ontology engineering: introduction

Welcome to Ontology Engineering

Guus Schreiber

Agenda • Course introduc:on: what is an ontology? • Administra:on

• RDF/RDFS

Lecture 1

Literature

• James Odell, Ontology White Paper, CSC Catalyst, 2011, V2011-‐07-‐15,

hNp://www.jamesodell.com/Ontology_White_Paper_2011-‐07-‐15.pdf.

• For this lecture Sec.s 1-‐4 are relevant

• Acknowledgement: some figures in this lecture come from the paper above.

What is an Ontology?

• In philosophy: theory of what exists in the world • In IT: consensual & formal descrip:on of shared concepts in a domain • Aid to human communica:on and shared understanding, by specifying meaning

• Machine-‐processable (e.g., agents use ontologies in communica:on)

• Key technology in seman:c informa:on processing • Applica:ons: knowledge management, e-‐business, seman:c world-‐wide web.

What is an Ontology? II

“explicit specifica-on of a shared conceptualiza-on that holds in a par-cular

context” (several authors)

Knowledge sharing and reuse

• Knowledge engineering is costly and :me-‐consuming

• Distributed systems

• Increasing need for defini:on of a common frame of reference – Internet search, document indexing, ….

Need for data integra:on?

Seman:c Web

• Data integra:on • AAA slogan • Non-‐Unique Naming Assump:on

• Open vs. closed World

The Web: resources and links

URL URL

Web link

The Seman:c Web: typed resources and links

URL URL

Web link

ULAN

Henri Ma:sse

Dublin Core

creator

Pain:ng “Woman with hat SFMOMA

Seman:c Web

WordNet

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Domain standards and vocabularies as ontologies

• Contain ontological informa:on • Ontology needs to be “extracted”

– Not explicit • Lists of domain terms are some:mes also called “ontologies” – Implies a weaker no:on of ontology – Scope typically much broader than a specific applica:on domain

– Contain some meta informa:on: hyponyms, synonyms, text

• Structured knowledge is available (on the web) – use it!

Ontology spectrum

Source: http://www.jamesodell.com/Ontology_White_Paper_2011-07-15.pdf.

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Document fragment ontologies

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Instruc:onal document fragment ontologies

Context and Domain

Principle 1: “The representa:on of real-‐world objects always depends

on the context in which the object is used. This context can be seen as a “viewpoint” taken on the object. It is usually impossible to enumerate in advance all the possible useful viewpoints on (a class of ) objects.”

Principle 2: “Reuse of some piece of informa:on requires an explicit

descrip:on of the viewpoints that are inherently present in the informa:on. Otherwise, there is no way of knowing whether, and why this piece of informa:on is applicable in a new applica:on seing.”

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Mul:ple views on a domain

• typical viewpoints captured in ontologies: • func:on • behavior, • causality • shape, geometry • structure: part-‐of (mereology), aggrega:on • connectedness (topology)

• viewpoints can have different abstrac:on (generaliza:on) levels

• viewpoints can overlap • applica:ons require combina:ons of viewpoints

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Mul:ple views on a domain

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Context specifica:on through ontology types

• Domain-‐specific ontologies – Medicine: UMLS, SNOMED, Galen – Art history: AAT, ULAN – STEP applica:on protocols

• Task-‐specific ontologies – Classifica:on – E-‐commerce

• Generic ontologies – Top-‐level categories – Units and dimensions

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Top-‐level categories: many different proposals

Chandrasekaran et al. (1999)

The famous is-‐a rela:onship


Classes as instances

24 Source: http://www.jamesodell.com/Ontology_White_Paper_2011-07-15.pdf.

What is an Ontology?

“explicit specifica-on of a shared conceptualiza-on that holds in a par-cular

context” (several authors)

Concepts

• Help us organize the world around us • Act as recogni:on device • Test for reality • We use many different types of concepts

Concept types


The concept triad


Concept specifica:on

• Symbol – Name used for the concept – Can be different names, different languages – E.g., “bike”, fiets”

• Intension (defini:on) – Intended meaning of the concept (seman:cs) – E.g. a bike has at least one wheel and a human-‐powered movement mechanism

• Extension – Set of examples of the concept – E.g. “my bike”, “your bike”

Incomplete concept specifica:ons

• Are common • Think of an example:

– Concept with no instances – Concept with no symbol

• Primi:ve vs. defined concepts

Domain = area of interest

• Can be any size – e.g., medicine

• Concepts may have different symbols in different domains

• The same symbol may be used for different concepts in different domains (some:mes also in the same domain)

Ontology Specifica:on

• Aggrega:on • Rela:on-‐aNribute dis:nc:on • Trea:ng rela:ons as classes • Sloppy class/instance

dis:nc:on – Class-‐level aNributes/rela:ons

– Meta classes • Constraints • Data types • Modularity

– Import/export of an ontology

• Ontology mapping

• Class (concept) • Subclass with inheritance • Rela:on (slot)

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Ontology Languages

– UML – RDF Schema, OWL – …..

• Common basis – Class (concept) – Subclass with inheritance – Rela:on (slot)

Ontology Tools

Best known tool • Protégé (Stanford) • We will use this tool

Decision points: – Expressivity – Graphical representa:on – DB backend – Modulariza:on support – Versioning

Administra:on

• Course website: hNp://seman:cweb.cs.vu.nl/OE2012/

• Use blog posts for content ques:ons • Use oe-‐[email protected] for admin ques:ons

Engineering needs prac:ce!

Lots of exercises throughout the course: • Two mee:ngs per week

• Lectures on Monday

• Work sessions on Thursday

• You are encouraged to do assignments together with colleagues

• Individual porsolio

RDF(S) Recap

• Which RDF/RDF-‐Schema constructs do you remember?

URIs, URLs

• URI: global iden:fier for a web resource • hNp://www.w3.org/2006/03/wn/wn20/instances/synset-‐anniversary-‐noun-‐1

• URL: dereferencable URI, used to locate a file on the web.

• hNp://www.w3.org/2006/03/wn/wn20/instances/synset-‐anniversary-‐noun-‐1

• URI abbrevia:ons: – Qnames

• Namespace:iden:fier • Wordnet:synset-‐anniversary-‐noun-‐1

Triples

ulan:Shakespeare ulan:parentOf ulan:Susanna.

kb:Hamlet kb:author kb:Shakspeare.

ex:VrijeUniversiteit ex:locatedIn tgn:Amsterdam.

ex:WillemHage ex:teaches ex:OntologyEngineering.

ex:OntologyEngineering rdf:type ex:Course.

Syntax

• N3 Turtle – hNp://www.w3.org/TeamSubmission/turtle/

• RDFXML – hNp://www.w3.org/TR/rdf-‐syntax-‐grammar/

Blank nodes

How would you model “Sonnet78 was inspired by a woman who lives in England”?

Lit:Sonnet78 lit:hasInspiration [ rdf:type bio:Woman; bio:livedIn geo:England ] .

subClassOf

IF A rdfs:subClassOf B r rdf:type A

THEN r rdf:type B

subPropertyOf

IF P rdfs:subPropertyOf R a P b

THEN a R b

Domain and Range

IF P rdfs:domain D x P y

THEN x rdf:type D

IF P rdfs:range R x P y

THEN y rdf:type R

More RDF(S)

• rdfs:label • rdfs:comment

• rdfs:seeAlso

RDF-‐Schema

• Provides a way to talk about the vocabulary – Define classes, proper:es

bb:author rdf:type rdfs:Property • Enables inferencing

– Inferring new triples from asserted triples.

• subClassOf, subPropertyOf, domain, range.

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Guidelines for ontological engineering (1)

• Do not develop from scratch • Use exis:ng data models and domain standards as star:ng point

• Start with construc:ng an ontology of common concepts

• If many data models, start with two typical ones • Make the purpose and context of the ontology explicit – E.g. data exchange between ship designers and assessors

– Opera:onally purpose/context with use cases • Use mul:ple hierarchies to express different viewpoints on classes

• Consider trea:ng central rela:onships as classes

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Guidelines for ontological engineering (2)

• Do not confuse terms and concepts • Small ontologies are fine, as long as they meet their goal • Don’t be overly ambi:ous: complete unified models are

difficult • Ontologies represent sta:c aspects of a domain

– Do not include work flow • Use a standard representa:on format, preferably with a

possibility for graphical representa:on • Decide about the abstrac:on level of the ontology early

on in the process. – E.g., ontology only as meta model

ontology engineering: introduction

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