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)" , 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 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.