F12: SEMANTICS and ONTOLOGIES

Transcription

1 F12: SEMANTICS and ONTOLOGIES The ATHENA Consortium. 1 A mini-lesson in semantics s e m a n t i c s? How do you do, Semantics? How do you do semantics? The ATHENA Consortium. 2

2 Semantics Semantics ancient Greek for meaning σηµαίνω I signal, sign, show Semantics has become a buzzword or even a fuzzword Example from a book about Eclipse: We ll use the same mechanisms to navigate semantic errors ( ) that we use to navigate compile errors. (failing tests) semantic error is less precise than failing tests a fuzzword in this case Oxford English Dictionary: 2. a. Relating to signification or meaning. (as adjective) The ATHENA Consortium. 3 Semantics and Definitions Standard way to communicate meaning is by definition definition: Verbal description of a concept, permitting its differentiation from other concepts within a system of concepts. International Standard ISO 1087, Terminology Vocabulary, 1990 The Semantic Web is about formalizing your definitions the Semantic Web, as envisioned by Tim Berners-Lee and many others since, is a logical extension of the current Web that enables explicit [machine-processable] representations of term meanings [concepts] Frankel, David; Hayes, Pat; Kendall, Elisa; McGuinness, Deborah: MDA Journal July The ATHENA Consortium. 4

3 Formality Spectrum: formal "An ontology is an explicit and formal specification of a shared conceptualization" Ontology, e.g, OWL ontology SAPterm WordNet Informal Formal Every tomato is red. for all x ( tomato (x) implies red (x) ) The ATHENA Consortium. 5 Concept, Object, Designation (term), and Definition Object Concept Definition A one-piece, handheld phone that includes battery power and may be used without any peripheral power or antenna. (Nokia) term is verbal designation Designations (terms) Handy (DE) cellular phone, cell phone (US) (two variants) mobile (UK) The ATHENA Consortium. 6

4 More on the meaning triangle morning star evening star An example from Gottlob Frege ( ): different terms different concepts and definitions same object, the planet Venus The ATHENA Consortium. 7 Which terms are of interest? Common words/terms Shared terms Specialist terms curettage dermatologist scalpel doctor skin blade The ATHENA Consortium. 8

5 System of Concepts Structured set of concepts established according to the relations between them International Standard ISO 1087, Terminology Vocabulary Some types of relations: Hierarchic Generic (subclass, a bird is an animal) Partitive (part-whole, a tire is part of a car) Note: Superordinate and subordinate can mean any kind of hierarchic relation The ATHENA Consortium. 9 Dictionary entry versus term entry cardinal, the noun, has one entry in the American Heritage dictionary with five senses: 1. a Roman Catholic high-church official, 2. a color, 3. a bird, 4. a cloak 5. a type of number The ATHENA Consortium. 10

6 Question 1.2 How would you represent the information in this dictionary entry using concept diagrams? cardinal, the noun, has one entry in the American Heritage dictionary with five senses: 1. a Roman Catholic high-church official, 2. a color, 3. a bird, 4. a cloak 5. a type of number. Choose one answer: 2. As five concepts differentiated by context 3. As five concepts differentiated by subject field 4. As one concept The ATHENA Consortium. 11 Answer 1.2 The correct answer is two. cardinal, the noun, has one entry in the American Heritage dictionary with five senses: 1. a Roman Catholic high-church official, 2. a color, 3. a bird, 4. a cloak 5. a type of number. Cardinal Language: EN Country: US (ornithology) FIVE HOMONYMS Cardinal Language: EN Country: US Cardinal Language: EN Country: US Cardinal Language: EN Country: US Cardinal Language: EN Country: US (catholic church) (colors) (textiles) (mathematics) The ATHENA Consortium. 12

7 Definitions are historical statements heat is a form of ENERGY, viz. the kinetic and potential energy of the invisible molecules of bodies OED 2nd edition heat is an elastic material fluid of extreme subtlety attracted and absorbed by all bodies (OED, same entry as previous definition) heat? heat The ATHENA Consortium. 13 Definition is Social Find and use the standardized terminology as decided by experts in the subject field Discuss in your product development and information development teams how to: Find the standards and authorities Build up team libraries (textbooks, glossaries, journals, articles ) Distribute lists of useful links Meet experts at conferences Social aspects language community research brain storming review consensus and, perhaps, create standard terminology for the industry based on new concepts and products The ATHENA Consortium. 14

8 Summary: Writing Definitions Strategies for writing definitions Identify and list distinguishing characteristics, intension Use them to write definition Use system of concepts Genus (super-class) and difference Things to keep in mind Social awareness Purpose and audience Choice of terms Include illustrations of use Include example data for data element definitions The ATHENA Consortium. 15 Graphic representation of necessity and sufficiency super-class subclass equivalent The ATHENA Consortium. 16

9 Possible relationships between two classes super-class subclass equivalent overlapping disjoint complement The ATHENA Consortium. 17 Ontologies Ontologies are about vocabularies and their meanings, with explicit, expressive, and well-defined semantics possibly machine-interpretable. By machine-interpretable we mean that the semantics of the model is semantically interpretable by the machine; in other words, the computer and its software can interpret the semantics of the model directly without direct human involvement. The standard definition for ontologies is A formal, explicit specification of a shared conceptionalization The ATHENA Consortium. 18

10 Ontologies According to T. Berners-Lee, J. Hendler, and O. Lassila, an ontology is a taxonomy combined with inference rules. Roughly speaking, an ontology is, for a domain, a set of classes and their relationships. An ontology is represented in a knowledge representation language (such as a Semantic Web language like RDF/S, DAML+OIL, OWL, or in an ontology language that predates the Semantic Web, such as Ontolingua/KIF/Common Logic, OKBC, CycL, or Prolog). Ontologies provide a basis for semantic interoperability The ATHENA Consortium. 19 Ontologies A complete ontology includes the same kinds of concepts: Classes (general things) in the many domains of interest Instances (particular things) The relationships among those things The properties (and property values) of those things The functions of and processes involving those things Constraints on and rules involving those things The ATHENA Consortium. 20

11 Ontologies What does an ontology look like? André Breton Class Writer extends Person Name: String Nacionality: Country Birthdate: Date Deathdate: Date Movement: LiteraryMovement Works: Book (multiplicity n) Class Book extends Work Title: String Author: Writer Nadja Surrealism Class LiteraryMovement Name: String Writers: Writer (multiplicity n) The ATHENA Consortium. 21 Logic and proofs Logic is the discipline that studies the principles of reasoning Formal languages for expressing knowledge Well-understood formal semantics Declarative knowledge: we describe what holds without caring about how it can be deduced Automated reasoners can deduce (infer) conclusions from the given knowledge The ATHENA Consortium. 22

12 Logic and proofs An inference example Forall x (Person(x) => Mortal(x) So if Person(Socrates) (Socrates is a person), therefore, Mortal (Socrates) (unfortunately, Socrates is a mortal). This inference is correct because Forall x (Person(x) => Mortal(x) is a First-Order Logic expression, and because FOL has a formal semantics and syntaxis. Logical languages Inferences can be proof The ATHENA Consortium. 23