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Fischer, D.H.: From thesauri towards ontologies? (1998)
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- Abstract
- The ISO 2788 guidelines for monolingual thesauri contain a differentiation of "the hierarchical relationship" into "generic", "partitive", and "instance", which, for purposes of document retrieval, was deemed adequate. However, ontologies, designed as language inventories for a wider scope of knowledge representation, are based on all these and some more logical differentiations. Rereading the ISO 2788 standard and inspecting the published Cyc Upper Ontology, it is argued that the adoption of the document-retrieval definition of subsumption generally prevents the conception or use of a thesaurus as a substructure of an ontology of the new kind as constructed for AI applications. When a thesaurus is used for fact description and inference on fact descriptions, the instance-of relationship too should be reconsidered: It may also link concepts and metaconcepts, and then its distinction from subsumption is needed. The treatment of the instance-of relationship in thesauri, the Cyc Upper Ontology, and WordNet is described from this perspective
- Theme
- Konzeption und Anwendung des Prinzips Thesaurus
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Fischer, D.H.: Converting a thesaurus to OWL : Notes on the paper "The National Cancer Institute's Thesaurus and Ontology" (2004)
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- Abstract
- The paper analysed here is a kind of position paper. In order to get a better under-standing of the reported work I used the retrieval interface of the thesaurus, the so-called NCI DTS Browser accessible via the Web3, and I perused the cited OWL file4 with numerous "Find" and "Find next" string searches. In addition the file was im-ported into Protégé 2000, Release 2.0, with OWL Plugin 1.0 and Racer Plugin 1.7.14. At the end of the paper's introduction the authors say: "In the following sections, this paper will describe the terminology development process at NCI, and the issues associated with converting a description logic based nomenclature to a semantically rich OWL ontology." While I will not deal with the first part, i.e. the terminology development process at NCI, I do not see the thesaurus as a description logic based nomenclature, or its cur-rent state and conversion already result in a "rich" OWL ontology. What does "rich" mean here? According to my view there is a great quantity of concepts and links but a very poor description logic structure which enables inferences. And what does the fol-lowing really mean, which is said a few lines previously: "Although editors have defined a number of named ontologic relations to support the description-logic based structure of the Thesaurus, additional relation-ships are considered for inclusion as required to support dependent applications."
According to my findings several relations available in the thesaurus query interface as "roles", are not used, i.e. there are not yet any assertions with them. And those which are used do not contribute to complete concept definitions of concepts which represent thesaurus main entries. In other words: The authors claim to already have a "description logic based nomenclature", where there is not yet one which deserves that title by being much more than a thesaurus with strict subsumption and additional inheritable semantic links. In the last section of the paper the authors say: "The most time consuming process in this conversion was making a careful analysis of the Thesaurus to understand the best way to translate it into OWL." "For other conversions, these same types of distinctions and decisions must be made. The expressive power of a proprietary encoding can vary widely from that in OWL or RDF. Understanding the original semantics and engineering a solution that most closely duplicates it is critical for creating a useful and accu-rate ontology." My question is: What decisions were made and are they exemplary, can they be rec-ommended as "the best way"? I raise strong doubts with respect to that, and I miss more profound discussions of the issues at stake. The following notes are dedicated to a critical description and assessment of the results of that conversion activity. They are written in a tutorial style more or less addressing students, but myself being a learner especially in the field of medical knowledge representation I do not speak "ex cathedra".
- Theme
- Konzeption und Anwendung des Prinzips Thesaurus
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Fischer, D.H.: ¬Ein Lehrbeispiel für eine Ontologie : OpenCyc (2004)
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- Abstract
- Es wird ein einführender Überblick über das seit Frühjahr 2002 allgemein verfügbare Ontologiesystem OpenCyc und seine gegenwärtige Wissensbasis gegeben. Das System ist Prototyp eines logikbasierten Wissensrepräsentationssystems und der lnhalt der fortschreib-baren Wissensbasis ist eine universelle Dachontologie, die als ein Extrakt aus langjähriger Erfahrung mit ihrer Anwendung angesehen werden kann. Die Wissensrepräsentationssprache CycL von OpenCyc konkurriert mit der bisher weniger ausdrucksstarken Sprache OWL, die von den W3C-Gremien für das "Semantic Web"standardisiert wird.
- Content
- Wer über Ontologien und Ontologiesysteme spricht, sollte auch das System OpenCyc kennen. Aber was heißt hier "kennen"? Ich habe mich als Leser und experimentierender Benutzer mit diesem System intensiver befasst und unter einer Reihe von spezielleren Fragen an das System meine Erfahrungen in einigen Arbeitspapieren protokolliert. Sie sind über das Internet zugänglich'. Hier möchte ich der allgemeinen Orientierung über OpenCyc dienende Anmerkungen dazugeben. Bereits eine Recherche mit der Suchmaschine Google, den Suchworten "Cyc OpenCyc" und Beschränkung der Quellen auf Sprache Deutsch oder Herkunft Deutschland erbringt einige der auch hier wiedergegebenen vordergründigen Informationen, sie zeigt aber auch, dass sich Professoren oder Studenten im Jahr 2003 z.B. in Ulm, Heidelberg, Berlin, Bamberg, Bonn und Darmstadt mit dem Thema Cyc und OpenCyc beschäftigt haben entsprechend meiner Titelthese.
Das Projekt Cyc ist im Jahre 1984 angetreten mit der Zielsetzung, im großen Maßstab Alltags- und enzyklopädisches Wissen in einem einheitlichen System zu formalisieren im Gegensatz zu den bisherigen Versuchen der jeweiligen Repräsentation sektoralen Expertenwissens. Nachdem man sich dem Mythos Cyc zunächst nur über Publikationen nähern konntet, wurde dann 1997 als Textdatei Cycs "Upper Ontology" durch die Firma Cycorp Inc. zugänglich gemacht. Sie enthielt aber einiges nicht, was beschrieben worden war: z.B. Regeln und die Bindung von Aussagen an "Mikrotheorien". Entsprechend dieser Beschränkung war es mir möglich, den Inhalt dieser Datei strukturell verlustfrei in mein objektorientiertes, generisches Thesaurussystem "TerminologyFramework" einzubringen. Im April 200z wurden dann unter dem Namen OpenCyc nicht nur der Inhalt eines Auszugs aus Cycorps Ontologie, sondern auch zugehörige Werkzeuge zum lesenden Stöbern, Ändern und Schließen in einem ersten Release 0.6 zugänglich. Dazu findet man reichlich tutorielles Material, jedoch ist es nicht exakt abgestimmt auf die aktuell vorliegende Wissensbasis, sowie allerhand Dokumentation; vor allem aber findet man zum Herunterladen das Softwarepaket samt Wissensbasis für Windows NT/2000/XP- oder für Linux-Systeme. In welchem Verhältnis das nun kostenlos mit einer "GNU Lesser General Public License" verfügbare OpenCyc zu dem kommerziellen "Full Cyc" der Firma Cycorp steht, darüber weiß ich nichts aus erster Hand; die von mir für OpenCyc ermittelten Zahlen (s.u.) stehen zu neueren Angaben für Cyc in einem Größenordnungsverhältnis von ca. 1 zu 10. Informationen über realisierte Anwendungen kann man der Firmenselbstdarstellung$ und den von dort erreichbaren "white papers" entnehmen. Auf der Firmeneingangsseite findet man in Gestalt einer Pyramide eine Inhaltsübersicht der Ontologie von Cyc (siehe Abbildung 1): Beim Darüberfahren mit der Maus wird das dort wie auch hier kaum leserliche Kleingedruckte im Feld links oben lesbar und durch Klicken wird eine Inhaltsbeschreibung des jeweiligen Begriffsbereichs im Feld unten gegeben. OpenCyc stellt wohl einen exemplarischen Auszug aus dem oberen Teil der Pyramide oberhalb "Domain-Specific Knowledge" dar.
- Source
- Information - Wissenschaft und Praxis. 55(2004) H.3, S.139-142
