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Dereferenceable Uniform Resource Identifier: Wikis


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From Wikipedia, the free encyclopedia

A dereferenceable Uniform Resource Identifier or dereferenceable URI is a resource retrieval mechanism that uses any of the internet protocols (e.g. HTTP) to obtain a copy or representation of the resource it identifies.

In the context of traditional HTML web pages, this is the normal and obvious way of working: A URI refers to the page, and when requested the web server returns a copy of it. In other non-dereferenceable contexts, such as XML Schema, the namespace identifier is still a URI, but this is simply an identifier (i.e. a namespace name). There is no intention that this can or should be dereferenced. There is even a separate attribute, schemaLocation, which may contain a dereferenceable URI that does point to a copy of the schema document.

In the case of Linked Data, the representation takes the form of a document (typically HTML or XML) that describes the resource that the URI identifies. In either case, the mechanism makes it possible for a user (or software agent) to "follow your nose" to find out more information related to the identified resource.



In the computing world, identifiers are used to distinguish things and to facilitate data exchange. For example, two American people of the same name would have different SSN. In a totally distributed system, such as the World Wide Web, a URI is used to globally identify a thing in the world. Unfortunately, because the architecture and decision made for HTTP, URIs often identifies the Web Pages instead of the underlying thing. To get rid of this confusion, URIs that identify things are often with a hash (see the following section). The following example shows the difference of a URL of a person (which usually means his/her homepage) and a URI of a person:

The benefits of using URIs to identify things is from the nature of URI: it can be dereferenced to get the information of the thing it represents, hence the term dereferenceable URI. SSN and a person's name are not dereferenceable because, even though you could google these strings, it is not guaranteed that the information exists and is unambiguous. In other words, there is no canonical way of dereferencing those identifiers. On the other hand, URIs can be dereferenced by standardized protocol such as HTTP.

Dereferenceable URIs are based on the well established theory and practices of "data access by reference". A data access and manipulation mechanism used extensively in general computer programming (e.g., C/C++ pointers) and database call level interfaces (e.g., ODBC and JDBC) amongst others. The term: dereferencing describes the act of obtaining a representation of a description of an entity via its URI.

In the Semantic Web realm, dereferencable URIs offer the critical fabric that drive the giant global graph of interconnected data popularly referred to as Linked Data; a term also coined by Tim Berners-Lee in his Linked Data Design Note[1] and furthered by other articles such as "Cool URIs for the Semantic Web" by Sauermann and Cyganiak[2].

Eventually everything will have its dereferenceable URI[3], but things that already have URIs and described in interoperable way at this moment are:


Dereferenceable URIs are constructed using one of two forms: Hash or a Slash. The critical thing about either format is the underlying use of existing Web architecture to preserve the implicit identity (or Pointer) function.


Hash URI example

Entity Berlin:

Slash URI example

Entity Berlin:


When an object has a dereferenceable URI, not only does that object have an insignia that can be used across the web, but it also provides a key to unlocking ways of providing more detail and links to relevant information about that object.

Dereferenceable URIs used in this way also enhance OpenID, when not only can the URI be an OpenID but can also provide information about that agent user. The combination of insignia, access to more information and OpenID provides an all round solution for the representation of human users on the Internet.


In summary we can establish the following facts:


  1. ^ Berners-Lee, Tim (2006), Design Note: Linked Data, W3C,, retrieved 2008-07-21  
  2. ^ Sauermann, Leo; Cyganiak, Richard (2008), Cool URIs for the Semantic Web, W3C,, retrieved 2008-07-21  
  3. ^ Berners-Lee, Tim (2006), Give yourself a URI, DIG,, retrieved 2009-01-14  

Further reading


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