Linked Data & Semantic Web Technology The Semantic Web Part 3. URI for the Semantic Web Dr. Myungjin Lee

Linked Data & Semantic Web Technology 2

How to Identify Objects? 3 Concept Object Symbol “Namdeamun” symbolize stand for refer to Concept Object Symbol URI symbolize stand for refer to

Linked Data & Semantic Web Technology URI, Thing, and Representation 4 Thing URI Representation Namdaemun | kdata.kr Namdaemun at kdata.kr identifies and names represents looks up URI URI links refers Person Machine

Linked Data & Semantic Web Technology 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 5

Linked Data & Semantic Web Technology How to call Jim? URN – resource identification by name – teacher: “Student Jim!” URL – resource identification as location – teacher: “Student who seats in the 2 nd row and 3 rd column JohnGraceJin 2SamTomJim 3KevinDanScott in a class

Linked Data & Semantic Web Technology Syntax of URN and URL URN – urn: : – Examples urn:isbn: urn:issn: urn:ietf:rfc:2648 URL – – Examples

Linked Data & Semantic Web Technology 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

Linked Data & Semantic Web Technology 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. 9

Linked Data & Semantic Web Technology URIs for Real-World Objects 10 Thing URI Representation for Web Browsers Namdaemun | kdata.kr Namdaemun at kdata.kr identifies and names represents looks up Person Machine Description for Agents describes

Linked Data & Semantic Web Technology The Desired Relationships 11 a foaf:Person; foaf:name "Alice"; foaf:mbox ; foaf:homepage. ID RDFHTML Resource identifier (URI) RDF document URIHTML document URI for web browsersfor semantic web applications

Linked Data & Semantic Web Technology 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 12

Linked Data & Semantic Web Technology Hash URIs URIs to represent the company, Alice, and Bob – Example Inc., the company – Bob, the person – Alice, the person 13

Linked Data & Semantic Web Technology 303 URIs forwarding to Document(s) URIs to represent the company, Alice and Bob – Example Inc., the company – Bob, the person – Alice, the person 14

Linked Data & Semantic Web Technology 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 15

Linked Data & Semantic Web Technology Cool URIs Simplicity – short and mnemonic Stability – remain as long as possible Manageability – issue your URIs in a way that you can manage 16

Linked Data & Semantic Web Technology 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 – Identifier for Alice, the person – Alice's homepage – RDF document with description of Alice 17 foaf:page ; rdfs:isDefinedBy ; a foaf:Person; foaf:name "Alice"; foaf:mbox ;...

Linked Data & Semantic Web Technology 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 18 URI TypeURI structureExamples Identifier Document Representation {doc.file-extension} Definition of the scheme concept List of scheme identifiers Set

Linked Data & Semantic Web Technology 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: Example – States and Territories Owner – federal Suggested – Example – 19 ' BASE '/' 'id' '/' ORG '/' CATEGORY ( '/' TOKEN )+

Linked Data & Semantic Web Technology 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 20 Encoding (server side/ undefined) us-asciior %HHutf-8 or %HH original characters bytesURIIRI Marchus-ascii/utf-84D March Märziso D E4 72 7AM%E4rz Märzmacintosh4D 8A 72 7AM%8Arz Märzutf-84D C3 A4 72 7AM%C3%A4rzMärz

Linked Data & Semantic Web Technology References