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.









 
RFC 1630                      URIs in WWW                      June 1994


   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.
















 
RFC 1630                      URIs in WWW                      June 1994


Design Criteria and Choices

   This section is not part of the specification: it is simply an
   explanation of the way in which the specification was derived.

   Design criteria

      The syntax was designed to be:

      Extensible              New naming schemes may be added later.

      Complete                It is possible to encode any naming
                              scheme.

      Printable               It is possible to express any URI using
                              7-bit ASCII characters so that URIs may,
                              if necessary, be passed using pen and ink.

   Choices for a universal syntax

      For the syntax itself there is little choice except for the order
      and punctuation of the elements, and the acceptable characters and
      escaping rules.

      The extensibility requirement is met by allowing an arbitrary (but
      registered) string to be used as a prefix.  A prefix is chosen as