RFC 1808 (rfc1808) - Page 2 of 16


Relative Uniform Resource Locators



Alternative Format: Original Text Document



RFC 1808           Relative Uniform Resource Locators          June 1995


   rather than re-specifying it within each instance.  Relative URLs can
   also be used within data-entry dialogs to decrease the number of
   characters necessary to describe a location.

   In addition, it is often the case that a group or "tree" of documents
   has been constructed to serve a common purpose; the vast majority of
   URLs in these documents point to locations within the tree rather
   than outside of it.  Similarly, documents located at a particular
   Internet site are much more likely to refer to other resources at
   that site than to resources at remote sites.

   Relative addressing of URLs allows document trees to be partially
   independent of their location and access scheme.  For instance, it is
   possible for a single set of hypertext documents to be simultaneously
   accessible and traversable via each of the "file", "http", and "ftp"
   schemes if the documents refer to each other using relative URLs.
   Furthermore, document trees can be moved, as a whole, without
   changing any of the embedded URLs.  Experience within the World-Wide
   Web has demonstrated that the ability to perform relative referencing
   is necessary for the long-term usability of embedded URLs.

2.  Relative URL Syntax

   The syntax for relative URLs is a shortened form of that for absolute
   URLs [2], where some prefix of the URL is missing and certain path
   components ("." and "..") have a special meaning when interpreting a
   relative path.  Because a relative URL may appear in any context that
   could hold an absolute URL, systems that support relative URLs must
   be able to recognize them as part of the URL parsing process.

   Although this document does not seek to define the overall URL
   syntax, some discussion of it is necessary in order to describe the
   parsing of relative URLs.  In particular, base documents can only
   make use of relative URLs when their base URL fits within the
   generic-RL syntax described below.  Although some URL schemes do not
   require this generic-RL syntax, it is assumed that any document which
   contains a relative reference does have a base URL that obeys the
   syntax.  In other words, relative URLs cannot be used within
   documents that have unsuitable base URLs.

2.1.  URL Syntactic Components

   The URL syntax is dependent upon the scheme.  Some schemes use
   reserved characters like "?" and ";" to indicate special components,
   while others just consider them to be part of the path.  However,
   there is enough uniformity in the use of URLs to allow a parser to
   resolve relative URLs based upon a single, generic-RL syntax.  This
   generic-RL syntax consists of six components:



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