

Existential rules are Datalog rules extended with existential quantifiers in rule-heads. Three fundamental restriction paradigms that have been studied for ensuring decidability of query answering under existential rules are weak-acyclicity, guardedness and stickiness. Towards the identification of even more expressive decidable languages, several attempts have been conducted to consolidate weak-acyclicity with the other two paradigms. However, it is not clear how guardedness and stickiness can be merged; this is the subject of this paper. A powerful and flexible condition, called tameness, is proposed, which allows us to consolidate in an elegant and uniform way guardedness with stickiness.