Decidable Reasoning in Terminological Knowledge Representation Systems

Terminological knowledge representation systems (TKRSs) are tools for designing and using knowledge bases that make use of terminological languages (or concept languages). We analyze from a theoretical point of view a TKRS whose capabilities go beyond the ones of presently available TKRSs. The new features studied, often required in practical applications, can be summarized in three main points. First, we consider a highly expressive terminological language, called ALCNR, including general complements of concepts, number restrictions and role conjunction. Second, we allow to express inclusion statements between general concepts, and terminological cycles as a particular case. Third, we prove the decidability of a number of desirable TKRS-deduction services (like satisfiability, subsumption and instance checking) through a sound, complete and terminating calculus for reasoning in ALCNR-knowledge bases. Our calculus extends the general technique of constraint systems. As a byproduct of the proof, we get also the result that inclusion statements in ALCNR can be simulated by terminological cycles, if descriptive semantics is adopted.Comment: See http://www.jair.org/ for any accompanying file

Evaluation von Wissensrepräsentationssystemen

Ziel dieses Berichtes ist eine Evaluation von aktuellen Wissensrepräsentationssystemen, insbesondere terminologischen Logiken. Nach Aufstellung der relevanten Evaluationskriterien erfolgt zunächst eine allgemeine Behandlung von KL-ONE - der Urmutter der terminologischen Logiken -, wobei schon einige inhärente kritische Punkte der zu behandelnden Systeme aufgezeigt werden. Anschließend werden Syntax- und Semantikdefinitionen von KL-ONE-Derivaten vorgestellt, um deren Sprachumfang zu vergleichen. Neben den gängigen KL-ONE-Derivaten wird auch die in LILOG verwendete Repräsentationssprache vorgestellt. Abschließend erfolgt ein zusammenfassender Vergleich der Systeme. Hierbei stellt sich heraus, dass insbesondere die Systeme LOOM, CLASSIC, KRIS und BACK bezüglich des verwendeten Sprachumfangs und der Effizienz der Inferenzen gut abschneiden. Die Systeme BACK und KRIS sind dabei für Verbmobil besonders relevant, da sie relativ leicht verfügbar sind. Außerdem zeichnet sich BACK durch ein gut strukturiertes Handbuch aus und eine schnelle neue Implementierung In C. Kritisch bei allen vorgestellten Systemen ist die Darstellung zeitlicher Zusammenhänge (Ereignisse, Aktionen); hierzu liegen jedoch schon Forschungsergebnisse für die Erweiterung der terminologischen Sprachen vor

Subsumption algorithms for concept languages

We investigate the subsumption problem in logic-based knowledge representation languages of the KL-ONE family and give decision procedures. All our languages contain as a kernel the logical connectives conjunction, disjunction, and negation for concepts, as well as role quantification. The algorithms are rule-based and can be understood as variants of tableaux calculus with a special control strategy. In the first part of the paper, we add number restrictions and conjunction of roles to the kernel language. We show that subsumption in this language is decidable, and we investigate sublanguages for which the problem of deciding subsumption is PSPACE-complete. In the second part, we amalgamate the kernel language with feature descriptions as used in computational linguistics. We show that feature descriptions do not increase the complexity of the subsumption problem

Terminological cycles in KL-ONE-based knowledge representation languages

Cyclic definitions are often prohibited in terminological knowledge representation languages, because, from a theoretical point of view, their semantics is not clear and, from a practical point of view, existing inference algorithms may go astray in the presence of cycles. In this paper we consider terminological cycles in a very small KL-ONE-based language. For this language, the effect of the three types of semantics introduced by Nebel (1987, 1989, 1989a) can be completely described with the help of finite automata. These descriptions provide a rather intuitive understanding of terminologies with cyclic definitions and give insight into the essential features of the respective semantics. In addition, one obtains algorithms and complexity results for subsumption determination. The results of this paper may help to decide what kind of semantics is most appropriate for cyclic definitions, not only for this small language, but also for extended languages. As it stands, the greatest fixed-point semantics comes off best. The characterization of this semantics is easy and has an obvious intuitive interpretation. Furthermore, important constructs--such as value-restriction with respect to the transitive or reflexive-transitive closure of a role--can easily be expressed

Abstraction, extension and structural auditing with the UMLS semantic network

The Unified Medical Language System (UMLS) is a two-level biomedical terminological knowledge base, consisting of the Metathesaurus (META) and the Semantic Network (SN), which is an upper-level ontology of broad categories called semantic types (STs). The two levels are related via assignments of one or more STs to each concept of the META. Although the SN provides a high-level abstraction for the META, it is not compact enough. Various metaschemas, which are compact higher-level abstraction networks of the SN, have been derived. A methodology is presented to evaluate and compare two given metaschemas, based on their structural properties. A consolidation algorithm is designed to yield a consolidated metaschema maintaining the best and avoiding the worst of the two given metaschemas. The methodology and consolidation algorithm were applied to the pair of heuristic metaschemas, the top-down metaschema and the bottom-up metaschema, which have been derived from two studies involving two groups of UMLS experts. The results show that the consolidated metaschema has better structural properties than either of the two input metaschemas. Better structural properties are expected to lead to better utilization of a metaschema in orientation and visualization of the SN. Repetitive consolidation, which leads to further structural improvements, is also shown. The META and SN were created in the absence of a comprehensive curated genomics terminology. The internal consistency of the SN\u27s categories which are relevant to genomics is evaluated and changes to improve its ability to express genomic knowledge are proposed. The completeness of the SN with respect to genomic concepts is evaluated and conesponding extensions to the SN to fill identified gaps are proposed. Due to the size and complexity of the UMLS, errors are inevitable. A group auditing methodolgy is presented, where the ST assignments for groups of similar concepts are audited. The extent of an ST, which is the group of all concepts assigned this ST, is divided into groups of concepts that have been assigned exactly the same set of STs. An algorithm finds subgroups of suspicious concepts. The auditor is presented with these subgroups, which purportedly exhibit the same semantics, and thus he will notice different concepts with wrong or missing ST assignments. Another methodology partitions these groups into smaller, singly rooted, hierarchically organized sets used to audit the hierarchical relationships. The algorithmic methodologies are compared with a comprehensive manual audit and show a very high error recall with a much higher precision than the manual exhaustive review

Epistemic Reasoning in OWL 2 DL

We extend the description logic SROIQ (OWL 2 DL) with the epistemic operator K and argue that unintended effects occur when imposing the semantics traditionally employed. Consequently, we identify the most expressive DL for which the traditional approach can still be adapted. For the epistemic extension of SROIQ and alike expressive DLs, we suggest a revised semantics that behaves more intuitively in these cases and coincides with the traditional semantics on less expressive DLs

Terminological cycles in KL-ONE-based knowledge representation languages

Cyclic definitions are often prohibited in terminological knowledge representation languages, because, from a theoretical point of view, their semantics is not clear and, from a practical point of view, existing inference algorithms may go astray in the presence of cycles. In this paper we consider terminological cycles in a very small KL-ONE-based language. For this language, the effect of the three types of semantics introduced by Nebel (1987, 1989, 1989a) can be completely described with the help of finite automata. These descriptions provide a rather intuitive understanding of terminologies with cyclic definitions and give insight into the essential features of the respective semantics. In addition, one obtains algorithms and complexity results for subsumption determination. The results of this paper may help to decide what kind of semantics is most appropriate for cyclic definitions, not only for this small language, but also for extended languages. As it stands, the greatest fixed-point semantics comes off best. The characterization of this semantics is easy and has an obvious intuitive interpretation. Furthermore, important constructs--such as value-restriction with respect to the transitive or reflexive-transitive closure of a role--can easily be expressed

ANSwER-Sistema informativo ambientale basato su ontologia e logica Fuzzy

2006/2007Le fonti dati rilevanti per il monitoraggio dell’avifauna delle lagune friulane, previsto dal progetto ANSER (Programma INTERREG IIIA Transfrontaliero Adriatico), sono alimentate da tre diverse metodologie di censimento, una metodologia di cattura/marcatura e una metodologia di tracciamento radio telemetrico. L’ampio spettro di informazioni a riguardo è confluito in un sistema informativo ambientale che 1) traduce tutti i dati in Ecological Metadata Language (EML) seguendo un unico modello sintattico orientato agli oggetti, 2) lo arricchisce semanticamente con una ontologia di dominio basata sulla Logica Descrittiva, 3) ne analizza le performance predittive, validando, attraverso un sistema inferenziale fuzzy, il modello teorico rispetto ai dati raccolti su campo. I risultati più importanti sono descrivibili così: 1) l’eliminazione completa di eterogeneità tra dataset ha permesso di atomizzare le tuple, reificando in un’unica super-classe di eventi nel tempo, i contatti tra operatore e animale in un determinato luogo; 2) l’ontologia OWL-DL ha determinato in maniera consistente l’appartenenza delle specie alle guild considerate e la relativa attrazione verso i diversi habitat disponibili; 3) il modello fuzzy ha rivelato che le informazioni sull’habitat e sulla profondità delle acque nel punto di monitoraggio, influiscono differentemente sulla predizione di abbondanza delle diverse guild esaminate.XX Ciclo196

An investigation of the applicability of terminological reasoning to application-independent software-analysis

This work is a first investigation of an observation noted as possibly promising: The problem of application-independent recognition of given elements from the architecture of an unknown software system to be analyzed can be conceived as a special case of the classification problem in a terminological reasoning system if supplied with a suitably defined taxonomy for software-elements. This problem, however, has been solved in certain terminological reasoning systems (TRSs). To the end of investigating this idea, the availability of a TRS was necessary (provided at DFKI by viltlle of the KRIS-system) as well as stating clearly the envisaged application-independent software-elements, followed by a concept taxonomy expressible in KRIS and delivering the desired results. Furthermore, a tool had to be developed to analyze software (i.e ., the source code) and generate the input information for the taxonomy from that. Stating application-independent complete and correct conditions for the role of an element within a software system turned out to be feasible for only a few basic concepts, because software employs at least up to now too few standardized concepts. The translation of the feasible concepts to KRIS resulted in problems of the expressive power of TRSs that were recognized as fundamental. The root of this problem spawned a new language construction for KRIS. Under the assumption of this new construction, a taxonomy of software-elements was formulated. However, as the incorporation of this construct, while recognized as feasible, would exceed the scope of this work and is therefore still to come, it has not been possible so far to test the formulated taxonomy. Hoping this will become possible in the future, the tool for input generation was developed nonetheless. The chosen programming language to be processed is C, as there was an initial tool already available for it. Thus the concluding judgment of this investigation is still to come

Second Annual Workshop on Space Operations Automation and Robotics (SOAR 1988)

Papers presented at the Second Annual Workshop on Space Operation Automation and Robotics (SOAR '88), hosted by Wright State University at Dayton, Ohio, on July 20, 21, 22, and 23, 1988, are documented herein. During the 4 days, approximately 100 technical papers were presented by experts from NASA, the USAF, universities, and technical companies. Panel discussions on Human Factors, Artificial Intelligence, Robotics, and Space Systems were held but are not documented herein. Technical topics addressed included knowledge-based systems, human factors, and robotics