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The Semantic Web #3 - URI

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This is a lecture note #3 for my class of Graduate School of Yonsei University, Korea. …

This is a lecture note #3 for my class of Graduate School of Yonsei University, Korea.
It describes URI for the Semantic Web.

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  • 1. Linked Data &Semantic WebTechnology The Semantic Web Part 3. URI for the Semantic Web Dr. Myungjin Lee
  • 2. 2Linked Data & Semantic Web Technology
  • 3. How to Identify Objects? Object refer to Object stand for refer to Concept symbolize stand for Concept “Namdeamun” symbolize Symbol URI Symbol 3Linked Data & Semantic Web Technology
  • 4. URI, Thing, and Representation looks up URI Person http://data.kdata.kr/resource/Namdaemun Machine refers URI http://data.kdata.kr/resource/Sungnyemun links identifies and names URI Thing http://dbpedia.org/resource/Namdaemun represents Representation <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <head> <title>Namdaemun | kdata.kr</title> <link rel="alternate" type="application/rdf+xml" href="http://data.kdata.kr/data/Namdaemun" title="RDF" /> </head> <body onLoad="init();"> <div id="header"> <div> <h1 id="title">Namdaemun</h1> <div id="homelink"> &nbsp;at <a href="http://kdata.kr">kdata.kr</a> 4Linked Data & Semantic Web Technology
  • 5. URI (Uniform Resource Identifier) • a string of characters used to identify a name or a web resource • URN (Uniform Resource Name) – persistent, location-independent identifiers for resources • URL (Uniform Resource Locator) – a means of locating the resource 5Linked Data & Semantic Web Technology
  • 6. How to call Jim? in a class 1 2 3 1 John Grace Jin 2 Sam Tom Jim • URN 3 Kevin Dan Scott – resource identification by name – teacher: “Student Jim!” • URL – resource identification as location – teacher: “Student who seats in the 2nd row and 3rd column 6Linked Data & Semantic Web Technology
  • 7. Syntax of URN and URL • URN – urn:<namespace identifier>:<namespace-specific string> – Examples • urn:isbn:0451450523 • urn:issn:0167-6423 • urn:ietf:rfc:2648 • URL – scheme://username:password@domain:port/path?query_string#fragment_id – Examples • http://vnc.example.com:5800 • http://en.example.org/wiki/URL • http://semantics.kr/search?first_name=John&last_name=Doe 7Linked Data & Semantic Web Technology
  • 8. Cool URIs for the Semantic Web • how to use URIs for things that are not Web pages, such as people, products, places, ideas and concepts • how the Semantic Web can (and should) be realized as a part of the Web • W3C Interest Group Note, 03 December 2008 8Linked Data & Semantic Web Technology
  • 9. URIs for Real-World Objects • Be on the Web – Given only a URI, machines and people should be able to retrieve a description about the resource identified by the URI from the Web. – Machines should get RDF data and humans should get a readable representation, such as HTML. • Be unambiguous – There should be no confusion between identifiers for Web documents and identifiers for other resources. 9Linked Data & Semantic Web Technology
  • 10. URIs for Real-World Objects URI http://data.kdata.kr/resource/Namdaemun looks up identifies and Person names Machine Description for Agents describes <rdf:RDF> <rdf:Description rdf:about="http://dbpedia.org/resource/Namdaemun"> <rdf:type rdf:resource="http://dbpedia.org/class/yago/GatesOfKorea" /> <rdf:type rdf:resource="http://www.opengis.net/gml/_Feature" /> <owl:sameAs rdf:resource="http://pl.dbpedia.org/resource/Sungnyemun" /> <owl:sameAs rdf:resource="http://cs.dbpedia.org/resource/Namdemun" /> Thing <owl:sameAs rdf:resource="http://es.dbpedia.org/resource/Namdaemun" /> <owl:sameAs rdf:resource="http://dbpedia.org/resource/Namdaemun" /> <owl:sameAs rdf:resource="http://it.dbpedia.org/resource/Namdaemun" /> representsRepresentation for Web Browsers<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <head> <title>Namdaemun | kdata.kr</title> <link rel="alternate" type="application/rdf+xml" href="http://data.kdata.kr/data/Namdaemun" title="RDF" /></head> <body onLoad="init();"> <div id="header"> <div> <h1 id="title">Namdaemun</h1> <div id="homelink"> &nbsp;at <a href="http://kdata.kr">kdata.kr</a> 10Linked Data & Semantic Web Technology
  • 11. The Desired Relationships <URI-of-alice> a foaf:Person; foaf:name "Alice"; foaf:mbox <mailto:alice@example.com>; foaf:homepage <http://www.example.com/people/alice> . Resource identifier (URI) ID for semantic web applications for web browsers RDF HTML RDF document URI HTML document URI 11Linked Data & Semantic Web Technology
  • 12. Two Solutions for Identifying Real-World Objects • Hash URIs – using a fragment, a special part that is separated from the rest of the URI by a hash symbol (“#”) • 303 URIs forwarding to Document(s) – to use a special HTTP status code, 303 See Other, to give an indication 12Linked Data & Semantic Web Technology
  • 13. Hash URIs • URIs to represent the company, Alice, and Bob – http://www.example.com/about#exampleinc • Example Inc., the company – http://www.example.com/about#bob • Bob, the person – http://www.example.com/about#alice • Alice, the person 13Linked Data & Semantic Web Technology
  • 14. 303 URIs forwarding to Document(s) • URIs to represent the company, Alice and Bob – http://www.example.com/id/exampleinc • Example Inc., the company – http://www.example.com/id/bob • Bob, the person – http://www.example.com/id/alice • Alice, the person 14Linked Data & Semantic Web Technology
  • 15. Choosing between 303 and Hash • Hash URIs – for small and stable sets of resources when the terms are often used together – for simply uploading static RDF files to a Web server – for large sets of data that are beyond the point where it is practical to serve all related resources in a single document • 303 URIs – for such data sets, making neater-looking URIs, but with an impact on run-time performance and server load 15Linked Data & Semantic Web Technology
  • 16. Cool URIs • Simplicity – short and mnemonic • Stability – remain as long as possible • Manageability – issue your URIs in a way that you can manage 16Linked Data & Semantic Web Technology
  • 17. Linking • to be linked with each URI related to a real-word object to help information consumers understand their relation • three URIs related to Alice – http://www.example.com/id/alice • Identifier for Alice, the person – http://www.example.com/people/alice • Alices homepage – http://www.example.com/data/alice • RDF document with description of Alice <http://www.example.com/id/alice> foaf:page <http://www.example.com/people/alice>; rdfs:isDefinedBy <http://www.example.com/data/alice>; a foaf:Person; foaf:name "Alice"; foaf:mbox <mailto:alice@example.com>; ... 17Linked Data & Semantic Web Technology
  • 18. Designing URI Sets for the UK Public Sector • URIs: – name the set and describe its characteristics – identify for the real-world „Things‟ in a single concept – provide a means of looking up data on the web – provide mechanisms to: • lookup an Identifier URI and be redirected to its Document URI • discover and get each of the Representation URIs URI Type URI structure Examples Identifier http://{domain}/id/{concept}/{reference} http://education.data.gov.uk/id/school/78 Document http://{domain}/doc/{concept}/{reference} http://education.data.gov.uk/doc/school/78 http://{domain}/doc/{concept}/{reference}/ Representation http://education.data.gov.uk/doc/school/78/doc.rdf {doc.file-extension} Definition of the http://{domain}/def/{concept} http://education.data.gov.uk/def/school scheme concept List of scheme http://{domain}/doc/{concept} http://education.data.gov.uk/doc/school identifiers Set http://{domain}/set/{concept} http://education.data.gov.uk/set/school 18Linked Data & Semantic Web Technology
  • 19. URI Design Principles: Creating Unique URIs for Government Linked Data • These principles should produce: – URIs that are easily re-hosted – Concise URIs with as little "cruft" as possible – URIs that span many domains including • URI Template: http:// BASE / id / ORG / CATEGORY ( / TOKEN )+ • Example – States and Territories • Owner – federal • Suggested – http://BASE/id/us/state/NAME • Example – http://logd.tw.rpi.edu/id/us/state/Vermont 19Linked Data & Semantic Web Technology
  • 20. URI and IRI • IRI (Internationalized Resource Identifier) – While URIs are limited to a subset of the ASCII character set, IRIs may contain characters from the Universal Character Set (Unicode/ISO 10646). – use UTF-8 and %HH-escaping for conversion to URIs Encoding (server side/ us-asciior %HH utf-8 or %HH undefined) original characters <====> bytes URI IRI March us-ascii/utf-8 4D 61 72 63 68 March March März iso-8859-1 4D E4 72 7A M%E4rz M%E4rz März macintosh 4D 8A 72 7A M%8Arz M%8Arz März utf-8 4D C3 A4 72 7A M%C3%A4rz März 20Linked Data & Semantic Web Technology
  • 21. References • http://www.slideshare.net/lysander07/open-hpi-semweb02part1 • http://www.slideshare.net/onlyjiny/linkeddata • http://en.wikipedia.org/wiki/Uniform_resource_identifier • http://en.wikipedia.org/wiki/Uniform_resource_name • http://en.wikipedia.org/wiki/Uniform_resource_locator • http://www.w3.org/TR/cooluris/ • https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/60975/designing-URI-sets-uk-public-sector.pdf • http://data.gov.uk/resources/uris • http://logd.tw.rpi.edu/instance-hub-uri-design • http://en.wikipedia.org/wiki/Internationalized_Resource_Identifier • http://www.w3.org/2004/Talks/IUC25iri/Overview.html 21Linked Data & Semantic Web Technology