Namespace ID: urn-5 Registration Information: Version 2 Date: 2003-05-06 Declared registrant of the namespace: Name: University of Jyväskylä Hyperstructure Group Address: Dept. of Mathematical Information Technology University of Jyväskylä PO. Box 35 (Agora) FIN-40014 Jyväskylä Finland Contact: B. Fallenstein Declaration of syntactic structure: The identifier structure is: urn::[:] where is a string consisting of at least 27 of the following characters: Lowercase (a-z) and uppercase (A-Z) letters, digits (0-9), the hyphen (-) and the plus sign (+). If present, the optional is an arbitrary string of characters allowed in a URN without escaping. The is a pseudo-random number (160 or more bits) encoded in base64 [RFC-2045]. As slashes (/) are not currently allowed as part of URNs, hyphens (-) are used instead. The padding character (=) is not used. (An earlier version of this specification allowed to be only 26 characters long, making for only 156 random bits. Such identifiers must still be recognized, but new identifiers should contain at least 27 random characters.) The is a counter, intended to allow re-use of a pseudo-random number; this allows a program to generate only one pseudo-random number per session, only incrementing a counter each time a new identifier is generated. Compression of documents containing many different identifiers of this form is improved if some of the identifiers share the part. Examples of possible URNs in this namespace include: urn:urn-n:-URS6S2A3+chjjHVlTkQ9KT5nu2 urn:urn-n:JtTCacwJ1e1N0yqTULRG7C1GLq8:4 urn:urn-n:Od4rB2QNOLt1e5wITWSJ+9U2Ve+Zon6N3d:17 (In these examples, urn-n is a placeholder for the namespace id to be assigned by IANA. The examples are not URNs in actual use.) Relevant ancillary documentation: RFC 2045 [RFC-2045] defines the base64 encoding. Note that the hyphen (-) is used instead of the slash (/). Identifier uniqueness considerations: Provided that the source of pseudo-random data used is good enough, it can be reasonably assumed that identifiers are unique (for example, SHA-1 [FIPS-180-1] also assumes uniqueness of 160 bit identifiers). Identifier persistence considerations: Users must not re-assign an identifier. This is not a problem, since they are free to create new identifiers at any time. Process of identifier assignment: Identifiers can be informally assigned by users at any time. There is no central authority assigning identifiers or specifying meaning for them. New identifiers are created when a user or program wants to name some entity globally without contacting a naming authority first. Examples include RDF resources [RDF] and XML namespace names [XML-namespaces]. Users specify meaning for identifiers by starting to use them, for example in an RDF graph. If local parts are not used, an identifier is created by generating 160 or more bits of pseudo-random data from a trusted source and encoding them in base64, using the characters allowable in the part as defined above. If local parts are used, the part is generated beforehand (usually when the program generating the identifiers is started, or when the first identifier in a particular session is created); each time a new identifier is needed, a counter is incremented and used as the . Process for identifier resolution: None specified. Note that the namespace is primarily meant for resources that are only named, not resolved (such as XML namespace names). Rules for Lexical Equivalence: The normal rules for lexical equivalence of URNs apply. Conformance with URN Syntax: No special considerations. Validation mechanism: The namespace-specific string (nss) must abide the following ABNF [RFC-2234] grammar: nss = random-number / (random-number ":" urn-string) random-number = 26*base64 urn-string = ALPHA / DIGIT / other base64 = ALPHA / DIGIT / "+" / "-" other = "(" / ")" / "+" / "," / "-" / "." / ":" / "=" / "@" / ";" / "$" / "_" / "!" / "*" / "'" For new identifiers, random-number must be at least 27 characters long. Scope: Global. References: [FIPS-180-1] NIST, FIPS PUB 180-1: Secure Hash Standard, April 1995. http://csrc.nist.gov/fips/fip180-1.txt (ascii) http://csrc.nist.gov/fips/fip180-1.ps (postscript) [RDF] RDF Model and Syntax. http://www.w3.org/TR/1999/REC-rdf-syntax-19990222 [RFC-2045] Freed, N., and Borenstein, N., "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996. [RFC-2234] Crocker, D., and Overell, P., "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. [XML-Namespaces] Namespaces in XML. http://www.w3.org/TR/1999/REC-xml-names-19990114 CHANGE HISTORY: From Version 1 to Version 2 -For new identifiers, 27 random characters (162 bits) rather than 26 characters (156 bits) are required. - "160 bytes" has been changed to "160 bits" in two places. - The notion that using the local part for anything but counting is 'strongly discouraged' has been removed. (created 2002-08-16) []