query components are undefined, then it is a reference to the
      current document and we are done.  Otherwise, the reference URI's
      query and fragment components are defined as found (or not found)
      within the URI reference and not inherited from the base URI.

   3) If the scheme component is defined, indicating that the reference
      starts with a scheme name, then the reference is interpreted as an
      absolute URI and we are done.  Otherwise, the reference URI's
      scheme is inherited from the base URI's scheme component.

      Due to a loophole in prior specifications [RFC1630], some parsers
      allow the scheme name to be present in a relative URI if it is the
      same as the base URI scheme.  Unfortunately, this can conflict
      with the correct parsing of non-hierarchical URI.  For backwards
      compatibility, an implementation may work around such references
      by removing the scheme if it matches that of the base URI and the
      scheme is known to always use the  syntax.  The parser





 
RFC 2396                   URI Generic Syntax                August 1998


      can then continue with the steps below for the remainder of the
      reference components.  Validating parsers should mark such a
      misformed relative reference as an error.

   4) If the authority component is defined, then the reference is a
      network-path and we skip to step 7.  Otherwise, the reference
      URI's authority is inherited from the base URI's authority
      component, which will also be undefined if the URI scheme does not
      use an authority component.

   5) If the path component begins with a slash character ("/"), then
      the reference is an absolute-path and we skip to step 7.

   6) If this step is reached, then we are resolving a relative-path
      reference.  The relative path needs to be merged with the base
      URI's path.  Although there are many ways to do this, we will
      describe a simple method using a separate string buffer.

      a) All but the last segment of the base URI's path component is
         copied to the buffer.  In other words, any characters after the
         last (right-most) slash character, if any, are excluded.

      b) The reference's path component is appended to the buffer
         string.

      c) All occurrences of "./", where "." is a complete path segment,
         are removed from the buffer string.

      d) If the buffer string ends with "." as a complete path segment,
         that "." is removed.

      e) All occurrences of "/../", where  is a
         complete path segment not equal to "..", are removed from the
         buffer string.  Removal of these path segments is performed
         iteratively, removing the leftmost matching pattern on each
         iteration, until no matching pattern remains.

      f) If the buffer string ends with "/..", where 
         is a complete path segment not equal to "..", that
         "/.." is removed.

      g) If the resulting buffer string still begins with one or more
         complete path segments of "..", then the reference is
         considered to be in error.  Implementations may handle this
         error by retaining these components in the resolved path (i.e.,
         treating them as part of the final URI), by removing them from
         the resolved path (i.e., discarding relative levels above the
         root), or by avoiding traversal of the reference.




 
RFC 2396                   URI Generic Syntax                August 1998


      h) The remaining buffer string is the reference URI's new path
         component.

   7) The resulting URI components, including any inherited from the
      base URI, are recombined to give the absolute form of the URI
      reference.  Using pseudocode, this would be

         result = ""

         if scheme is defined then
             append scheme to result
             append ":" to result

         if authority is defined then
             append "//" to result
             append authority to result

         append path to result