Semantic Web and Web 3.0 - Lecture 9 - Web Technologies (1019888BNR)

This lecture forms part of the course Web Technologies given at the Vrije Universiteit Brussel.

Transcript

1. 2 December 2005 Web Technologies Semantic Web and Web 3.0 Prof. Beat Signer Department of Computer Science Vrije Universiteit Brussel beatsigner.com
2. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 2 November 21, 2023 The Semantic Web I have a dream for the Web [in which com- puters] become capable of analyzing all the data on the Web–the content, links, and transactions between people and computers. A 'Semantic Web', which should make this possible, has yet to emerge, but when it does, the day-to-day mechanisms of trade, bureaucracy and our daily lives will be handled by machines talking to machines. The 'intelligent agents' people have touted for ages will finally materialize. Weaving the Web - The Original Design and Ultimate Destiny of the World Wide Web by Its Inventor, Tim Berners-Lee, Harper San Francisco, September 1999 Tim Berners-Lee
3. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 3 November 21, 2023 The Semantic Web ... The Semantic Web is a vision: the idea of having data on the Web defined and linked in a way that it can be used by machines not just for display purposes, but for auto- mation, integration and reuse of data across various applications. Metadata provides a means to make statements and create machine-readable statements. W3C, 2003
4. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 4 November 21, 2023 The Semantic Web ... ▪ Meaning of data on the Web can not only be inferred by people but also discovered by machines without (or with less) human intervention ▪ Web of Data instead of Web of Documents ▪ the Web as a huge decentralised database (knowledge base) ▪ machine-accessible data ▪ data may be interconnected similar to today's webpages ▪ machine-readable metadata for existing web content ▪ combination of data from different sources to derive new facts ▪ machines (agents) may use logical reasoning to infer facts that are not explicitly recorded ▪ Crucial component of Web 3.0 or Giant Global Graph
5. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 5 November 21, 2023 Video: The Future Internet
6. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 6 November 21, 2023 Semantic Web Stack ▪ The Semantic Web Stack (or Semantic Web Cake) describes the architecture of the Semantic Web ▪ URI/IRI - unique identification of semantic web resources ▪ Unicode - representing/manipulating text in different languages ▪ XML - interchange of structured data over the Web Character set: UNICODE Cryptography Syntax: XML and XML Namespaces Data interchange: RDF Taxonomies: RDFS Ontologies: OWL Querying: SPARQL Unifying Logic Trust User interface and applications Proof Rules: RIF/SWRL Based on [http://en.wikipedia.org/wiki/File:Semantic-web-stack.png] Identifiers: URI/IRI
7. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 7 November 21, 2023 Semantic Web Stack ... ▪ XML Namespaces - uniquely qualify markup from multiple sources (integration) ▪ Resource Description Framework (RDF) - define RDF triples and repre- sent resource information in a graph structure ▪ RDF Schema (RDFS) - create hierarchies of classes and properties Character set: UNICODE Cryptography Syntax: XML and XML Namespaces Data interchange: RDF Taxonomies: RDFS Ontologies: OWL Querying: SPARQL Unifying Logic Trust User interface and applications Proof Rules: RIF/SWRL Based on [http://en.wikipedia.org/wiki/File:Semantic-web-stack.png] Identifiers: URI/IRI
8. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 8 November 21, 2023 Semantic Web Stack ... ▪ Web Ontology Language (OWL) - language to define vocabularies - extends RDFS with more ad- vanced features (e.g.cardinality) - enables reasoning based on description logic ▪ SPARQL - query language to query any RDF-based data ▪ Rule Interchange Format (RIF) and Semantic Web Rule Language (SWRL) - describe relations that cannot be described in OWL Character set: UNICODE Cryptography Syntax: XML and XML Namespaces Data interchange: RDF Taxonomies: RDFS Ontologies: OWL Querying: SPARQL Unifying Logic Trust User interface and applications Proof Rules: RIF/SWRL Based on [http://en.wikipedia.org/wiki/File:Semantic-web-stack.png] Identifiers: URI/IRI
9. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 9 November 21, 2023 Semantic Web Stack ... ▪ Unifying Logic - logical reasoning (infer new facts and check consistency) ▪ Proof - explain logical reasoning steps ▪ Cryptography - protect RDF data via encryption - validate the source of facts by digitally signing RDF data ▪ Trust - authentication of sources and trustworthiness of derived facts ▪ User Interface - user interfaces for semantic web applications Character set: UNICODE Cryptography Syntax: XML and XML Namespaces Data interchange: RDF Taxonomies: RDFS Ontologies: OWL Querying: SPARQL Unifying Logic Trust User interface and applications Proof Rules: RIF/SWRL Based on [http://en.wikipedia.org/wiki/File:Semantic-web-stack.png] Identifiers: URI/IRI
10. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 10 November 21, 2023 Resource Description Framework ▪ The Resource Description Framework (RDF) has been designed to describe ▪ data and metadata about specific subjects ▪ structure of data sets ▪ relationships between bits of data ▪ An RDF statement (triple) consists of three parts ▪ subject ▪ predicate (property) ▪ object (value) {person-1, name, "Niklaus Wirth"} subject predicate object
11. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 11 November 21, 2023 Resource Description Framework ... ▪ Subjects, predicates and objects are all resources ▪ subject is either a URI reference or a blank node ▪ predicate is a URI reference defining the relationship ▪ object is either a URI reference, a literal or a blank node ▪ RDF data is often stored in relational databases or so-called triplestores such as Apache Jena (TDB) ▪ up to billions of triples
12. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 12 November 21, 2023 RDF Graph ▪ A set of RDF statements can be represented as a directed labelled graph ▪ note that in RDF we can only define statements about specific instances but not about generic concepts - RDFS/ontologies have to be used to define statements about generic concepts Beat Signer w:hasFamilyName w:hasGivenName https://wise.vub.ac.be/beat-signer
13. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 13 November 21, 2023 RDF Graph ... ▪ Anonymous resources have no explicit identifier ▪ in the example, the "office" is an anonymous resource ▪ anonymous resources are also called blank nodes or bnodes ▪ blank nodes can only be used as subjects or objects Beat Signer w:hasFamilyName w:hasGivenName http://wise.vub.ac.be w:hasDirector https://wise.vub.ac.be/beat-signer w:isMember Lode https://wise.vub.ac.be/lode-hoste Hoste w:hasFamilyName w:hasGivenName w:isColleague w:hasOffice 10F733 026293306 w:room w:phone
14. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 14 November 21, 2023 RDF Reification ▪ An RDF triple is not a resource and can therefore not become subject of another statement ▪ we have to reify the original statement - make a resource out of the statement Beat Signer w:hasFamilyName w:hasGivenName https://wise.vub.ac.be w:hasDirector w:isMember Lode Hoste w:hasGivenName rdf:subject rdf:object rdf:statement isColleague rdf:type rdf:Property 1 w:forYears w:hasFamily Name https://wise.vub.ac.be/beat-signer https://wise.vub.ac.be/lode-hoste
15. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 15 November 21, 2023 Advantages of RDF ▪ Simple ▪ Enables the combination (merging) of data from different data models ▪ not easily possible in a relational database (different schemas) ▪ The same resource can be annotated by different people ▪ resource referenced by URI ▪ separation of data and metadata ▪ Well-defined standard ▪ many tools available - triplestores, parsers, editors, frameworks, ...
16. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 16 November 21, 2023 RDF Schema (RDFS) ▪ Vocabulary description language for RDF ▪ domain vocabulary and structure ▪ Define common concepts and relationships ▪ classes (rdfs:Class) and subclasses (rdfs:subClassOf) ▪ properties and sub-properties (rdfs:subPropertyOf) ▪ domain (rdfs:domain) and range (rdfs:range) of a property ▪ rdfs:seeAlso, rdfs:isDefinedBy (utility properties) ▪ rdfs:label, rdfs:comment ▪ ... ▪ Provides the basic elements for the definition of ontologies
17. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 17 November 21, 2023 RDF Schema Example Beat Signer w:hasFamilyName w:hasGivenName Researcher https://wise.vub.ac.be/beat-signer Lode https://wise.vub.ac.be/lode-hoste Hoste w:isColleague w:hasFamilyName w:hasGivenName rdf:type rdf:type Person isColleague rdfs:Class rdf:Property rdf:type rdf:type rdfs:domain rdfs:range rdfs:subClassOf rdfs:Literal rdfs:Literal rdfs:Literal rdfs:Literal rdf:type rdf:type rdf:type rdf:type
18. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 18 November 21, 2023 Advantages of RDFS ▪ With RDFS we have a richer expressiveness (e.g.subClassOf) than with RDF ▪ Simple reasoning (e.g.type hierarchy) ▪ Many existing tools to deal with RDFS ▪ However, some things cannot be expressed; for example ▪ "a person must have a family name" ▪ "a person can have at most one family name" (cardinality) ▪ "if Beat is a colleague of Lode then Lode is a colleague of Beat" (symmetry) → these issues are addressed by the Web Ontology Language (OWL)
19. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 19 November 21, 2023 RDF(S)/XML Serialisation ▪ Syntax not so easy to learn ▪ many different ways to construct the same statement ▪ long URIs are hard to read {https://wise.vub.ac.be/beat-signer, isColleague, https://wise.vub.ac.be/lode-hoste} <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:m="https:myspace/my/1/" > <rdf:Description rdf:about="https://wise.vub.ac.be/beat-signer"> <m:isColleague rdf:resource="https://wise.vub.ac.be/lode-hoste"/> <m:hasGivenName>Beat</m:hasGivenName> ... </rdf:Description> ... </rdf:RDF>
20. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 20 November 21, 2023 RDF Notation 3 (N3) ▪ Short non-XML serialisation ▪ separate predicates with a semicolon ▪ finish subject definition with a full stop ▪ Note that the N3 notation offers more features than are necessary for RDF(S) serialisation ▪ e.g.support for RDF-based rules <https://wise.vub.ac.be/beat-signer>m:isColleague <https://wise.vub.ac.be/lode-hoste/>; ... m:hasGivenName "Beat".
21. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 21 November 21, 2023 RDF Turtle Notation ▪ Terse RDF Triple Language ▪ Subset of N3 language ▪ only describes RDF features (RDF graph model) ▪ Syntax looks similar to Notation 3 ▪ https://www.w3.org/TeamSubmission/turtle/ ▪ Many RDF frameworks (e.g.Jena) offer Turtle parser and serialisation features
22. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 22 November 21, 2023 RDF Applications ▪ Annotea project ▪ defines an RDF schema for the types of annotations that can be used to annotate webpages ▪ RSS ▪ some RSS versions use RDF(S) /XML serialisation ▪ Dublin Core ▪ widely used to describe digital media (also in standard HTML) - bibliographic metadata such a title, creator, description, ... ▪ uses RDF(S) /XML serialisation as one possible representation <head> ... <meta name="DC.Subject" content="Cross-Media, Technology, Interactive Paper, ..."/> <meta name="DC.Description" content="Beat Signer's research on ..."/> </head>
23. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 23 November 21, 2023 SPARQL Query Language ▪ RDF query language which can be used to ▪ extract information as URIs, literals, blank nodes or subgraphs ▪ SPARQL SELECT queries return variable bindings ▪ SPARQL querying relies on graph pattern matching ▪ Example ▪ get the name and mbox of all subjects that have both of these properties defined SELECT ?name ?mbox WHERE { ?x foaf:name ?name . ?x foaf:mbox ?mbox }
24. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 24 November 21, 2023 Web Ontology Language (OWL) ▪ OWL evolved from DAML+OIL ▪ DAML is the DARPA Agent Markup Language ▪ OIL stands for Ontology Inference Layer ▪ There exist 3 different OWL sublanguages (flavours) with different expressiveness ▪ OWL Full - maximum expressiveness (full language) - no computational guarantee ▪ OWL DL - maximal OWL Full subset that is still computationally decidable ▪ OWL Lite - classification hierarchy and simple constraints (limited cardinality constraints) - weakest of the three variants
25. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 25 November 21, 2023 Jena Semantic Web Framework ▪ Open source Semantic Web framework for Java ▪ create and access data from RDF graphs via an RDF API ▪ offers an OWL API ▪ data can be stored in files, databases or accessed via URLs ▪ https://jena.apache.org ▪ RDF graphs can be serialised into different formats ▪ RDF/XML ▪ Notation 3 ▪ Turtle ▪ relational database ▪ SPARQL query interface ▪ Multiple reasoners
26. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 26 November 21, 2023 Protégé ▪ Free open-source platform to create, manipulate and visualise ontologies ▪ Two modelling tools ▪ Protégé-Frames editor - build and populate frame-based ontologies - Java API for plug-ins ▪ Protégé-OWL editor - build Semantic Web ontologies
27. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 27 November 21, 2023 Friend of a Friend (FOAF) ▪ First social Semantic Web application ▪ Miller and Brickley, 2000 ▪ Describe a social network without a central database ▪ links can be followed by spiders (data mining) ▪ no unique identifier - identification by description (predicates and objects) ▪ "six degrees of separation" or "small world phenomenon" ▪ FOAFNaut browser
28. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 28 November 21, 2023 Friend of a Friend (FOAF) ▪ Personal information and connections to friends in RDF ▪ http://www.foaf-project.org <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xmlns:foaf="http://xmlns.com/foaf/0.1/"> <foaf:Person> <foaf:name>Beat Signer</foaf:name> <foaf:title>Prof.</foaf:title> <foaf:givenname>Beat</foaf:givenname> <foaf:family_name>Signer</foaf:family_name> <foaf:nick>Beat</foaf:nick> <foaf:mbox_sha1sum>ce6d419869307d57839feef6445a9d64f784eb36</foaf:mbox_sha1sum> ... <foaf:knows> <foaf:Person> <foaf:name>Moira C. Norrie</foaf:name> <foaf:mbox_sha1sum>4cb61b36a6feaa48c78acbb51fcce7cb356afdd6</foaf:mbox_sha1sum> <rdfs:seeAlso rdf:resource="http://www.globis.ethz.ch/people/norrie.rdf"> </foaf:Person> </foaf:knows> ... </foaf:Person> </rdf:RDF>
29. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 29 November 21, 2023 Semantic Wikis ▪ Use Semantic Web technologies to provide machine-processable Wiki content ▪ page content ▪ link metadata ▪ Ontology reasoning ▪ much richer query interface ▪ Existing semantic Wikis ▪ DBPedia ▪ Semantic MediaWiki ▪ ...
30. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 30 November 21, 2023 Linked Data ▪ Link different data sources (URIs) on the Web ▪ provide metadata about the resources via RDF/XML, N3, etc. ▪ provide links to resources in other data sets on the Web ▪ Linked Open Data (LOD) cloud project ▪ RDF triples from currently 1314 datasets (DBPedia, GeneID, ...) ▪ more than 100 billion triples with billions of links https://lod-cloud.net
31. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 31 November 21, 2023 Linked Open Data
32. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 32 November 21, 2023 Semantic Desktops ▪ Apply Semantic Web tech- nologies to personal infor- mation management (PIM) ▪ inter-application data sharing ▪ enhancement of limited filesystem functionality - add document metadata ▪ Examples ▪ Haystack ▪ Nepomuk Nepomuk Integration with Dolphin (KDE 4.0)
33. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 33 November 21, 2023 Microformats ▪ Add semantics to (X)HTML pages ▪ Makes use of specific (X)HTML tag attributes ▪ class and rel attributes - e.g. rel="nofollow" for search engines ▪ Specific microformats ▪ hCard: contact information ▪ hCalendar: event information ▪ hProduct: product information
34. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 34 November 21, 2023 hCard Microformat Example ▪ Some search engines (e.g.Google and Yahoo) pay attention to different types of microformats <head profile="http://www.w3.org/2006/03/hcard"> ... </head> ... <div class="vcard"> <div class="fn">Lode Hoste</div> <div class="org">Vrije Universiteit Brussel</div> <div class="tel">32 2629 3306</div> <a class="url" href="http://wise.vub.ac.be/members/lode-hoste"> http://wise.vub.ac.be/members/lode-hoste</a> </div>
35. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 35 November 21, 2023 RDF in Attributes (RDFa) ▪ Add a set of attribute extensions to (X)HTML for embedding RDF metadata ▪ Different vocabularies ▪ FOAF, video, audio, commerce, … ▪ Search engines (e.g. Yahoo and Google) process certain RDFa metadata (e.g. product information) <p xmlns:dc=http://purl.org/dc/elements/1.1/ about="http://www.amazon.com/..."> and the will to live. <span property="dc:creator">Simpson</span> dedicates the book <cite property="dc:title">Touching the Void</cite> to the... The book was published in <span property="dc:date" content="1989-12-01">December 1989</span>. </p>
36. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 36 November 21, 2023 Microdata ▪ Add machine readable metadata (semantics) to HTML5 documents in the form of key/value pairs ▪ can be used by crawlers, search engines (SEO) and browsers to provide a richer browsing experience ▪ alternative to Microformats and RDFa W3C Working Group Note <section itemscope itemtype="http://data-vocabulary.org/Person"> Hello, my name is <span itemprop="name">Beat Signer</span> and I am a <span itemprop="title">Professor</span> at the <span itemprop="affiliation">Vrije Universiteit Brussel. </span> <section itemprop="address" itemscope itemtype="http://data -vocabulary.org/Address">My address is: <span itemprop="street-address">Pleinlaan 2</span>, <span itemprop="postal-code">1050 </span> <span itemprop="locality">Brussels</span>, <span itemprop="country-name">Belgium</span>. </section> </section>
37. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 37 November 21, 2023 Exercise 9 ▪ Semantic Web
38. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 38 November 21, 2023 References ▪ Tim Berners-Lee, James Hendler and Ora Lassila, The Semantic Web, Scientific American Magazine, May 2001 ▪ https://www.scientificamerican.com/article.cfm?id=the-semantic-web ▪ The Future Internet: Service Web 3.0 ▪ https://www.youtube.com/watch?v=off08As3siM ▪ Resource Description Framework (RDF) ▪ https://www.w3.org/RDF/ ▪ Toby Segaran, Colin Evans and Jamie Taylor, Program- ming the Semantic Web: Build Flexible Applications with Graph Data, O'Reilly Media, August 2009
39. Beat Signer - Department of Computer Science - bsigner@vub.ac.be 39 November 21, 2023 References ... ▪ The Linked Open Data Cloud ▪ https://lod-cloud.net
40. 2 December 2005 Next Lecture Web Search and SEO