Resource Description Framework and Ontology

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Resource Description Framework and Ontology

• Cungen Cao
• Knowledge Acquisition Sharing Group
• Institute of Computing Technology
• Chinese Academy of Sciences
• March 25, 2002

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AI Ontology
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T. Grubers Definition
An ontology is a formal explicit specification
of a shared conceptualization
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Necessary Conditions for Something to Be
Called an Ontology

• Exhaustive
• Everything must be stated
• Explicit
• Everything must be stated explicitly
• Formal
• Everything must be stated formally
• Consensual
• Everything stated is consensus

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Geographical Ontology
defcategory Basic-Entity attribute
full-name type String attribute
abbreviated-name type String attribute
informal-definition type Text attribute
formal-definition type First-Order-Formula rel
ation is-instance type Concept relation
has-part type Instance
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defcategory Location relation
in-east-of type PhysicalEntity relation
in-south-of type PhysicalEntity relation
in-west-of type PhysicalEntity relation
in-north-of type PhysicalEntity relation
in-middle-of type PhysicalEntity
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defcategory Region inherits Basic-Entity
includes Location attribute
population type Integer facet
time attribute land-area type Real unit
km2 attribute average-summer-whether type
Real unit ?
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defcategory City inherits Region relation
geographical-part-of type GeographicalEntity a
ttribute city-flower type PlantEntity
defcategory Country inherits Region attribute
capital-city type GeographicalEntity attribu
te first-regional-division type
GeographicalEntity attribute national-flower
type GeographicalEntity attribute
number-of-nationalities type Integer
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Geographical Axioms
Axiom 1. ?geographical entities X and Y,
in-east-of(X,Y) ? in-west-of(Y,X). Axiom 1?.
?geographical entities X and Y, in-east-of(X,Y) ?
in-west-of(Y,X) ? in-northwest-of (Y,X) ?
in-southwest-of (Y,X). Axiom 2. ?city X,
?country Y, geographical-part-of(X,Y) ?
population(X) ? population(Y).   Axiom 3. ?city
X ?country Y, geographical-part-of(X,Y) ?
number-of-nationalities(X) ? number-of-nationaliti
es(Y).   Axiom 4. ?city X, ?country Y,
capital-city(X,Y)?geographical-part-of(X,Y)
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Steps in Ontology Building

• Which domain?
• What purposes?
• What categories?
• What attributes for each category?
• How are categories interrelated?
• How are relationships constrained?

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Standard Universal Ontology?

• Is there any universal ontology covering
  everything?
• Most probably no!
• Every enterprise has his own preferences
• Ontology translation is a necessity

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Resource Description Framework
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Web Information Retrieval

• Agent-based Search Engines
• E.g. Altavista, Infoseek, Excite
• Brute force
• Metadata-based Search Engines
• E.g. Yahoo
• Man-generated categories subject labels

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Metadata-Based Information Retrieval

• Metadata
• Book
• Author, Title, Publisher, Date of Publication,
  Subject
• lookup information Bai Shuo, Li Guojie
• Person
• Name, Surname, First Name, Gender, Date of Birth,
  Date of Place, etc.
• Geographic Entity
• Name, Location, Population, Nationalities, etc.

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Resource Description Framework

• RDF is a common framework for representing
  metadata for Web resources between different
  applications
• RDF descriptions can be exchanged without loss of
  semantics!

A resource is anything that can have a
URI E.g. my electronic paper Ontology whose URL
is http//www.nki.net.cn/ontology.htm
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Resource Description Framework

• Resources are specified by properties
• Title, author, date of last modification, etc.
• See Dublin Core Metadata
• A property is a resource having a name, URI, and
  it own properties
• You can define your own properties!
• Properties defined by you can be searched,
  manipulated and sold like any other resource!

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Resource Description Framework

• A statement (Resource, Property, Value) or
  (Subject, Predicate, Object) is a resource
• You can define metadata for statements!

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Why Is XML Better Than RDF?

• Advantages of XML
• A device for inventing tags freely to structure
  your documents
• E.g. The company ltnamegt IBM lt/namegt

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Why Is XML Better Than RDF?

• Disadvantages of XML
• XML is a serial language, Maintaining such an
  order over Internet may not be time-consuming
• When you represent general XML documents in
  computer memory, you get weird data structures
  that mix trees, graphs, and character strings. In
  general, these are hard to handle in even
  moderate amounts, let alone by the billion

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XML Is the Foundation of RDF

• RDF relies on the support of XML, and XML syntax
  is only one possible syntax for RDF
• RDF uses XML to exchange descriptions of
  resources

RDFS
RDF
XHTML
XML
HTML
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Is RDF Enough?

• RDF itself does not have an inference engine
• the RDF data model does not provide any mechanism
  for declaring specific classes of resources, or
  for declaring which properties may be applicable
  to which classes of resources.

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We Need RDF Schemas

• A Type System
• An RDF schema defines the properties of a
  resource (title, author, subject, size, color,
  etc.)
• An RDF schema defines the types of resources
  (e.g. Web pages, animals and geographical
  entities) which the properties can be applicable.
• An RDF schema defines properties in terms of the
  classes of resource to which they apply.
• Domain and range constraints on the properties

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RDF Schemas

• RDFS Classes
• rdfs Class
• rdfs Resource
• rdf Property
• rdfsContrainstProperty
• rdfs Literal

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RDF Schemas

• RDF Properties (Instances of rdf Property)
• rdf type. (R, rdftype, C)?R is
  an instance of C
• rdfs subClassOf. (C, rdfs subClassOf,
  rdftype rdfs Class)
• rdfs subPropertyOf
• rdfs domain
• Domain constraints define the applicability of
  properties
• rdfs range
• Range constraints are only applied to properties
• Value of a range constraints is a class

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• rdfs label
• rdfs comment
• rdfs seeAlso
• rdfs isDefinedBy
• rdfs subPropertyOf rdfs seeAlso

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Discussion
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OIL Ontology Inference Layer

• An ontology infrastructure for semantic Web
• Vrije, Manchester, Stanford, Bell lab,
• Frame Formalism Description Logic
• For OIL ontology semantics
• Ontology design reasoning support
• (FaCT by Manchester)

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OIL Layered Architecture

• Core OIL
• Compatible with RDFS
• Standard OIL
• Heavy OIL

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Gene Ontology

• GO (Gene Ontology) is a controlled vocabulary
  used to describe the biology of a gene product in
  any organism.
• A gene product has one or many molecular
  functions
• A gene product may be used in one or many
  biological processes
• A gene product may appear in several cellular
  component

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Gene Ontology

• Purpose Common Language for Annotating Gene
  Products
• Useful Internet Resources
• http//www.geneontology.com/
• http//genome-www.stanford.edu/GO
• http//www.ebi.ac.uk/interpro/QuickGo

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Gene Ontology

• GO has 3 independent ontologies in DAG
• molecular function describes tasks done by gene
  products at molecular level
• biological process describes broad biological
  goals accomplished by ordered assemblies of
  molecular functions
• cellular component describes subcellular
  structures, locations, and macromolecular
  complexes

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GO Process Ontology