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 <b.fallenstein&gmx.de>

Declaration of syntactic structure:

    The identifier structure is:

       urn:<assigned number>:<random number>[:<local part>]

    where <random number> 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 <local part> is an arbitrary string of characters allowed
    in a URN without escaping.

    The <random number> 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 <random number>
    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 <local part> 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 <random number> 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
    <random number> part as defined above. If local parts are used,
    the <random number> 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
    <local part>.

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)

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