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What is a URI - EU Vocabularies
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Semantic knowledge base

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What is a URI

A Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource (IETF RFC3986).

URIs are specified as being written only in ASCII characters, i.e. the Roman alphabet with no accents plus a few punctuation symbols. For reasons given later (section 4.10), the advice is that only ASCII characters, i.e. only URIs, should be used as persistent identifiers.

URIs can identify anything, including:

  • Web documents: The most familiar related term is probably URL, Uniform Resource Location, which identifies a specific information resource on the World Wide Web, such as a Web page, a PDF document, an image etc. URLs all begin with http://.
  • Real-world things: The more general term, Uniform Resource Identifier (URI), can identify anything whether it's something on the Web or not.  As formulated in the W3C Note[1]: “URIs identify not just Web documents, but also real-world objects like people and cars, and even abstract ideas and non-existing things like a mythical unicorn. We call these real-world objects or things.”

While a URI has a form of presentation that could be confused with a URL, not every URI is also a URL.


[1] Cool URIs for the Semantic Web, http://www.w3.org/TR/cooluris

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