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  1. Semantic Web Andrejs Lesovskis

  2. Agenda Syntax and semantics Introduction to Semantic Web Semantic Web layers Projects that use Semantic Web technologies

  3. Syntax and semantics (1) • A term for the study of the rules governing the way words are combined to form sentences in a language. • In computer science it refers to the ways symbols may be combined to create well-formed programs in the language. • It defines the formal relations between the constituents of a language.

  4. Syntax and semantics (2) • Semantics is the study of the meaning of linguistic expressions. The language can be a natural language, such as English or Navajo, or an artificial language, like a computer programming language. • Natural-language semantics is important in trying to make computers better able to deal directly with human languages.

  5. What is Semantic Web? "The Semantic Web is not a separate Web but an extension of the current one (World Wide Web – WWW), in which information is given well-defined meaning, better enabling computers and people to work in cooperation. ... a web of data that can be processed directly and indirectly by machines." TimBerners-Lee,JamesHendler, andOraLassila.

  6. Semantic Web and World Wide Web

  7. Semantic Web and World Wide Web applications agents

  8. Resource Integration Semantic annotations Shared ontology Web resources, services, databases 8 8

  9. Resource integration Industrial and business processes External resources Web resources, services, databases Web users Shared ontology Multimedia resources Web agents/applications Mobile devices Machines and devices 9

  10. Semantic Web and semantic network (1)

  11. Semantic Web and semantic network (2)

  12. Semantic Web inventor Semantic web inventor SirTimothyBerners-Leebest known as the inventor of the World Wide Web. Berners-Lee is the director of the World Wide Web Consortium (W3C), which oversees the Web's continued development.

  13. Semantic Web layers (1)

  14. Semantic Web layers (2) • URI and Unicode • XML (eXtensible Markup Language) • RDF (Resource Derscription Framework) • Ontology • Logic • Proof • Trust • User interface and applications

  15. Semantic Web layers (3)

  16. XML and Semantic Web Standards Timeline

  17. Project OpenCalais (Thomson Reuters) • Thomson Reuters launched project Calais in January 2008. • Calais Web Service processes unstructured text (like news articles, blog postings, scientific papers, etc.) and it returns semantic metadata in RDF format. • Uses natural language processing and machine learning techniques to examine the text and locate the entities, facts, and events.

  18. Swoogle search engine

  19. Project DBPedia.org (1) • DBpedia is a project aimed to extract structured content from the information created as part of the Wikipedia project ("infobox" tables). This structured information is then made available on the World Wide Web. • The DBpedia knowledge base allows users to query relationships and properties associated with the Wikipedia resources, including links to other related datasets. • Used technologies: Scala, Java, VirtuosoUniversal Server.

  20. Project DBPedia.org (2)

  21. Project DBPedia.org (3)

  22. Project DBPedia.org (4) DBPedia project results: • Data extraction from 97 languages, • English version of the DBpedia knowledge base currently describes 3.77 million things, including 764,000 persons, 573,000 places, 333,000 creative works, 192,000 organizations, 202,000 species and 5,500 diseases., • Contains more than 672 million RDF triples, • Tests show 87% precision, • Developed a large multi-domain ontology.

  23. RDF Site Summary (RSS) RSS (Really Simple Syndication)is a family of web feed formats used to publish frequently updated works — such as blog entries, news headlines, audio, and video — in a standardized format.

  24. Really Simple Syndication (RSS) <?xml version="1.0" encoding="UTF-8" ?> <rss version="2.0"> <channel> <title>RSS Title</title> <description>This is an example of an RSS feed</description> <link>http://www.someexamplerssdomain.com/main.html</link> <lastBuildDate>Mon, 06 Sep 2010 00:01:00 +0000 </lastBuildDate> <pubDate>Mon, 06 Sep 2009 16:45:00 +0000 </pubDate> <ttl>1800</ttl> <item> <title>Example entry</title> <description>Here is some text containing an interesting description.</description> <link>http://www.wikipedia.org/</link> <guid>unique string per item</guid> <pubDate>Mon, 06 Sep 2009 16:45:00 +0000 </pubDate> </item> </channel> </rss>

  25. URI un Unicode • Unicode- is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems. • URI (UniformResourceIdentifier) • URL(UniformResourceLocator) • http://www.google.com • mailto:email@example.com • URN(UniformResourceName) • URN of "Spider-Man"movie: urn:isan:0000-0000-9E59-0000-O-0000-0000-2 • URN of "ScienceofComputerProgramming“ magazine:urn:issn:0167-6423

  26. XML (1) XML (eXtensible Markup Language) is a markup language that defines a set of rules for encoding documents in a format that is both human-readable and machine-readable Uses tags for markup : <tag_name>data</tag_name> Some of the XML-based languages: • Extensible Hypertext Markup Language (XHTML), • Really Simple Syndication (RSS), • Mathematical Markup Language (MathML), • GraphML, • Scalable Vector Graphics (SVG).

  27. XML (2) Example: <CATALOG> <CD> <TITLE></TITLE> <ARTIST></ARTIST> <COUNTRY></COUNTRY> <COMPANY></COMPANY> <YEAR></YEAR> </CD> </CATALOG> … <breakfast_menu> <food> <name>Belgian Waffles</name> <price>$5.95</price> <description> two of our famous Belgian Waffles with plenty of real maple syrup </description> <calories>650</calories> </food> </breakfast_menu>

  28. Scalable Vector Graphics (SVG)

  29. Scalable Vector Graphics (SVG)

  30. Simple Object Access Protocol (SOAP) • SOAP Version 1.2 (SOAP) is a lightweight protocol intended for exchanging structured information in a decentralized, distributed environment. It uses XML technologies to define an extensible messaging framework providing a message construct that can be exchanged over a variety of underlying protocols. • SOAP 1.2 became a W3C recommendation in 2007.

  31. SOAP envelope

  32. SOAP example POST /InStock HTTP/1.1 Host: www.example.org Content-Type: application/soap+xml; charset=utf-8 Content-Length: 299 SOAPAction: "http://www.w3.org/2003/05/soap-envelope" <?xml version="1.0"?> <soap:Envelope xmlns:soap="http://www.w3.org/2003/05/soap-envelope"> <soap:Header> </soap:Header> <soap:Body> <m:GetStockPrice xmlns:m="http://www.example.org/stock"> <m:StockName>IBM</m:StockName> </m:GetStockPrice> </soap:Body> </soap:Envelope>

  33. Web Services Description Language (WSDL) • Web Services Description Language is an XML-based interface description language that is used for describing the functionality offered by a web service. • A WSDL description of a web service (also referred to as a WSDL file) provides a machine-readable description of how the service can be called, what parameters it expects, and what data structures it returns. • WSDL 2.0 became a W3C recommendation on June 2007.

  34. Web Services Description Language (WSDL)

  35. Semantic Web service architecture

  36. Simple Semantic Web Architecture and Protocol

  37. Simple Semantic Web Architecture and Protocol (2) The SSWAP architecture is based on the following five basic concepts: • Provider– corresponds to the organizations that own and publish resources; • Resource –arbitrary resources (for example, web pages, ontologies, or datasets), but they are primarily used to describe web services; • Graph– concept that describes transformations performed by the service; • Subject– input data that is given to the service; • Object– service execution result.

  38. Document Type Definition (DTD) Document Type Definition (DTD) is a set of markup declarations that define a document type for an SGML-family markup language (SGML, XML, HTML). DTD is a part of XML 1.0 specification. Example: DTD <?xml version="1.0"?> <!DOCTYPE bookstore [ <!ELEMENT bookstore (name,topic+)> <!ELEMENT topic (name,book*)> <!ELEMENT name (#PCDATA)> <!ELEMENT book (title,author)> <!ELEMENT title (#PCDATA)> <!ELEMENT author (#PCDATA)> <!ELEMENT isbn (#PCDATA)> <!ATTLIST book isbn CDATA "0“> ]> XML <bookstore> <name>Mike's Store</name> <topic> <name>XML</name> <book isbn=“111-111-111"> <title>XML in Nutshell</title> <author>John Smith</author> </book> </topic> </bookstore>

  39. DTD elements • External DTD declaration: <!DOCTYPE doc_elem SYSTEM/PUBLIC dtd_addr> • <!DOCTYPE chapter SYSTEM "../dtds/chapter.dtd"> • <!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML//EN" "../dtds/chapter.dtd"> • Element type declaration <!ELEMENT namecontent_model> • Any content: <!ELEMENT description ANY> • Children elements: <!ELEMENT name (first_name, last_name) > • Parsedcharacterdata: <!ELEMENT first_name (#PCDATA) > • Empty (has no content): <!ELEMENT pays_on_timeEMPTY >

  40. DTD quantifiers <?xmlversion = "1.0" standalone ="yes" ?> <!DOCTYPE document [ <!ELEMENT document (product | customer)+ > <!ELEMENT product (company, info*)+> <!ELEMENT company (#PCDATA) > <!ELEMENT info (#PCDATA) > <!ELEMENT customer (first_name, last_name) > <!ELEMENT first_name (#PCDATA) > <!ELEMENT last_name (#PCDATA) > ]> <document> <product> <company>Microsoft</company> </product> </document> Use of quantifiers • a+ • a* • a? • a, b • a | b

  41. DTDattributes • Attribute declaration template: <ATTLIST element_name attribute_nametypedefault_value ... attribute_nametypedefault_value> • Example: <ATTLIST customer type (good | bad) "good" language CDATA #FIXED "EN“> ... <customertype="good">

  42. XML Schema XML Schema 1.0 was approved as a W3C Recommendation in 2001 and it was the first separate schema language for XML to receive this status. Schema is an abstract collection of metadata, that includes the following components: element and attribute declarations and complex and simple type definitions. Schema definition example: <?xml version="1.0" encoding="utf-8"?> <xs:schema elementFormDefault="qualified" xmlns:xs="http://www.w3.org/2001/XMLSchema"> <xs:element name="ElementName"> ... </xs:element> </xs:schema> Reference to an XL Schema: <?xml version="1.0" encoding="utf-8"?> <ElementName xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="SimpleAddress.xsd“> ... </ElementName>

  43. XML Schemaexample <?xml version="1.0“?> <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <xsd:element name="employee" type="fullpersoninfo"/> <xsd:complexType name="personinfo"> <xsd:sequence> <xsd:element name="firstname" type="xsd:string"/> <xsd:element name="lastname" type="xsd:string"/> </xsd:sequence> </xsd:complexType> <xsd:complexType name="fullpersoninfo"> <xsd:complexContent> <xsd:extension base="personinfo"> <xsd:sequence> <xsd:element name="address" type="xsd:string"/> <xsd:element name="city" type="xsd:string"/> <xsd:element name="country" type="xsd:string"/> </xsd:sequence> </xsd:extension> </xsd:complexContent> </xsd:complexType>

  44. XML Schema elements • Simple elements don’t contain child elements or attributes: <xsd:element name="note“ type=“xsd:string> corresponds to <note>some text</note>. • Complex elements can contain child elements and/or attributes: <xsd:complexType name="fullpersoninfo"> <xsd:complexContent> <xsd:extension base="personinfo"> <xsd:sequence> <xsd:element name="address" type="xsd:string"/> …

  45. Element types • Derived types • normalizedString, • token, • language, • NMTOKEN, NMTOKENS, • Name, NCName, • ID, IDREF, IDREFS, • ENTITY, ENTITIES, • integer, • nonPositiveInteger, • negativeInteger, • long, int, short, byte, • unsignedLong, • unsignedInt, • unsignedShort, • unsignedByte. • Primitive types • string, • boolean, • decimal, • float, • double, • duration, • dateTime, time, date, • gYearMonth, gYear, • gMonthDay, gDay, • gMonth, • hexBinary, base64Binary, • anyURI, • Qname, • NOTATION.

  46. Element occurrence indicators The minOccurs indicator specifies the minimum number of times an element can occur. If minOccurs is equal to 0, then element is optional. <xs:element name="elem_name" type="xs:string“ minOccurs="0"/> The <maxOccurs> indicator specifies the maximum number of times an element can occur. If maxOccurs equals "unbounded", then element is allowed to appear an unlimited number of times. <xs:element name="elem_name" type="xs:string" maxOccurs="10" minOccurs="0"/>

  47. XML Schema attributes • Attribute declaration template: <xsd:attribute name="att_name" type="xsd:att_type" use=""> • Example: <xsd:attribute name="phone" type="xsd:string"> ... <customerphone="111-1111111">

  48. DTD vs XML Schema (1) DTD pros • It's been around longer than XML Schema; • Is a part of XML 1.0 specifications. DTD cons • Uses different from XML syntax; • Doesn’t support namespaces; • Limited number of types; • DTD describes whole document.

  49. DTD un XML Schema (2) XML Schema pros • Uses XML syntax (schemas themselves are XML documents); • Supports more data types and allows to define your own types; • Schema can define portions of the document. XML Schema cons • Pretty much none these days.

  50. Thank you!