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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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Linked Data &Semantic WebTechnology
The Semantic WebPart 3. URI for the Semantic Web
Dr. Myungjin Lee
2Linked Data & Semantic Web Technology
3Linked Data & Semantic Web Technology
How to Identify Objects?
Concept
Object
Symbol
“Namdeamun”
symbolize
stand for
refer to
Concept
Object
Symbol
URI
symbolize
stand for
refer to
4Linked Data & Semantic Web Technology
URI, Thing, and Representation
Thing
URI
Representation
http://data.kdata.kr/resource/Namdaemun
<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"> at <a href="http://kdata.kr">kdata.kr</a>
identifiesand
names
represents
looks up
URIhttp://dbpedia.org/resource/Namdaemun
URIhttp://data.kdata.kr/resource/Sungnyemun
links
refers
PersonMachine
5Linked 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
6Linked 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 2nd row and 3rd column
1 2 3
1 John Grace Jin
2 Sam Tom Jim
3 Kevin Dan Scott
in a class
7Linked Data & Semantic Web Technology
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
8Linked Data & Semantic Web Technology
Cool URIs for the Semantic Web
• how to use URIs for things that are not Web pages, such as peo-ple, 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
9Linked 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 de-
scription about the resource identified by the URI from the Web.– Machines should get RDF data and humans should get a readable repre-
sentation, such as HTML.
• Be unambiguous– There should be no confusion between identifiers for Web documents and
identifiers for other resources.
10Linked Data & Semantic Web Technology
URIs for Real-World Objects
Thing
URI
Representation for Web Browsers
http://data.kdata.kr/resource/Namdaemun
<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"> at <a href="http://kdata.kr">kdata.kr</a>
identifiesand
names
represents
looks up
PersonMachine
Description for Agents<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" /> <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" />
describes
11Linked Data & Semantic Web Technology
The Desired Relationships
<URI-of-alice> a foaf:Person; foaf:name "Alice"; foaf:mbox <mailto:[email protected]>; foaf:homepage <http://www.example.com/people/alice> .
ID
RDF HTML
Resource identifier (URI)
RDF document URI HTML document URI
for web browsersfor semantic web applications
12Linked Data & Semantic Web Technology
Two Solutions for Identifying Real-World Ob-jects• 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 indica-
tion
13Linked Data & Semantic Web Technology
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
14Linked Data & Semantic Web Technology
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
15Linked Data & Semantic Web Technology
Choosing between 303 and Hash
• Hash URIs– for small and stable sets of resources when the terms are often used to-
gether– 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
16Linked 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
17Linked Data & Semantic Web Technology
Linking
• to be linked with each URI related to a real-word object to help in-formation 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 • Alice's 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:[email protected]>; ...
18Linked 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
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
Representationhttp://{domain}/doc/{concept}/{reference}/{doc.file-extension} http://education.data.gov.uk/doc/school/78/doc.rdf
Definition of the scheme concept
http://{domain}/def/{concept} http://education.data.gov.uk/def/school
List of scheme identifiers
http://{domain}/doc/{concept} http://education.data.gov.uk/doc/school
Set http://{domain}/set/{concept} http://education.data.gov.uk/set/school
19Linked 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– http://BASE/id/us/state/NAME
• Example– http://logd.tw.rpi.edu/id/us/state/Vermont
'http://' BASE '/' 'id' '/' ORG '/' CATEGORY ( '/' TOKEN )+
20Linked 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
Encoding(server side/undefined)
us-asciior %HH utf-8 or %HH
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
21Linked Data & Semantic Web Technology
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