Semantic Web. Semantic Web: Resource Description Framework (RDF) cont. Resource Description Framework (RDF) W3C Definition:

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Semantic Web:

• ‘The Semantic Web is an extension of the current web in which information

is given well-defined meaning,

• better enabling computers and people to work in cooperation.’

• Tim Berners-Lee, James Hendler, Ora Lassila, The Semantic Web,

Scien-tific American, May 2001

WS 2004/2005, Dokumentverarbeitung, © Prof. Dr. D. Rösner; Version: 27. Januar 2005 391

Semantic Web

W3C Definition:

• The Semantic Web is the representation of data on the World Wide Web. • It is a collaborative effort led by W3C with participation from a large number

of researchers and industrial partners.

• It is based on the Resource Description Framework (RDF), which

integra-tes a variety of applications using XML for syntax and URIs for naming.

Resource Description Framework (RDF)

• an XML text format that supports resource description and metadata

app-lications . . .

• For example, RDF might let you identify people in a Web photo album

using information from a personal contact list; then your mail client could automatically start a message to those people stating that their photos are on the Web.. . .

• . . . RDF provides tools to integrate even more, to make the Web a little bit

more into a Semantic Web.

• from: XML in 10 points

(cf.http://www.w3c.org/XML/1999/XML-in-10-points)

Resource Description Framework (RDF) cont.

• Just like people need to have agreement on the meanings of the words

they employ in their communication, computers need mechanisms for agreeing on the meanings of terms in order to communicate effectively.

• Formal descriptions of terms in a certain area (shopping or

manufactu-ring, for example) are called ontologies and are a necessary part of the Semantic Web.

• RDF, ontologies, and the representation of meaning so that computers can

help people do work are all topics of the Semantic Web Activity.

• from: XML in 10 points

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Dublin Core Metadata Initiative

• The Dublin Core Metadata Initiative is an open forum engaged in the

deve-lopment of interoperable online metadata standards that support a broad range of purposes and business models.

• DCMI’s activities include consensus-driven working groups, global

work-shops, conferences, standards liaison, and educational efforts to promote widespread acceptance of metadata standards and practices.

• http://dublincore.org/

Dublin Core Metadata Initiative

Die definierten Elemente:

Title Format Creator Identifier Subject Source Description Language Publisher Relation Contributor Coverage Date Rights Type

Beispiele für Definitionen von Elementen:

Element Name: Title

• Label: Title

• Definition: A name given to the resource.

• Comment: Typically, Title will be a name by which the resource is formally

known.

cf.http://dublincore.org/documents/dces/

Beispiele für Definitionen von Elementen: cont.

Element Name: Creator

• Label: Creator

• Definition: An entity primarily responsible for making the content of the

resource.

• Comment: Examples of Creator include a person, an organization, or a

service. Typically, the name of a Creator should be used to indicate the entity.

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Beispiele für Definitionen von Elementen: cont.

Element Name: Description

• Label: Description

• Definition: An account of the content of the resource.

• Comment: Examples of Description include, but is not limited to: an

ab-stract, table of contents, reference to a graphical representation of content or a free-text account of the content.

Beispiele für Definitionen von Elementen: cont.

Element Name: Format

• Label: Format

• Definition: The physical or digital manifestation of the resource.

• Comment: Typically, Format may include the media-type or dimensions of

the resource. Format may be used to identify the software, hardware, or other equipment needed to display or operate the resource. Examples of dimensions include size and duration. Recommended best practice is to select a value from a controlled vocabulary (for example, the list of Internet Media Types [MIME] defining computer media formats).

Resource Description Framework - RDF

• Nachfolger von PICS: Platform for Internet Content Selection • RDF ist deklarativ

• mit XML werden Metadaten repräsentiert

• in Form von Aussagen über Eigenschaften und Beziehungen sog.

Resour-cen

• Resource kann alles sein, was eine URL besitzt

Resource Description Framework - RDF

• nutzt Arbeiten zur Wissensrepäsentation (z.B. semantische Netze) • Tripel in Analogie zu Subjekt, Verb und Objekt elementarer Sätze • Beispiel:

(field 5 in database A) (is a field of type) (zip code)

• URIs zur Identifikation der Elemente im Tripel

• cf. Tim Berners-Lee, James Hendler, Ora Lassila, The Semantic Web,

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Resource Description Framework - RDF

ein einfaches Beispiel:

<Description about="http://www.w3.org/Press/99Folio.pdf"> <dc:title>The W3C Folio 1999</dc:title>

<dc:creator>W3C Communications Team</dc:creator> <dc:date>1999-03-10</dc:date>

<dc:subject>Web development, World Wide Web

Consortium, Interoperability of the Web</dc:subject> </Description>

</RDF>

cf.http://www.w3c.org/Metadata/Activity.html

Resource Description Framework - RDF

Erläuterungen zum Beispiel:

• Zeile 1: eine RDF Description

• Zeile 2: als Vokabular wird Dublin Core verwendet • Zeile 3: um welche Resource handelt es sich? • . . .

Resource Description Framework - RDF

Erläuterungen zum Beispiel:

• . . .

• Zeile 4 bis 7: die eigentlichen Metadaten als RDF-Aussagen (RDF

state-ments) über die DC-Elemente

title creator date subject

• cf.http://www.w3c.org/Metadata/Activity.html

Resource Description Framework - RDF

• XML-Namespaces können bei Namenskonflikten in RDF-Vokabularen

ge-nutzt werden

• Beispiel:’address’könnte in einem Vokabular die Bedeutung

‘Ort einer Firma’

haben, in einem anderen aber für ihre

‘Adresse im Web’

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Ontology?

• ‘. . . traditionally defined as ’the science or study of being’ (Oxford English

Dictionary)

• In AI, usually attributed to (Gruber, 1993) the notion of ontology is,

essen-tially, ‘the specification of a conceptualization’

Ontology as ‘specification of a conceptualization’

. . . as ‘specification of a conceptualization’:

• that is, defined terms and relationships between them, usually in some

formal (preferably machine-readable) manner.

• as it is currently being used in ‘semantic web’ circles –that, is, as a set of

knowledge terms, including the vocabulary, the semantic interconnections and some simple rules of inference and logic, for some particular topic. ’

• cf.http://www.cs.umd.edu/ hendler/AgentWeb.html

Ontology?

From cf.http://www.cs.umd.edu/ hendler/AgentWeb.html: ‘. . . For example the ontology of cooking and cookbooks includes

• ingredients,

• how to stir and combine them,

• the difference between simmering and deep-frying, • . . .

Ontology?

ontology of cooking and cookbooks . . .

• . . .

• the expectation that the products will be eaten or drunk, • that oil is for cooking in or consuming and not for lubrication, • and so forth.’