14.3 Ontologies and Knowledge Sharing

14.3.1 Uniform Resource Identifiers

A Uniform Resource Identifier (URI) is a unique identifier for individuals or properties, or what is called resources. In the semantic web languages URIs are typically of the form url#name, where url is of the form of a web page. This is often abbreviated to abbr:name, where abbr is an abbreviation that is locally declared to be an abbreviation for the full URI.

A URI has meaning because people use it with that meaning.

Example 14.12.

The friend-of-a-friend (foaf) project is a simple ontology for publishing personal information about people.

The URI http://xmlns.com/foaf/0.1/#name is a property that relates a person and a string representation of the person’s name. If someone intends to use this particular property, using this URI will enable others who also adopt this ontology (or map to it) to know which property is meant. As long as everyone who use the URI ¡http://xmlns.com/foaf/0.1/#name¿ means the same property, it does not matter what is at the URL http://xmlns.com/foaf/0.1/. That URL, at the time of writing, just redirects to a web page. However, the “friend-of-a-friend” project uses that name space to mean something. This works simply because people use it that way.