Uniform Resource Names (urnbis) J.C. Klensin Internet-Draft April 7, 2014 Updates: 3986 (if approved) Intended status: Standards Track Expires: October 07, 2014 Names are Not Locators and URNs are Not URIs draft-ietf-urnbis-urns-are-not-uris-00.txt Abstract Experience has shown that identifiers associated with persistent names are quite different from identifiers associated with the locations of objects. This is especially true when such names are are expected to be stable for a very long time or when they identify large and complex entities. In order to allow Uniform Resource Names (URNs) to evolve to meet the needs of the Informational Sciences community and other users, this specification separates the syntax for URNs from the generic syntax for Uniform Resource Identifiers (URIs) specified in RFC 3986, updating the latter specification accordingly. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on October 07, 2014. Copyright Notice Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Klensin Expires October 07, 2014 [Page 1] Internet-Draft URNs are not URIs April 2014 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. A perspective on locations and names . . . . . . . . . . . . . 2 3. Changes to RFC 3986 . . . . . . . . . . . . . . . . . . . . . 5 4. Other Required Actions . . . . . . . . . . . . . . . . . . . . 5 5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5 6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 5 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 8. Security Considerations . . . . . . . . . . . . . . . . . . . 6 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 9.1. Normative References . . . . . . . . . . . . . . . . . . . 6 9.2. Informative References . . . . . . . . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6 1. Introduction The Internet community now has many years of experience with both name-type identifiers (notably Uniform Resource Names (URNs [RFC2141] [RFC2141bis]) and location-based identifiers (notably Uniform Resource Locators (URLs) [RFC1738]). That experience leads to the conclusion that it is impractical to constrain URNs to the syntax and high-level semantics of URLs. Generalization from URLs to generic Uniform Resource Identifiers (URIs) [RFC3986], especially to name- based, high-stability, long-persistence, identifiers of the URN variety, has failed because the assumed similarities do not exist to a sufficient degree. Ultimately, locators, which typically depend on particular accessing protocols and a specification relative to some physical space or network topology, are simply different creatures from long-persistence, location-independent, object identifiers. The syntax and semantic constraints that are appropriate for locators are either irrelevant to or interfere with the needs of resource names as a class. That was tolerable as long as the URN system didn't need additional capabilities but experience since RFC 2141 was published has shown that they are, in fact, needed. This specification updates the Generic URI Syntax specification [RFC3986] to exclude URNs from its coverage. Put differently, with the publication of this specification, URNs are no longer considered a member of the class of URIs to which RFC 3986 applies. [[Note in draft: the above leaves it ambiguous as to whether it remains appropriate to call URNs "URIs". That ambiguity is intentional and, if possible should keep the question part of the "someone else's problem" category.]] For URLs and such other URIs as may exist or be created in the future, this specification does not change the syntax rules and other requirements and recommendations of RFC 3986. 2. A perspective on locations and names Klensin Expires October 07, 2014 [Page 2] Internet-Draft URNs are not URIs April 2014 Content industries (e.g., publishers) and memory organizations (e.g., libraries, archives, and museums) invest a lot of resources on naming things and the topics of naming and classification are important information science issues. Tens, if not hundreds, of millions of persistent identifiers have been assigned during the last decade. Several identifier systems have been developed for persistent and unique identification of resources. When there is a real need to preserve something important (such as scientific publications, research data, government publications, etc.) for the long term, URNs or other persistent identifiers are used; URLs (or other generic URIs) are not being used for identification or even linking purposes. Naming and locating e.g. library resources are both complex activities which have different aims. Traditionally, naming and locating resources have been separate activities, and the rules for the former are much more stringent than for the latter. The same principles are being applied to digital materials as well as more traditional ones. In a library, any book, be it printed or digital, has both unique and persistent International Standard Book Number (ISBN) and non-unique (each copy has its own location information) and short-lived location information which cannot be trusted in the long run. ISBN never changes, but both shelf locations and Web addresses usually do, many times during the book's life span. Giving location information a role in identification would not only force libraries to adopt different policies for printed and digital content, it would also undermine the value of existing identifier systems. Let us assume that ten people independently upload a copy of an electronic book into different locations in the Web. Are all these ten URLs valid identifiers of the book? And what is their relation to the ISBN or other identification information of the book such as its title? From the perspective of the communities who depend on persistent identifiers, critical issues include: 1. Resource identification has to be a managed process. Assigning URIs generally is not. Although it may be possible to introduce some level of control to URI assignment, a user cannot determine whether some URI is reliable or not. 2. Anyone may assign new URIs to resources even if these resources already have proper identifiers assigned to them. Claiming that these URIs actually identify something undermines the value of proper identifiers. 3. There is no 1:1 relation between the resource identified and URIs. An e-book in the Web may be represented as 1-n files (URIs), and a single file may contain several books. And books are simple, we need to name very complex objects such as research data sets, or some component parts within these complex data sets. Klensin Expires October 07, 2014 [Page 3] Internet-Draft URNs are not URIs April 2014 4. One resource such as a scientific article is typically available from multiple locations, including (for instance) the publisher's document supply service, a university's open repositories and other cooperative repository systems, legal deposit collections and the Internet archive. A resource should have one and only one identifier of a given type; URIs do not meet this requirement. 5. URIs relate to instances (copies) of resources, whereas traditionally identification has much broader scope. Identifiers may be assigned to, e.g., an immaterial work (such as Hamlet), its expressions (e.g. Finnish translation of Hamlet), and manifestations of works and expressions (e.g. PDF version of Finnish translation of Hamlet). 6. Over time, different resources (or different versions of the same resource) may be found from the same non-URN URI. A user has no way of knowing whether the resource has changed. One of the basic principles for proper identifier systems is that the same identifier is never assigned to another resource. In general, URIs do not meet this requirement. 7. Persistent identification must be available for resources which are available only in databases and other environments that are often identified today as "deep web". URIs for these resources tend to be very complicated and it will be difficult to keep them alive even with the help of DNS redirection when e.g. the underlying database management system changes. 8. The role URI fragment and query could or should have in identification is unclear and the statements in RFC 3986 are definitely problematic from the points of view of existing identifier systems and management of naming. Does fragment identify a location or a certain section of a resource? In the evolving set of URN Internet standards, fragment will not be a part of the Namespace Specific String. Then fragment only indicates a place / segment within the identified resource, but does not identify it. If fragment had a role in identification, fragments would extend the scope of existing standard identifiers to component parts of resources. For instance, anyone could use URN based on ISBN + fragment to identify chapters of electronic books. Things get even more complicated with query since what an identifier + query resolves to may not have anything to do with the original resource. For instance, URN based in ISBN + query may resolve to the metadata record describing the book. These records have their own identifiers which are not based on ISBNs. [[Note in draft: Most of the discussion above may belong in 2141bis rather than here.]] Klensin Expires October 07, 2014 [Page 4] Internet-Draft URNs are not URIs April 2014 9. For many organizations, persistence means decades or centuries. Anything that is protocol dependent will eventually fail. URLs do not change by themselves, but in the long run it is very difficult for people to not change them or the objects to which they point. The mention of centuries is intentional. Content industries, memory organizations (such as national and repository libraries and national archives) and universities and other research organizations, need identifiers that will persist for hundreds of years. Such identifiers might even need to outlast the institutions themselves, and definitely should be usable even if current technologies such as the Web and the Internet cease to exist or are supplanted by something new (as unlikely as that might seem today). In addition, operations on, or additional specifications about, names and the associated objects must be possible, as stable as the names themselves, and reasonably efficient. For example, if a URN were assigned to an encyclopedia that consisted of many volumes, it should be feasible to identify (and locate and retrieve if that were desired) a particular volume or even a particular article without accessing or retrieving the entire set. 3. Changes to RFC 3986 This specification removes URNs from the scope of RFC 3896. It makes no changes for URI types that remain within that scope. 4. Other Required Actions The basic URN syntax specification [RFC2141] was published well before RFC 3986 and therefore does not depend on it. Successors to that specification will need to fully spell out the syntax and semantics of URNs without generic or implicit reference to any URI specification. 5. Acknowledgments This specification was inspired by a search in the IETF URNBIS WG for other alternatives that would both satisfy the needs of persistent name-type identifiers and still fully conform to the specifications and intent of RFC 3986. That search lasted several years and considered many alternatives. Discussions with Leslie Daigle, Juha Hakala, Barry Leiba, Keith Moore, Andrew Newton, and Peter Saint- Andre during the last quarter of 2013 and the first quarter of 2014 were particularly helpful in getting to the conclusion that a conceptual separation of notions of location-based identifiers (e.g., URLs) and the types of persistent identifiers represented by URNs was necessary. Peter Saint-Andre provided significant text in a pre- publication review. 6. Contributors Klensin Expires October 07, 2014 [Page 5] Internet-Draft URNs are not URIs April 2014 Juha Hakala contributed most of the text of Section 2. Contact Information: Juha Hakala The National Library of Finland P.O. Box 15, Helsinki University Helsinki, MA FIN-00014 Finland Email: juha.hakala@helsinki.fi 7. IANA Considerations [[RFC Editor: Please remove this section before publication.]] This memo is not believed to require any action on IANA's part. In particular, we note that there are a collection of "Uniform Resource Identifier (URI) Schemes" that does not include URNs and a series of URN-specific registries that do not rely on the URI specificstions. 8. Security Considerations All drafts are required to have a security considerations section. 9. References 9.1. Normative References [RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997. [RFC3986] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, January 2005. 9.2. Informative References [DeterministicURI] Mazahir, O., Thaler, D. and G. Montenegro, "Deterministic URI Encoding", February 2014, . [RFC1738] Berners-Lee, T., Masinter, L. and M. McCahill, "Uniform Resource Locators (URL)", RFC 1738, December 1994. [RFC2141bis] Saint-Andre, P., "Uniform Resource Name (URN) Syntax", January 2014, . Author's Address Klensin Expires October 07, 2014 [Page 6] Internet-Draft URNs are not URIs April 2014 John C Klensin 1770 Massachusetts Ave, Ste 322 Cambridge, MA 02140 USA Phone: +1 617 245 1457 Email: john-ietf@jck.com Klensin Expires October 07, 2014 [Page 7]