Network Working Group J. Snell Internet-Draft January 4, 2008 Updates: 4287 (if approved) Intended status: Standards Track Expires: July 7, 2008 Atom Syndication Format Tombstones draft-snell-atompub-tombstones-04.txt 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 July 7, 2008. Copyright Notice Copyright (C) The IETF Trust (2008). Abstract This specification adds mechanisms to the Atom Syndication Format which Atom Feed publishers can use to explicitly indicate that specific Atom entries have been removed from an Atom feed. Snell Expires July 7, 2008 [Page 1] Internet-Draft Atom Tombstones January 2008 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3 3. The at:deleted-entry element . . . . . . . . . . . . . . . . . 3 4. The Trash Link Relation . . . . . . . . . . . . . . . . . . . . 4 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 6.1. The Link Relation Registration "Trash" . . . . . . . . . . 6 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 8. Normative References . . . . . . . . . . . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6 Intellectual Property and Copyright Statements . . . . . . . . . . 8 Snell Expires July 7, 2008 [Page 2] Internet-Draft Atom Tombstones January 2008 1. Introduction This specification adds a new element to the Atom Syndication Format [RFC4287] that can be used to explicitly indicate that specific Atom entries have been removed from an Atom Feed Document. 2. Notational Conventions 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 BCP 14, [RFC2119] This specification uses XML Namespaces [W3C.REC-xml-names-19990114] to uniquely identify XML element names. It uses the following namespace prefix for the indicated namespace URI; "at": "http://purl.org/atompub/tombstones/1.0" 3. The at:deleted-entry element The at:deleted-entry element MAY appear as a child of atom:feed to represent an Atom Entry that has been removed from the feed. deletedEntry = element at:deleted-entry { atomCommonAttributes, attribute ref { atomUri }, attribute when { atomDateConstruct }?, ( element at:by { atomPersonConstruct}?, & element at:comment {atomTextConstruct}?, & extensionElement* ) } The at:deleted-entry element MUST contain a ref attribute whose value specifies the atom:id of the entry that has been removed. The at:deleted-entry element MAY contain a when element whose value is an [RFC3339] "date-time" specifying the instant the entry was deleted. An uppercase "T" character MUST be used to separate date and time, and an uppercase "Z" character MUST be present in the absence of a numeric time zone offset The at:deleted-entry element MAY contain one at:by element used to identify the entity that removed the entry from the feed. The at:by element is an Atom Person Construct as defined by Section 3.2 of [RFC4287]. Snell Expires July 7, 2008 [Page 3] Internet-Draft Atom Tombstones January 2008 The at:deleted-entry element MAY contain one at:comment element whose value provides additional information about the deletion operation. The atom:comment element is an Atom Text Construct as defined by Section 3.1 of [RFC4287]. Atom Feed Documents MAY contain any number of at:deleted-entry elements, but MUST NOT contain more than one with the same ref attribute value. ... John Doe jdoe@example.org Removed comment spam ... An Atom feed MAY contain atom:entry elements and at:deleted-entry elements sharing the same atom:id value. Atom processors MUST ignore any at:deleted-entry elements sharing an atom:id value with an atom: entry whose atom:updated element specifies a date and time more recent than the at:deleted-entry element's when value. If the at: deleted-entry element does not contain a when element, the at: deleted-entry sharing the same atom:id as an entry MUST be ignored. 4. The Trash Link Relation This specification registers a new "trash" link relation to the Atom Registry of Link Relations defined in Section 7.1 of [RFC4287]. When appearing on atom:link elements within either the atom:feed or atom: source elements, The "trash" rel attribute value signifies that the IRI in the value of href attribute identifies a resource listing entries that have been deleted from the Feed document. If the linked resource is an Atom Feed Document, each of the entries in that feed will contain copies of the atom:entry elements removed from the feed Snell Expires July 7, 2008 [Page 4] Internet-Draft Atom Tombstones January 2008 containing the trash links. For example, ... ... A single linked trash resource may list entries deleted from multiple feed documents. In such cases, each entry in the trash resource SHOULD reference the feed from which the entry was removed. For instance, if the trash resource is an Atom Feed Document, each entry would contain an atom:source element identifying the feed the entry was deleted from. Linked "trash" resources are orthogonal to the at:deleted-entry element and are intended to provide servers with a way of allowing clients to recover deleted entries. For instance, the entries in a feed may be managed by two separate authors, one of whom may delete an entry that the other author wishes to later recover. If a trash feed is provided, the second author can look for a copy of the deleted entry there. While it will be common for servers to provide only a single trash resource per feed, or to have multiple feeds share a single trash resource, it is possible for a single feed to contain multiple trash links. The relationship between multiple trash links is undefined. Individual entries deleted from the feed containing the linked trash resources MAY appear in any, all or none of the linked trash resources. It is up to the server implementation to decide whether to provide a trash resource and whether or not to add deleted entries to those resources. 5. Security Considerations As specified in [RFC4287], Atom processors should be aware of the potential for spoofing attacks where an attacker publishes atom:entry or atom:deleted-entry elements using the same atom:id values as entries from other Atom feeds. An attacker may attempt to trick an application into believing that a given entry has either been removed from or added to a feed. To mitigate this issue, Atom processors are advised to ignore atom:deleted-entry elements referencing entries that have not previously appeared within the containing Feed document and should take steps to verify the origin of the Atom feed before Snell Expires July 7, 2008 [Page 5] Internet-Draft Atom Tombstones January 2008 considering the entries to be removed. 6. IANA Considerations 6.1. The Link Relation Registration "Trash" Attribute Value: trash Description: An IRI of a resource listing deleted resources. When appearing within an atom:feed or atom:source elements, signifies that the IRI in the value of the href attribute identifies a resource listing entries that have been deleted from the Feed document. Expected display characteristics: Undefined; this relation can be used for background processing or to provide extended functionality without displaying its value. Security considerations: Automated agents should take care when this relation crosses administrative domains (e.g., the URI has a different authority than the current document). 7. Acknowledgements The author gratefully acknowledges the feedback from the members of the Atom Publishing Format and Protocol working group during the development of this specification. 8. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3339] Klyne, G., Ed. and C. Newman, "Date and Time on the Internet: Timestamps", RFC 3339, July 2002. [RFC4287] Nottingham, M., Ed. and R. Sayre, Ed., "The Atom Syndication Format", RFC 4287, December 2005. [W3C.REC-xml-names-19990114] Hollander, D., Layman, A., and T. Bray, "Namespaces in XML", World Wide Web Consortium FirstEdition REC-xml- names-19990114, January 1999, . Snell Expires July 7, 2008 [Page 6] Internet-Draft Atom Tombstones January 2008 Author's Address James M Snell Phone: Email: jasnell@gmail.com URI: http://snellspace.com Snell Expires July 7, 2008 [Page 7] Internet-Draft Atom Tombstones January 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). 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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Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Snell Expires July 7, 2008 [Page 8]