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:
Fielding Standards Track