INTERNET--DRAFT Chris Weider IETF URI Working Group Merit Network, Inc. Peter Deutsch Bunyip Information Systems, Inc. May, 1993 Uniform Resource Names Status of this Memo In this paper, the authors propose an identifier, call the Uniform Resource Name (URN), which is designed to provide persistent naming for resources and objects on the Internet. This document is an Internet Draft. 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. Internet Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet Drafts as reference material or to cite them other than as a "working draft" or "work in progress." Please check the I-D abstract listing contained in each Internet Draft directory to learn the current status of this or any other Internet Draft. This Internet Draft expires November 10, 1993. 1: Introduction A Uniform Resource Name (URN) is an identifier which can be used to uniquely identify a resource, and is designed to provide persistent naming for networked objects. This name would stay the same no matter what the current location(s) of the object was. 2: Motivation This work comes out of the discussions held at the Uniform Resource Identifier meetings at the IETF, and from further discussions among interested parties. Currently, the only standard identification scheme for resources on the Net is the Uniform Resource Locator (URL) [Berners-Lee 1993]. This "Locator" is designed to provide a uniform way of specifying location and retrieval information for networked objects. The URL, however, will not provide a stable, long-lived reference to a resource as the resources have a bad habit of moving out from under the locator. Also, a given resource may have multiple URLs if it resides at a number of different locations on the net, or is available under a number of different access methods. Thus it is difficult to tell, given two different URLs, whether the resources they point to are the same or different without retrieving both of them. The Uniform Resource Name, or URN, has been designed to alleviate these problems. 3: The Uniform Resource Name (URN) 3.1 Functionality The URN is designed to provide persistent naming for objects on the net. It is intended to be used in conjunction with a directory service, which can provide a URN -> URL mapping [Weider 1993]. This URN-URL architecture allows permanent references to be made to resources without worrying about their current locations. It is also intended to provide some detection of duplicates in responses to queries of various resource location services. INTERNET--DRAFT Uniform Resource Names Weider, Deutsch 3.2 What URNs are *not* URNs are not intended to be human-readable in the sense that a human could look at the URN and determine anything about the contents of the resource. While the Naming Authority (q.v.) has the final determination of the contents (subject to the syntax constraints), the Naming Authority is STRONGLY discouraged from placing metainformation about the resource into the resource's URN, as the URNs are not expected to be read, and because this paper will specify only four consistent components of the URN. Although there have been a number of proposals placing extensive semantics on the contents of the URN [Spero 1992, Kunze 1993], it was decided by the authors of all the proposals that all metainformation should be conveyed using another mechanism, and that the Naming Authority should assume that humans will never look at the contents of the URN to determine qualities of the resource they are retrieving, and would not be required to guess from a given URN the URN of a document which might be related. 3.3 Components of the URN There are three components to the URN; a wrapper, a Naming Authority identifier, and an opaque 'name'. The general syntax is: URN:Naming_Authority_identifier::opaque_string::: ^ | ^ | ^ |_________________ wrapper ___|_______________| Blanks, s, and non-printing characters are NOT allowed. For a full allowable character set, see section 5. 3.3.1 The wrapper The wrapper consists of the 4 character header 'URN:', two consecutive colons to separate the Naming_Authority_Identifier component from the opaque_string component, and the 3 character trailer ':::'. 3.3.2 The Naming Authority Identifier The Naming Authority identifier consists of two sub-components, a 'scheme identifier' and an 'individual identifier'. A scheme identifier is the name of a protocol or organization which can guarantee the uniqueness and resolvability of the individual identifier. The individual identifier is the identifier of an organization which has assigned the opaque string component to the resource and can resolve the URN to a set of URLs for the resource. The scheme identifier and the individual identifier are separated by a colon. For example, typical Naming Authorities might be IANA:42117 or ISBN_Publisher_ID:0_201_12 etc. 3.3.3 The Opaque String The opaque string component of the URN is any string the Naming Authority wishes to assign to a given resource, subject only to the syntax description INTERNET--DRAFT Uniform Resource Names Weider, Deutsch below. As mentioned above, the Naming Authority should not assume that a human will ever read the URN. Also, the Naming Authority, in assigning an opaque string to a given resource, should keep the following guidelines in mind: 1: A given opaque string should be case-insensitive (for compatibility with very old systems). 2: A given opaque string, once assigned, should never be reused. These are expected to be persistent names for resources (think in terms of decades). 3: In assigning an opaque string, and thus creating a URN, the Naming Authority should make provisions for a URN -> URL mapping function. This need be nothing more than finding an organization which is already providing this service for other URNs and making arrangements to have them translate for the new URN, or could be as involved as creating a new software agent to provide this service. Remember that a name is no good without some way of getting a location. 4: URNs will be returned as pointers from a resource location service. (See [Weider 1993]). Consequently, a Naming Authority should give some thought to the assignation of new URNs for resources which are derived in some fashion from other resources to which that Authority has already assigned URNs. For example, should the Postscript version and the ASCII version of a paper have the same URN? While there are no universally applicable answers to questions like these (for example, should the Russian and English versions of a scientific paper have the same URN?) an Authority should keep in mind that users will want to weed out duplicate resources in the lists of URNs returned by a resource location service, and consequently will be doing a lot of equality testing on the URNs. 4: Setting up as a Naming Authority There are 2 scheme identifiers listed here; others will no doubt be suggested and added as this draft circulates. They are: IANA ISBN_Publisher_ID To set one's organization up as a Naming Authority, one can use the ISBN publisher ID one has been assigned, or one can apply for an Enterprise Number from the IANA (Internet Assigned Number Authority) if the organization does not already have one. The general syntax is listed in section 5. 5: Syntax Below is a BNF like description of the syntax of the URN. Spaces have been used here to separate components for readability, spaces are NOT ALLOWED in a syntactically correct URN. Square brackets '[' and ']' are used to indicate optional parts; a vertical line "|" indicates alternatives. Single letters and digits stand for themselves. All words of more than one letter are either expanded further in the syntax or represent themselves. INTERNET--DRAFT Uniform Resource Names Weider, Deutsch urn URN: Authority_Id :: opaque_string ::: Authority_Id Scheme_ID [ : Individual ] Scheme_ID IANA | ISBN_Publisher_ID Individual xalphas opaque_string xalphas xalphas xalpha [ xalphas ] xalpha a | b | c | d | e | f | g | h | i | j | k | l | m | n | o | p | q | r | s | t | u | v | w | x | y | z | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 0 | - | _ | . | @ 6: References [Kunze 1993] Kunze, John, Resource Citations for Electronic Discovery and Retrieval, March, 1993. Circulated to ietf-uri mailing list. [Spero 1992] Spero, Simon, Uniform Resource Numbers, November 1992. Circulated to ietf-uri mailing list. [Weider 1993] Weider, Chris and Deutsch, Peter. A Vision of an Integrated Internet Information Service, March, 1993. Available as ftp://nic.merit.edu/documents/internet-drafts/draft-ietf-iiir-vision-00.txt 7: Author's addresses Chris Weider clw@merit.edu Merit Network, Inc. 2901 Hubbard, Pod G Ann Arbor, MI 48109 Phone: (313) 747-2730 Fax: (313) 747-3185 Peter Deutsch peterd@bunyip.com Bunyip Information Systems 310 St-Catherine St West suite 202, Montreal, Quebec H2X 2A1 CANADA