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Markup Languages and the Semantic Web

Lecture Notes Prepared by

Jagdish S. GangollyInterdisciplinary Ph.D Program in Information

ScienceState University of New York at Albany

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Markup Languages

• Knowledge assumed:– HTML

• DTD (Document Type Definition)

• Tags– Format (confusion between format and other tags)

– Structure (Too flexible, and so almost useless)

– Content (virtually none)

• Very poor in semantics

• Inability to exploit latent semantics

• Users at the mercy of browsers

• Inflexibility in adding new tags un less blessed by browsers

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XML I

• SGML, the forerunner of HTML– Too complex (annotated SGML standard runs over

1,000 pages– Too flexible– Little browser support

• XML– Less complex and yet extensible– Flexible in expressing semantics– Browser support

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XML II

• Separation of format, content, and structure tags– Content: Schema

• Rich set of data types

• Easy to understand and implement

– Format: XSL (XML Style-sheet language)• Complex and no universal browser support

• Such support may not be crucial because of XSLT (XSL Transform) which enables HTMLize XML

– Structure: Subsumed in content and format– Representing richer semantics than HTML allowed

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XML III

• Discipline enforced• Document Type Definition, required to specify the

grammar of HTML and SGML required programmers to be familiar with one more language (EBNF - Extended Backus-Naur Formalism) in which DTDS are represented.

• Good browser support• DOM (Document Object Model), SAX (Simple API for

XML), and Namespaces facilitates machines to communicate and (understand) mutual data to an extent

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Semantic Web

• ..is a mesh of information linked up in such a way as to be easily processable by machines, on a global scale. (http://infomesh.net/2001/swintro/)

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Motivation

• Need for interchangeability of information (information sharing)

• Need for interchangeability, translatability, uniformity of ontologies

• Need for improving precision in retrieval

• Need for web services based on understanding of data as well as metadata

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Semantic Web Components

– Data• Structure• Content• Format• Ontology

– Metadata• Representation Languages• Facility for metadata Interchange

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Data

• Data (Semi-structured as well as structured)

•Structure Tags: XML-Schema

•Content Tags: XML-Schema

•Ontology: Ontology representation languages

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Metadata I

• Representation languages based on First Order Logic

• KIF-based Ontolingua (http://www.ksl.stanford.edu/software/ontolingua/

• Loom (http://www.isi.edu/isd/LOOM/LOOM-HOME.html)

• Frame-Logic (http://www.cs.sunysb.edu/~kifer/dood/papers.html)

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Metadata II

• Languages using standardised syntax– Simple HTML Ontology Extensions (SHOE) (

http://www.cs.umd.edu/projects/plus/SHOE/)– XOL Ontology Exchange Language (XOL)(

http://www.ai.sri.com/pkarp/xol/)– Ontology Markup Language (OML and CKML)

(Ontology Markup Language (OML and CKML) – Resource Description Framework Schema

Language (RDFS) (http://www.w3.org/TR/rdf-schema/)

– RiboWEB (http://www-smi.stanford.edu/projects/helix/riboweb/kb-pub.html)

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Metadata III

– OIL (Ontology Interchange Language) (http://www.ontoknowledge.org/oil/)

– DAML+OIL (http://www.daml.org)– XFML+CAMEL (eXchangeable Faceted Metadata

Language + Compound term composition Algebraically-Motivated Expression Language) (http://www.csi.forth.gr/~tzitzik/XFML+CAMEL/)

• Good sources of information: – http://www.cs.umd.edu/users/hendler/sciam/

walkthru.html– http://www.w3.org/2001/sw/

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Dublin Core

• Metadata ElementsISO 15836:2003

Title Format

Creator Identifier

Subject Source

Description Language

Publisher Relation

Contributor Coverage

Date Rights

Type

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RDF (http://www.xml.com/pub/a/2002/01/30/daml1.html)

• XML based language that allows you to define classes and properties<rdfs:Class rdf:ID="Product">

<rdfs:label>Product</rdfs:label> <rdfs:comment>An item sold by Super Sports Inc.</rdfs:comment> </rdfs:Class>

<rdfs:Property rdf:ID="productNumber"> <rdfs:label>Product Number</rdfs:label> <rdfs:domain rdf:resource="#Product"/> <rdfs:range rdf:resource="http://www.w3.org/2000/01/rdf-schema#Literal"/> </rdfs:Property>

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RDF

• "there is a Person identified by http://www.w3.org/People/EM/contact#me, whose name is Eric Miller, whose email address is em@w3.org, and whose title is Dr."

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RDF

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RDF

<?xml version="1.0"?><rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"

xmlns:contact="http://www.w3.org/2000/10/swap/pim/contact#">

<contact:Person rdf:about="http://www.w3.org/People/EM/contact#me">

<contact:fullName>Eric Miller</contact:fullName> <contact:mailbox rdf:resource="mailto:em@w3.org"/> <contact:personalTitle>Dr.</contact:personalTitle> </contact:Person>

</rdf:RDF>

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DAML+OIL I (http://www.xml.com/pub/a/2002/01/30/daml1.html)

• DAML+OIL also allows you to define instances of classes and specify their properties<Product rdf:ID="WaterBottle"> <rdfs:label>Water Bottle</rdfs:label> <productNumber>38267</productNumber> </Product>

• DAML+OIL allows datatyping<daml:DatatypeProperty rdf:ID="productNumber"> <rdfs:label>Product Number</rdfs:label> <rdfs:domain rdf:resource="#Product"/> <rdfs:range rdf:resource="http://www.w3.org/2000/10/XMLSchema#nonNegativeInteger"/> </daml:DatatypeProperty>

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DAML+OIL II

• Provides for uniqueness, equivalence, enumerations, disjoint classes, disjoint unions of classes, non-exclusive Boolean combinations of classes, intersection of classes, sub-classing, property restrictions

• Rich enough to model ontologies

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Semantic Web Stack of Expressive Power (Berners-Lee)

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

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Semantic Web Stack of Expressive Power (Berners-Lee)

• URI (Uniform Resource Identifier)– http://www.ietf.org/rfc/rfc2396.txt

• Unicode – unicode.org

• XML– http://www.w3.org/XML/

• RDF– http://www.w3.org/RDF/

• RDF-S (RDF Schema)– www.w3.org/TR/2000/CR-rdf-schema-20000327/

• SPARQL– www.w3.org/TR/rdf-sparql-query/

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• OWL (Web Ontology Language)– http://www.w3.org/2004/OWL/

• RIF– http://www.w3.org/TR/rif-core/

• Unifying Logic

• Proof

• Crypto

• Trust

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Web Ontology Language (OWL) I

• OWL Lite supports those users primarily needing a classification hierarchy and simple constraints.

• OWL DL supports those users who want the maximum expressiveness while retaining computational completeness (all conclusions are guaranteed to be computed) and decidability (all computations will finish in finite time).

• OWL Full is meant for users who want maximum expressiveness and the syntactic freedom of RDF with no computational guarantees.

Source: http://www.w3.org/TR/owl-features/

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Semantic Web: Readings

• Semantic Web: Readings

• “The Semantic Web In Breadth”, by Aaron Swartz– http://logicerror.com/semanticWeb-long

• The Semantic Web: An Introduction– http://infomesh.net/2001/swintro/