Semantic Web: an introduction

Short seminar about the Semantic Web, given for the "Artificial Intelligence" course at Politecnico di Torino (academic year 2013/2014)

Transcript

1. THE SEMANTIC WEB AN INTRODUCTION LUIGI DE RUSSIS
2. THE WEB IS A WEB OF DOCUMENT FOR PEOPLE, NOT FOR MACHINES
3. THE WEB IS A WEB OF DOCUMENT
4. THE SEMANTIC WEB IS A WEB OF DATA Linking Open Data cloud diagram, by Richard Cyganiak and Anja Jentzsch. http://lod-cloud.net/
5. LET’S THINK!
6. HOW TO GET DATA FROM THE WEB?
7. HOW TO GET DATA FROM THE WEB? DATA IS PRESENT ON SOME WEBSITES Wikipedia, GitHub, Twitter, Facebook, … HOW TO GET IT? different, evolving and proprietary Web APIs various data exchange formats
8. EXAMPLE GITHUB Web APIs (third version) https://developer.github.com/v3 Data available in JSON Authentication is required for most calls
9. EXAMPLE TWITTER https://dev.twitter.com/docs/ Authentication is required for most calls Limitations about number of requests Data available in JSON RESTful Web APIs (version 1.1) Streaming APIs (version 1.1)
10. EXAMPLE WIKIPEDIA MediaWiki Web APIs (version 1.1) http://www.mediawiki.org/wiki/API:Main_page Data available in JSON, PHP, WDDX, XML, YAML, TXT, … RSS Direct XML exports
11. HOW TO GET DATA FROM THE WEB? DATA IS LOCKED IN “DATA ISLANDS” Wikipedia, GitHub, Twitter, Facebook, … LIMITED OR NO ACCESS TO THIS DATA different, evolving and proprietary Web APIs various data exchange formats
12. DATA ON THE WEB IS NOT ENOUGH! we need a proper infrastructure DATA SHOULD BE AVAILABLE ON THE WEB accessible and structured via standard Web technologies not controlled by applications, only DATA SHOULD BE INTERLINKED OVER THE WEB i.e., data can be integrated over the Web THIS IS WHERE SEMANTIC WEB COME IN
13. DEFINITIONS
14. To a computer, the Web is a flat, boring world, devoid of meaning. This is a pity, as in fact documents on the Web describe real objects and imaginary concepts. […] Adding semantics to the Web involves two things: allowing documents which have information in machine-readable forms, and allowing links to be created with relationship values. Only when we have this extra level of semantics we will be able to use computer power to help us exploit the information to a greater extent than our own reading. TIM BERNERS-LEE, 1994
15. THE INTERNET, 1994 C.A. NEW! NEW! No Google, Wikipedia, Amazon, … yet!
16. I have a dream for the Web [in which computers] become capable of analyzing all the data on the Web – the content, links, and transaction 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. TIM BERNERS-LEE, 1999 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
17. THE SEMANTIC WEB IS A WEB OF DATA THE SEMANTIC WEB IS THE WEB same base technologies, evolutionary, decentralized IT IS ABOUT COMMON FORMATS for integration and combination of data drawn from diverse sources IT IS ABOUT A LANGUAGE for recording how the data relates to real world objects
18. WHAT IS THE RELATIONSHIP WITH AI? INFLUENCE Some technologies in the Semantic Web benefited a lot from AI research and development (and viceversa) DIFFERENT GOALS Artificial Intelligence approach: build smarter machines, teach computers to infer the meaning of data Semantic Web approach: have smarter data, make data easier for machines to find, access and process
19. FUNDAMENTALS
20. RESOURCE AND DESCRIPTION RESOURCE every document “reachable” on the Web no matter the content, format, language, etc. RESOURCE DESCRIPTION independent from the format standard language (based on metadata)
21. RESOURCE AND DESCRIPTION Resources
22. RESOURCE AND DESCRIPTION Description
23. RESOURCE AND DESCRIPTION Description Title Author Date Topic Quality Title Author Date Topic
24. URIS unambiguous names for resources RDF a common data model to connect and describe resources SPARQL access to the data model RDFS, OWL common description languages OWL, RIF reasoning (mainly logic inference)
25. MODELING DATA
26. EXAMPLE: BOOKSTORE Represent the following data about the AI book as a set of relations Title: “Artificial Intelligence: A Modern Approach” Author: Russel, Stuart and Norvig, Peter Publisher: Prentice Hall ISBN: 978-0136042594
27. EXAMPLE: BOOKSTORE http://...isbn/9780136042594 Resource
28. EXAMPLE: BOOKSTORE http://...isbn/9780136042594 Artificial Intelligence: A Modern Approach Literal
29. EXAMPLE: BOOKSTORE http://...isbn/9780136042594 Artificial Intelligence: A Modern Approach title
30. EXAMPLE: BOOKSTORE http://...isbn/9780136042594 Artificial Intelligence: A Modern Approach Prentice Hall Russel, Stuart Norvig, Peter title publisher author author
31. RDF: RESOURCE DESCRIPTION FRAMEWORK STRUCTURED IN STATEMENTS SUBJECT a resource (URI) PREDICATE a verb, property or relationship OBJECT a resource or a literal string
32. EXAMPLE: BOOKSTORE http://...isbn/9780136042594 Artificial Intelligence: A Modern Approach Prentice Hall Russel, Stuart Norvig, Peter title publisher author author Subject Object Object Object Object Predicate Predicate Predicate
33. EXAMPLE: BOOKSTORE http://...isbn/9780136042594 Artificial Intelligence: A Modern Approach title RDF IN XML SYNTAX <rdf:RDF xmlns:rdf=http://www.w3.org/…/22-rdf-syntax-ns#> <rdf:Description about=“http://... isbn/9780136042594”> <title>Artificial Intelligence: A Modern Approach</title> </rdf:Description> </RDF>
34. EXAMPLE: BOOKSTORE http://...isbn/9780136042594 Artificial Intelligence: A Modern Approach title RDF IN TURTLE <http://... isbn/9780136042594> title “Artificial Intelligence: A Modern Approach”
35. LINKIN’ DATA
36. EXAMPLE: BOOKSTORE Represent the following data about the Italian translation of the AI book as a set of relations Title: “Intelligenza artificiale. Un approccio moderno” Author: Russel, Stuart and Norvig, Peter Publisher: Prentice Hall ISBN: 978-8871925936 Original ISBN: 978-0136042594
37. EXAMPLE: BOOKSTORE http://...isbn/9788871925936 Intelligenza Artificiale. Un approccio moderno Prentice Hall Russel, Stuart Norvig, Peter title publisher creator creator http://...isbn/9780136042594 original
38. EXAMPLE: BOOKSTORE http://...isbn/9788871925936 Intelligenza Artificiale. Un approccio moderno Prentice Hall title publisher http://...isbn/9780136042594 original http://...isbn/9780136042594 Artificial Intelligence: A Modern Approach Prentice Hall title publisher
39. EXAMPLE: BOOKSTORE http://...isbn/9788871925936 Intelligenza Artificiale. Un approccio moderno Prentice Hall title publisher http://...isbn/9780136042594 original http://...isbn/9780136042594 Artificial Intelligence: A Modern Approach Prentice Hall title creator same URI, same resource
40. EXAMPLE: BOOKSTORE http://...isbn/9780136042594 Artificial Intelligence: A Modern Approach Prentice Hall Russel, Stuart Norvig, Peter title publisher author author http://...isbn/9788871925936 Intelligenza Artificiale. Un approccio moderno Prentice Hall title publisher original Russel, Stuart Norvig, Peter creator creator
41. EXAMPLE: BOOKSTORE http://...isbn/9780136042594 Artificial Intelligence: A Modern Approach Prentice Hall Russel, Stuart Norvig, Peter title publisher author author http://...isbn/9788871925936 Intelligenza Artificiale. Un approccio moderno Prentice Hall title publisher original Russel, Stuart Norvig, Peter creator creator What about merging creator and author? In RDF, it is not possible!
42. PROBLEM: FIELD NAMES ARE ARBITRARY Synonyms : author or creator or maker or contributor or… Singular or plural: author or authors SOLUTION: STANDARDS general or domain-specific
43. DUBLIN CORE GENERAL VOCABULARY Dublin Core Metadata Initiative (DCMI) http://dublincore.org BUILDING BLOCKS TO DEFINE METADATA FOR THE SEMANTIC WEB Define title, contributor, publisher, license, date, language, etc.
44. PROBLEM: FIELD VALUES ARE ARBITRARY Value type: string, date, integer, … Value format: “Norvig, Peter” or “Norvig, P.” or “Peter Norvig” or… Value restrictions: one value or multiple values (how many?) SOLUTIONS Standards Controlled vocabulary (close list of terms) Semantically rich descriptions to support search (RDFS and/or OWL)
45. FRIEND OF A FRIEND (FOAF) GENERAL ONTOLOGY Describe persons, their activities and their relations to other people and objects http://www.foaf-project.org BUILDING BLOCKS TO DEFINE STRUCTURED RELATIONS BETWEEN PEOPLE Define name, familyName, givenName, knows, age, nick, etc.
46. EXAMPLE: BOOKSTORE http://...isbn/9780136042594 Artificial Intelligence: A Modern Approach Prentice Hall Russel, Stuart Norvig, Peter dc:title dc:publisher dc:creator dc:creator foaf: http://xmlns.com/foaf/spec dc: http://purl.org/dc/terms foaf:name foaf:name foaf:name
47. http://...isbn/9780136042594 Norvig, Peter dc:creator foaf:name http://...isbn/9780136042594 Norvig, Peter author WHY?
48. RDF SCHEMA
49. RDF SCHEMA SCHEMA Definition of the nodes and predicates used in a RDF document DOMAIN AND RANGE RDFS describes properties in terms of classes of resource to which they apply (from a “domain” to a “range”)
50. EXAMPLE RDF data http://elite.polito.it/people/derussis teaches http://bit.ly/lingambmult
51. http://elite.polito.it/people/derussis teaches EXAMPLE RDF data RDF schema http://bit.ly/lingambmult Teacher Person teaches Course domain range subClassOf type type
52. http://...isbn/9780136042594 Norvig, Peter dc:creator foaf:name http://...isbn/9780136042594 Norvig, Peter author BACK TO THE BOOKSTORE EXAMPLE…
53. http://...isbn/9780136042594 Norvig, Peter dc:creator foaf:name http://...isbn/9780136042594 Norvig, Peter author BACK TO THE BOOKSTORE EXAMPLE… dc:creator has range Agent, i.e., a class (resource), not a literal: we use an anonymous class for this scope. Finally, foaf:Name has range rdfs:Literal. anonymous class
54. RDFS EXPRESSIVITY SIMPLE RELATIONSHIP BETWEEN THINGS RDFS provides a vocabulary to express relationship between things (e.g., subClassOf or type) AVOID COMPLEX RELATIONSHIP RDFS cannot describe data in terms of set of operations (e.g., unionOf), equivalence (e.g., sameAs) or cardinality (e.g., allValueFrom)
55. OWL
56. WEB ONTOLOGY LANGUAGE WHAT? OWL (version 2): a knowledge representation language Designed to formulate, exchange and reason with knowledge about a domain of interest
57. WEB ONTOLOGY LANGUAGE INDIVIDUALS, CLASSES AND PROPERTIES “Politecnico di Torino is a university” “Politecnico di Torino has a professor named Elio Piccolo” “Politecnico di Torino” is an object: an individual in OWL2 “university” is a category: a class in OWL2 “has a professor” is a relation: a property in OWL2 “Elio Piccolo” is an individual, too
58. WEB ONTOLOGY LANGUAGE EXPRESSIVITY Designed to represent rich and complex knowledge about things, group of things, and their relations LOGIC-BASED Knowledge expressed in OWL can be reasoned with a computer program to verify its consistency or to make implicit knowledge explicit
59. WEB ONTOLOGY LANGUAGE LINKED Ontologies in OWL can be published on the Web and may refer to or be referred from other OWL ontologies CHOOSE THE SYNTAX YOU LIKE Various syntaxes available for OWL, for different purposes (RDF/XML, Turtle, Manchester, etc.)
60. EXAMPLE: BOOKSTORE Intelligenza Artificiale. Un approccio moderno Prentice Hall dc:title dc:publisher Artificial Intelligence: A Modern Approach Prentice Hall dc:title dc:publisher Libro Book rdfs:type rdf:type http://...isbn/9788871925936 http://...isbn/9780136042594
61. EXAMPLE: BOOKSTORE Intelligenza Artificiale. Un approccio moderno Prentice Hall dc:title dc:publisher Artificial Intelligence: A Modern Approach Prentice Hall dc:title dc:publisher Libro Book rdfs:type rdf:type owl:sameAs http://...isbn/9788871925936 http://...isbn/9780136042594
62. HANDS ON OWL
63. EXAMPLE: BOOKSTORE It is time to sell the books we modeled. Users must have the possibility to search in our book catalog. We need to describe our store and add some other information about the books. GoodRelations helps in realizing such an example: http://www.heppnetz.de/projects/goodrelations/
64. EXAMPLE: BOOKSTORE BUILD THE MODEL 1. Describe the business entity 2. Describe the offered items 3. Describe the offer 4. Link the offer to the business entity SEARCH IN THE MODEL
65. DESCRIBE THE BUSINESS ENTITY default:BookStore_1 a gr:BusinessEntity ; gr:legalName “bookstore.com Ltd.”^^xsd:string . Bookstore_1
66. DESCRIBE THE OFFERED ITEMS default:AIBook_en a item:Book, gr:ActualProductOrServiceInstance ; item:hasTotalPages default:QuantitativeValueInteger_1 . AIBook_en default:QuantitativeValueInteger_1 a gr:QuantitativeValueInteger ; gr:hasValue “1132”^^xsd:integer . QuantitativeValue Integer_1
67. Bookstore_1 AIBook_en item:Book QuantitativeValue Integer_1 1132 gr:ActualProductOrServiceInstance gr:ProductOrService rdf:type rdfs:subClassOf rdf:type item:hasTotalPages gr:hasValue
68. DESCRIBE THE OFFER default:Offering_1 a gr:Offering ; gr:hasBusinessFunction gr:Sell ; gr:hasPriceSpecification default:UnityPriceSpecification_1 ; gr:includeObject default:TypeAndQuantityNode_1 . Offering_1
69. Bookstore_1 Offering_1 TypeAndQuantity Node_1 UnitPriceSpecification_1 AIBook_en item:Book QuantitativeValue Integer_1 gr:Sell 1.0 1132 gr:ActualProductOrServiceInstance gr:ProductOrService gr:includeObject gr:hasBusinessFunction gr:hasPriceSpecification gr:amountOfThisGood rdf:type rdfs:subClassOf rdf:type item:hasTotalPages gr:hasValue gr:Offering rdf:type
70. DESCRIBE THE OFFER default:TypeAndQuantityNode_1 a gr:TypeAndQuantityNode ; gr:amountOfThisGood “1.0”^^xsd:float ; gr:typeOfGood default:AIBook_en . default:UnitPriceSpecification_1 a gr:UnitPriceSpecification ; gr:hasCurrency “EUR”^^xsd:string ; gr:hasCurrencyValue “120.0”^^xsd:float . TypeAndQuantity Node_1 UnitPriceSpecification_1
71. Bookstore_1 Offering_1 TypeAndQuantity Node_1 UnitPriceSpecification_1 AIBook_en item:Book QuantitativeValue Integer_1 gr:Sell 120.0 “EUR” 1.0 1132 gr:ActualProductOrServiceInstance gr:ProductOrService gr:includeObject gr:hasBusinessFunction gr:hasPriceSpecification gr:hasCurrency gr:hasCurrencyValue gr:amountOfThisGood gr:typeOfGood rdf:type rdfs:subClassOf rdf:type item:hasTotalPages gr:hasValue gr:Offering rdf:type
72. default:BookStore_1 gr:offers default:Offering_1 LINK THE OFFER TO THE BUSINESS ENTITY
73. Bookstore_1 Offering_1 TypeAndQuantity Node_1 UnitPriceSpecification_1 AIBook_en item:Book QuantitativeValue Integer_1 gr:Sell 120.0 “EUR” 1.0 1132 gr:ActualProductOrServiceInstance gr:ProductOrService gr:offers gr:includeObject gr:hasBusinessFunction gr:hasPriceSpecification gr:hasCurrency gr:hasCurrencyValue gr:amountOfThisGood gr:typeOfGood rdf:type rdfs:subClassOf rdf:type item:hasTotalPages gr:hasValue gr:Offering rdf:type
74. QUERY THE WHOLE! PREFIX gr: <http://purl.org/goodrelations/v1#> PREFIX item: <http://www.elite.polito.it/ontologies/example/item#> SELECT ?offering WHERE { ?offering rdf:type gr:Offering . ?offering gr:includesObject ?object . ?object gr:typeOfGood ?item . ?item rdf:type item:Book . } How to get all the available offer for the book? SPARQL
75. QUERY THE WHOLE! ?item rdf:type item:Book . SPARQL ?item item:Book rdf:type
76. QUERY THE WHOLE! ?object gr:typeOfGood ?item . SPARQL ?object AIBook_en item:Book gr:typeOfGood rdf:type
77. QUERY THE WHOLE! ?offering gr:includesObject ?object . SPARQL ?offering TypeAndQuantity Node_1 AIBook_en item:Book gr:includeObject gr:typeOfGood rdf:type
78. QUERY THE WHOLE! ?offering rdf:type gr:Offering . SPARQL ?offering TypeAndQuantity Node_1 AIBook_en item:Book gr:includeObject gr:typeOfGood rdf:type gr:Offering rdf:type
79. QUERY THE WHOLE! SELECT ?offering SPARQL Offering_1 TypeAndQuantity Node_1 AIBook_en item:Book gr:includeObject gr:typeOfGood rdf:type gr:Offering rdf:type
80. REFERENCES Semantic Web standards: http://w3c.org/standards/semanticweb Semantic Web Wiki: http://semanticweb.org Semantic Web FAQ: http://www.w3c.org/2001/sw/SW-FAQ Book: A Semantic Web Primer (http://www.semanticwebprimer.org) Book: Semantic Web Programming (http://semwebprogramming.org) Last access: 26 May 2014
81. THANKS! Luigi De Russis http://elite.polito.it
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