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Network Working Group                                           N. Walsh
Internet-Draft                                          Sun Microsystems
Intended status: Best Current                                   R. Tobin
Practice                                         University of Edinburgh
Expires: November 15, 2007                                  May 14, 2007


                  Human Readable Resource Identifiers
                       draft-walsh-tobin-hrri-01

Status of this Memo

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Copyright Notice

   Copyright (C) The IETF Trust (2007).













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Abstract

   This memo defines Human Readable Resource Identifiers, strings which
   are interpreted as IRIs, but which allow the use of characters which
   must be escaped in a legal IRI, such as delimiters and a few other
   ASCII characters.


Table of Contents

   1.    Introduction . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.    Motivation . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.    Human Readable Resource Identifiers  . . . . . . . . . . . .  5
   4.    Relation to IRIs . . . . . . . . . . . . . . . . . . . . . .  6
   5.    Security Considerations  . . . . . . . . . . . . . . . . . .  7
   6.    IANA Considerations  . . . . . . . . . . . . . . . . . . . .  8
   7.    References . . . . . . . . . . . . . . . . . . . . . . . . .  9
   7.1.  Normative References . . . . . . . . . . . . . . . . . . . .  9
   7.2.  Informative References . . . . . . . . . . . . . . . . . . .  9
         Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 10
         Intellectual Property and Copyright Statements . . . . . . . 11






























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1.  Introduction

   The syntactic constraints of IRIs (RFC 3987[3]) and URIs (RFC
   3986[1]) mandate that certain common punctuation characters (such as
   spaces, quotation marks, and various sorts of delimiters) must be
   percent encoded.  However, it is often inconvenient for authors to
   encode these characters.

   Historically, XML system identifiers and, more generally, the value
   of XML attributes that are intended to contain IRIs or URIs have
   allowed authors to provide values that use these characters
   literally.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119[2].



































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2.  Motivation

   Several XML-related specifications use strings which are interpreted
   as IRIs, but which allow the use of characters which must be escaped
   in a legal IRI, such as delimiters and a few other ASCII characters.
   Examples include XML System Identifiers[4], the href attribute in
   XLink[5], and XML Base attributes[6].  These specifications all
   describe, with slightly different wording, the same algorithm for
   converting that string to a URI or IRI.  The purpose of this RFC is
   to provide a single definition which can be referenced by these
   specifications, and to provide a name for strings of this type: Human
   Readable Resource Identifiers.







































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3.  Human Readable Resource Identifiers

   A Human Readable Resource Identifier (HRRI) is a sequence of Unicode
   characters that can be converted into an IRI by the application of a
   few simple encoding rules.

   To convert a Human Readable Resource Identifier to an IRI reference,
   the following characters MUST be percent encoded:

   o  the control characters #x0 to #x1F and #x7F to #x9F

   o  space #x20

   o  the delimiters "<" #x3C, ">" #x3E, and """ #x22

   o  the unwise characters "{" #x7B, "}" #x7D, "|" #x7C, "\" #x5C,
      "^" #x5E, and "`" #x60

   These characters are percent encoded by applying steps 2.1 to 2.3 of
   Section 3.1 of RFC 3987[3] to them.

   Some strings are not Human Readable Resource Identifiers; for
   example, the string "%%%" is not an HRRI.  A string is a legal Human
   Readable Resource Identifier if and only if the string generated by
   applying the encoding rules above is a legal IRI.

   Note that in XML, the control character #x0 can never appear.  Also,
   authors of HRRIs are advised to percent encode space characters
   themselves, rather than rely on the processor to do so, because
   spaces are often used to separate HRRIs in a sequence.

   Processing a relative identifier against a base is handled
   straightforwardly; the algorithms of RFC 3986[1] can be applied
   directly, treating the characters additionally allowed in HRRIs in
   the same way that unreserved characters are treated in URI
   references.

   If required, the IRI reference resulting from percent encoding an
   HRRI can be converted to a URI reference by following the
   prescriptions of Section 3.1 of RFC 3987[3].

   Conversion from a Human Readable Resource Identifier to an IRI or a
   URI MUST be performed only when absolutely necessary and as late as
   possible in a processing chain.  In particular, neither the process
   of converting a relative Human Readable Resource identifier to an
   absolute one nor the process of passing a Human Readable Resource
   Identifier to a process or software component responsible for
   dereferencing it SHOULD trigger percent encoding.



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4.  Relation to IRIs

   Internationalized Resource Identifiers (IRIs)[3] extend URIs by
   allowing unescaped non-ascii characters.  Human Readable Resource
   Identifiers go further by allowing various ASCII characters that are
   illegal in both URIs and IRIs.  By escaping these characters Human
   Readable Resource Identifiers can be converted to IRIs, which can in
   turn be converted to URIs if required.











































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5.  Security Considerations

   A Human Readable Resource Identifier does not in itself pose a
   security threat.  However, Human Readable Resource Identifers are
   often converted to IRIs or URIs and subsequently used to provide a
   compact set of instructions for access to network resources, care
   must be taken to properly interpret the data within a Human Readable
   Resource Identifier, to prevent that data from causing unintended
   access, and to avoid including data that should not be revealed in
   plain text.









































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6.  IANA Considerations

   This document has no actions for IANA.
















































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7.  References

7.1.  Normative References

   [1]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
        Resource Identifier (URI): Generic Syntax", RFC 3986,
        January 2005.

   [2]  Bradner, S., "Key words for us in RFCs to Indicate Requirement
        Levels", March 1997.

   [3]  Duerst, M. and M. Suignard, "Internationalized Resource
        Identifiers (IRIs)", RFC 3987, January 2005.

7.2.  Informative References

   [4]  Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E., and F.
        Yergeau, "Extensible Markup Language (XML) 1.0 (Forth Edition)",
        September 2006.

   [5]  DeRose, S., Maler, E., and D. Orchard, "XML Linking Language
        (XLink) Version 1.0", June 2001.

   [6]  Marsh, J., "XML Base", June 2001.



























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Authors' Addresses

   Norman Walsh
   Sun Microsystems
   1 Network Drive
   Building #2 MS UBUR02-201
   Burlington, MA  01803
   US

   Email: Norman.Walsh@Sun.COM


   Richard Tobin
   University of Edinburgh
   HCRC, School of Informatics
   2 Buccleuch Place
   Edinburgh  EH8 9LW
   UK

   Email: richard@inf.ed.ac.uk































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