Namespace ID:  urn-7

Registration Information:
   Registration version: 1; registration date: 2009-03-22

Declared registrant of the namespace:  3GPP Specifications Manager
   (3gppContact&etsi.org) (+33 (0)492944200)

Declaration of syntactic structure:  The URN consists of a
   hierarchical service identifier or application identifier, with a
   sequence of labels separated by periods.  The leftmost label is
   the most significant one and is called 'top-level service
   identifier', while names to the right are called 'subservices' or
   'sub-applications'.  The set of allowable characters is the same
   as that for domain names (see RFC 1123 [RFC1123]) and a subset of
   the labels allowed in RFC 3958 [RFC3958].  Labels are case-
   insensitive and MUST be specified in all lowercase.  For any given
   service identifier, labels can be removed right-to-left and the
   resulting URN is still valid, referring a more generic service,
   with the exception of the top-level service identifier and
   possibly the first subservice or sub-application identifier.
   Labels cannot be removed beyond a defined basic service; for
   example, the label w.x may define a service, but the label w may
   only define an assignment authority for assigning subsequent
   values and not define a service in its own right.  In other words,
   if a service identifier 'w.x.y.z' exists, the URNs 'w.x' and
   'w.x.y' are also valid service identifiers, but w may not be a
   valid service identifier if it merely defines who is responsible
   for defining x.

     Service-ID      = "urn:urn-7:" urn-service-id
     urn-service-id  = top-level *("." sub-service-id)
     top-level       = let-dig [ *26let-dig ]
     sub-service-id  = let-dig [ *let-dig ]
     let-dig         = ALPHA / DIGIT / "-"

   While the naming convention above uses the term "service", all the
   constructs are equally applicable to identifying applications
   within the UA.

Relevant ancillary documentation:  None

Identifier uniqueness considerations:  A service identifier
   identifies a service, and an application identifier an application
   indicated in the service or application registration (see IANA
   Considerations ([RFC6050], Section 8)).  Uniqueness is guaranteed 
   by the IANA registration.

Identifier persistence considerations:  The service or application
   identifier for the same service or application is expected to be
   persistent, although there naturally cannot be a guarantee that a
   particular service will continue to be available globally or at
   all times.

Process of identifier assignment:  The process of identifier
   assignment is described in the IANA Considerations (RFC6050], 
   Section 8).

Process for identifier resolution:  There is no single global
   resolution service for service identifiers or application
   identifiers.

Rules for lexical equivalence:  'service' identifiers are compared
   according to case-insensitive string equality.

Conformance with URN syntax:  The BNF in the 'Declaration of
   syntactic structure' above constrains the syntax for this URN
   scheme.

Validation mechanism:  Validation determines whether a given string
   is currently a validly assigned URN (see RFC 3406 [RFC3406]).  Due
   to the distributed nature of usage and since not all services are
   available everywhere, validation in this sense is not possible.

Scope:  The scope for this URN can be local to a single domain, or
   may be more widely used.