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Semantic Web Semantic Web Andrejs Lesovskis Andrejs Lesovskis
Semantic WebSemantic Web
Andrejs LesovskisAndrejs Lesovskis
Agenda
Syntax and semanticsIntroduction to Semantic WebSemantic Web layersProjects that use Semantic Web technologies
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.
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.
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."
Tim Berners-Lee, James Hendler, and Ora Lassila.
Semantic Web and World Wide Web
Semantic Web and World Wide Web
Semantic Annotations
Ontologies Logical Support
Languages Tools Applications / Services
Web content
Users Creators WWW and Beyond
Semantic Web
Semantic Web content
Users Semantic Web and Beyond
Creators applications
agents
Resource Integration
8 8
Shared
ontology
Web resources,
services, databases
Semantic annotations
Resource integration
9
Web resources,services, databases
Shared ontology
Webusers
Mobile devices
Web agents/applications
External resources
Machines and devices
Industrial and business processes
Multimedia resources
Semantic Web and semantic network (1)
Semantic Web and semantic network (2)
Semantic Web inventorSemantic web inventor Sir Timothy Berners-Lee best 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.
Semantic Web layers (1)
Semantic Web layers (2)
URI and Unicode
XML (eXtensible Markup Language)
RDF (Resource Derscription Framework)
Ontology
Logic
Proof
Trust
User interface and applications
Semantic Web layers (3)
XML and Semantic Web Standards Timeline
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.
Swoogle search engine
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, Virtuoso Universal Server.
Project DBPedia.org (2)
Project DBPedia.org (3)
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.
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.
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>
URI un UnicodeUnicode - is a computing industry standard for the consistent encoding, representation and handling of text expressed in most of the world's writing systems.
URI (Uniform Resource Identifier)URL (Uniform Resource Locator)
http://www.google.com
mailto:[email protected]
URN (Uniform Resource Name)URN of "Spider-Man" movie: urn:isan:0000-0000-9E59-0000-O-0000-0000-2
URN of "Science of Computer Programming“ magazine:urn:issn:0167-6423
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-readableUses 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).
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>
Scalable Vector Graphics (SVG)
Scalable Vector Graphics (SVG)
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.
SOAP envelope
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>
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.
Web Services Description Language (WSDL)
Semantic Web service architecture
Simple Semantic Web Architecture and Protocol
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.
Document Type Definition (DTD)
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>
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 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 name content_model> • Any content: <!ELEMENT description ANY>
• Children elements: <!ELEMENT name (first_name, last_name) >
• Parsed character data: <!ELEMENT first_name (#PCDATA) >
• Empty (has no content): <!ELEMENT pays_on_time EMPTY >
DTD quantifiers
Use of quantifiers• a+• a*• a?• a, b• a | b
<?xml version = "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>
DTD attributes Attribute declaration template:
<ATTLIST element_name
attribute_name type default_value
...
attribute_name type default_value>
Example:
<ATTLIST customer
type (good | bad) "good"
language CDATA #FIXED "EN“>
...
<customer type="good">
XML SchemaXML 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>
XML Schema example<?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>
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"/>
…
Element typesPrimitive types string, boolean, decimal, float, double, duration, dateTime, time, date, gYearMonth, gYear, gMonthDay, gDay, gMonth, hexBinary, base64Binary, anyURI, Qname, NOTATION.
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.
Element occurrence indicatorsThe 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"/>
XML Schema attributes
Attribute declaration template:
<xsd:attribute name="att_name" type="xsd:att_type" use="">
Example:
<xsd:attribute name="phone" type="xsd:string">
...
<customer phone="111-1111111">
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.
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.
Thank you!Thank you!
