Network Working Group N. Walsh Internet-Draft Sun Microsystems Intended status: Best Current R. Tobin Practice University of Edinburgh Expires: October 28, 2007 April 26, 2007 Human Readable Resource Identifiers draft-walsh-tobin-hrri-00 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on October 28, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Walsh & Tobin Expires October 28, 2007 [Page 1] Internet-Draft HRRI April 2007 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 Walsh & Tobin Expires October 28, 2007 [Page 2] Internet-Draft HRRI April 2007 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]. Walsh & Tobin Expires October 28, 2007 [Page 3] Internet-Draft HRRI April 2007 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 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 an 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. Walsh & Tobin Expires October 28, 2007 [Page 4] Internet-Draft HRRI April 2007 3. Human Readable Resource Identifiers A Human Readable Resource Identifier 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 (HRRIs); 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 XML resource identifiers in the same way that unreserved characters are in URI references. If required, the IRI reference resulting from percent encoding an XML Resource Identifier 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. Walsh & Tobin Expires October 28, 2007 [Page 5] Internet-Draft HRRI April 2007 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. Walsh & Tobin Expires October 28, 2007 [Page 6] Internet-Draft HRRI April 2007 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. Walsh & Tobin Expires October 28, 2007 [Page 7] Internet-Draft HRRI April 2007 6. IANA Considerations This document has no actions for IANA. Walsh & Tobin Expires October 28, 2007 [Page 8] Internet-Draft HRRI April 2007 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. Walsh & Tobin Expires October 28, 2007 [Page 9] Internet-Draft HRRI April 2007 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 Walsh & Tobin Expires October 28, 2007 [Page 10] Internet-Draft HRRI April 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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