Relative Uniform Resource Locators
RFC 1808

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Network Working Group                                        R. Fielding
Request for Comments: 1808                                     UC Irvine
Category: Standards Track                                      June 1995

                   Relative Uniform Resource Locators

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   A Uniform Resource Locator (URL) is a compact representation of the
   location and access method for a resource available via the Internet.
   When embedded within a base document, a URL in its absolute form may
   contain a great deal of information which is already known from the
   context of that base document's retrieval, including the scheme,
   network location, and parts of the url-path.  In situations where the
   base URL is well-defined and known to the parser (human or machine),
   it is useful to be able to embed URL references which inherit that
   context rather than re-specifying it in every instance.  This
   document defines the syntax and semantics for such Relative Uniform
   Resource Locators.

1.  Introduction

   This document describes the syntax and semantics for "relative"
   Uniform Resource Locators (relative URLs): a compact representation
   of the location of a resource relative to an absolute base URL.  It
   is a companion to RFC 1738, "Uniform Resource Locators (URL)" [2],
   which specifies the syntax and semantics of absolute URLs.

   A common use for Uniform Resource Locators is to embed them within a
   document (referred to as the "base" document) for the purpose of
   identifying other Internet-accessible resources.  For example, in
   hypertext documents, URLs can be used as the identifiers for
   hypertext link destinations.

   Absolute URLs contain a great deal of information which may already
   be known from the context of the base document's retrieval, including
   the scheme, network location, and parts of the URL path.  In
   situations where the base URL is well-defined and known, it is useful
   to be able to embed a URL reference which inherits that context

Fielding                    Standards Track                     [Page 1]
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,