Uniform Resource Identifiers (URI): Generic Syntax
RFC 2396

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Network Working Group                                     T. Berners-Lee
Request for Comments: 2396                                       MIT/LCS
Updates: 1808, 1738                                          R. Fielding
Category: Standards Track                                    U.C. Irvine
                                                             L. Masinter
                                                       Xerox Corporation
                                                             August 1998

           Uniform Resource Identifiers (URI): Generic Syntax

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.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

IESG Note

   This paper describes a "superset" of operations that can be applied
   to URI.  It consists of both a grammar and a description of basic
   functionality for URI.  To understand what is a valid URI, both the
   grammar and the associated description have to be studied.  Some of
   the functionality described is not applicable to all URI schemes, and
   some operations are only possible when certain media types are
   retrieved using the URI, regardless of the scheme used.

Abstract

   A Uniform Resource Identifier (URI) is a compact string of characters
   for identifying an abstract or physical resource.  This document
   defines the generic syntax of URI, including both absolute and
   relative forms, and guidelines for their use; it revises and replaces
   the generic definitions in RFC 1738 and RFC 1808.

   This document defines a grammar that is a superset of all valid URI,
   such that an implementation can parse the common components of a URI
   reference without knowing the scheme-specific requirements of every
   possible identifier type.  This document does not define a generative
   grammar for URI; that task will be performed by the individual
   specifications of each URI scheme.

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RFC 2396                   URI Generic Syntax                August 1998

1. Introduction

   Uniform Resource Identifiers (URI) provide a simple and extensible
   means for identifying a resource.  This specification of URI syntax
   and semantics is derived from concepts introduced by the World Wide
   Web global information initiative, whose use of such objects dates
   from 1990 and is described in "Universal Resource Identifiers in WWW"
   [RFC1630].  The specification of URI is designed to meet the
   recommendations laid out in "Functional Recommendations for Internet
   Resource Locators" [RFC1736] and "Functional Requirements for Uniform
   Resource Names" [RFC1737].

   This document updates and merges "Uniform Resource Locators"
   [RFC1738] and "Relative Uniform Resource Locators" [RFC1808] in order
   to define a single, generic syntax for all URI.  It excludes those
   portions of RFC 1738 that defined the specific syntax of individual
   URL schemes; those portions will be updated as separate documents, as
   will the process for registration of new URI schemes.  This document
   does not discuss the issues and recommendation for dealing with
   characters outside of the US-ASCII character set [ASCII]; those
   recommendations are discussed in a separate document.

   All significant changes from the prior RFCs are noted in Appendix G.

1.1 Overview of URI

   URI are characterized by the following definitions:

      Uniform
         Uniformity provides several benefits: it allows different types
         of resource identifiers to be used in the same context, even
         when the mechanisms used to access those resources may differ;
         it allows uniform semantic interpretation of common syntactic
         conventions across different types of resource identifiers; it
         allows introduction of new types of resource identifiers
         without interfering with the way that existing identifiers are
         used; and, it allows the identifiers to be reused in many
         different contexts, thus permitting new applications or
         protocols to leverage a pre-existing, large, and widely-used
         set of resource identifiers.

      Resource
         A resource can be anything that has identity.  Familiar
         examples include an electronic document, an image, a service
         (e.g., "today's weather report for Los Angeles"), and a
         collection of other resources.  Not all resources are network
         "retrievable"; e.g., human beings, corporations, and bound
         books in a library can also be considered resources.

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