R – use of Uri and Url in semantic web

ontologyrdfsemantic-weburi

I'm working on a semantic web project and I've encountered some problems about Uri & Url.

First of all, a general question: how are Uris referenced by a user application in world wide web? Are there like Urls, stored on some international servers, and the resource is given to user application, when relevant Uri is requested? I made Uris for my ontology individuals in RDF files. Is it enough to just store an Uri in my web files? How can be sure that it is unique? (for example this is for a student: #stu00546)
Second, what Uri should i give to my ontology? should I register a valid Uri to make it work on the Internet?
Last, should I store both Uris and Url, for an individual, where it's needed? For instance if I want to create an individual about a learning resource (like a Pdf), and I want the user to be able of opening this Pdf later, should I store the Url of Pdf, or I should define this individual with it's Uri, which is assigned to it by other site?

Thank you very much for your time & attention

Best Answer

About URI: in general all URI cannot be referenced: for example

urn:isbn:0451450523

describes the id of a book, but there is not a standard way to find this book. Some protocols such as URL or LSID are associated with protocol that allow them to retrieve the information.

An URI for your ontology: This could be any unique URI (e.g. urn:me:onotology/mywebsite#ontology but I guess the best place would be a URL on the web where your ontology is described. See also the ontology header. For example the namespace of FOAF is http://xmlns.com/foaf/0.1/ which redirects to the specifiation.

A URL for your document (suggestion):

<foaf:Document rdf:about="http://example.org/mydoc1">
  <dc:title xml:lang="en">Title</dc:title>
  <dc:title xml:lang="fr">Titre</dc:title>
</foaf:Document>

<my:InstanceOfDoc rdf:about="http://example.org/mydoc1/pdf">
 <my:isInstanceOf  rdf:resource="http://example.org/mydoc1"/>
 <my:mime-type>application/pdf</my:mime-type>
</my:InstanceOfDoc>


<my:InstanceOfDoc rdf:about="http://example.org/mydoc1/txt">
 <my:isInstanceOf  rdf:resource="http://example.org/mydoc1"/>
 <my:mime-type>text/plain</my:mime-type>
</my:InstanceOfDoc>

<my:InstanceOfDoc rdf:about="http://example.org/mydoc1/html">
 <my:isInstanceOf  rdf:resource="http://example.org/mydoc1"/>
 <my:mime-type>text/html</my:mime-type>
</my:InstanceOfDoc>
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