Network Working Group                                     T. Berners-Lee
Request for Comments: 1630                                          CERN
Category: Informational                                        June 1994


                 Universal Resource Identifiers in WWW(‘±‚«)

                A Unifying Syntax for the Expression of
             Names and Addresses of Objects on the Network
                     as used in the World-Wide Web


The Need For a Universal Syntax

   This section describes the concept of the URI and does not form part
   of the specification.

   Many protocols and systems for document search and retrieval are
   currently in use, and many more protocols or refinements of existing
   protocols are to be expected in a field whose expansion is explosive.

   These systems are aiming to achieve global search and readership of
   documents across differing computing platforms, and despite a
   plethora of protocols and data formats.  As protocols evolve,
   gateways can allow global access to remain possible. As data formats
   evolve, format conversion programs can preserve global access.  There
   is one area, however, in which it is impractical to make conversions,
   and that is in the names and addresses used to identify objects.
   This is because names and addresses of objects are passed on in so
   many ways, from the backs of envelopes to hypertext objects, and may
   have a long life.

   A common feature of almost all the data models of past and proposed
   systems is something which can be mapped onto a concept of "object"
   and some kind of name, address, or identifier for that object.  One
   can therefore define a set of name spaces in which these objects can
   be said to exist.

   Practical systems need to access and mix objects which are part of
   different existing and proposed systems.  Therefore, the concept of
   the universal set of all objects, and hence the universal set of
   names and addresses, in all name spaces, becomes important.  This
   allows names in different spaces to be treated in a common way, even
   though names in different spaces have differing characteristics, as
   do the objects to which they refer.

   URIs

      This document defines a way to encapsulate a name in any
      registered name space, and label it with the the name space,
      producing a member of the universal set.  Such an encoded and
      labelled member of this set is known as a Universal Resource
      Identifier, or URI.

      The universal syntax allows access of objects available using
      existing protocols, and may be extended with technology.

      The specification of the URI syntax does not imply anything about
      the properties of names and addresses in the various name spaces
      which are mapped onto the set of URI strings.  The properties
      follow from the specifications of the protocols and the associated
      usage conventions for each scheme.

   URLs

      For existing Internet access protocols, it is necessary in most
      cases to define the encoding of the access algorithm into
      something concise enough to be termed address.  URIs which refer
      to objects accessed with existing protocols are known as "Uniform
      Resource Locators" (URLs) and are listed here as used in WWW, but
      to be formally defined in a separate document.

   URNs

      There is currently a drive to define a space of more persistent
      names than any URLs.  These "Uniform Resource Names" are the
      subject of an IETF working group's discussions.  (See Sollins and
      Masinter, Functional Specifications for URNs, circulated
      informally.)

      The URI syntax and URL forms have been in widespread use by
      World-Wide Web software since 1990.