taken from Schulze-Kremer Steffen Ontologies - What, why and how? Cartic Ramakrishnan LSDIS lab University of Georgia

taken from Schulze-Kremer Steffen What is Ontology The study of being qua being: the study of possible The study of the nature of possible: ontology as the theory of distinctions among possibilia The study of the most general characteristics that anything must have in order to count as a (certain kind of) being or entity.

taken from Schulze-Kremer Steffen Definitions Ontology (capital “o”): –a philosophical discipline. An ontology (lowercase “o”): –specific artifact designed with the purpose of expressing the intended meaning of a vocabulary

taken from Schulze-Kremer Steffen What is an ontology? A shared vocabulary Plus … A specification (actually, a characterization) of the intended meaning of that vocabulary...i.e., an ontology accounts for the commitment of a language to a certain conceptualization “An ontology is a specification of a conceptualization” [Gruber 95]

taken from Schulze-Kremer Steffen Models and Conceptualizations

taken from Schulze-Kremer Steffen Capturing Intended Meaning First order logic is ontologically neutral Logical KBs often rely on natural language to convey intended meaning

taken from Schulze-Kremer Steffen Intended Models An ontology consisting of just a vocabulary is of little use - Unintended interpretations need to be excluded Models M(L) Intended models I K (L)

taken from Schulze-Kremer Steffen What is a conceptualization? Conceptualization of scene 1: Scene 1: blocks on a table

taken from Schulze-Kremer Steffen What is a conceptualization? The same conceptualization? Scene 2: a different arrangement of blocks

taken from Schulze-Kremer Steffen What is a conceptualization Conceptualization: the formal structure of reality as perceived and organized by an agent, independently of: –the vocabulary used (i.e., the language used) –the actual occurence of a specific situation Different situations involving the same objects, described by different vocabularies, may share the same conceptualization. apple mela same conceptualization LILI LELE

taken from Schulze-Kremer Steffen Relations vs. Conceptual Relations ordinary relations are defined on a domain D: conceptual relations are defined on a domain space (Montague-style semantics)

taken from Schulze-Kremer Steffen Ontologies constrain the intended meaning Conceptualization C Language L Commitment K= Ontology Models M(L) Intended models I K (L)

taken from Schulze-Kremer Steffen Levels of Ontological Depth (SSK would disagree) Lexicon –Vocabulary with NL definitions Simple Taxonomy Thesaurus –Taxonomy plus related-terms Relational Model (NOT DB) –Unconstrained use of arbitrary relations Fully Axiomatized Theory

taken from Schulze-Kremer Steffen ontologies - ontology Ontology –study of being as a branch of philosophy Ontologies –result of the analysis of a particular domain of interest (possibly as broad as the universe) –instantiation of a concrete ontological model of that domain

taken from Schulze-Kremer Steffen Ontologies-ontology Ontologies are to a large extent in principle language independent Varying scope and content of domain ontologies –upper-level ontologies (Cyc) –application ontologies (??) –task ontologies (??)

taken from Schulze-Kremer Steffen Definitions - Yes, Again!! Here are three definitions of domain ontologies –(i) "System of categories accounting for a particular vision of the world." [Guarino] –(ii) "Specification of a conceptualization." [Gruber] –(iii) "Concise and unambiguous description of principle relevant entities with their potential, valid relations to each other." [guess who?]

taken from Schulze-Kremer Steffen What an Ontology is NOT!!! not a collection of facts arising from a specific situation not a model of an application domain not a database schema not a knowledge base not a taxonomy not a vocabulary or dictionary not a semantic net

taken from Schulze-Kremer Steffen Why ontologies? Data integration –Semantic integration of n databases without the great “o” would require n*n integration attempts with the great “o” would require n attempts Data annotation –full-fledged ontology not required since main purpose is fixed unique reference point in the for of controlled vocabulary

taken from Schulze-Kremer Steffen ENTER GO!!! Not ontology but vocabulary –ISA vs. instance-of –PART-OF vs “made of”, “belongsto” –80% concepts lack explicit defn. –700 concepts are orphans –no clear design principle –no IC for consistency –where do new concepts go? –No grammar rules for to combine concept –Not The Gene Ontology but 3

taken from Schulze-Kremer Steffen References Guarino, N. (1998). Some Ontological Principles for Designing Upper Level Lexical Resources. In: Proceedings of First International Conference on Language Resources and Evaluation. Granada, Spain. Gruber, T. R. (1993). Knowledge Acquisition 5, Schulze-Kremer, S. (1998) Ontologies for molecular biology