To provide some context and background on the discussion during
today’s call concerning unique identifiers, I would like to suggest that
CAP folk become familiar with the “tag” URI scheme. Documentation
can be found at:
http://taguri.org/
Tag URI is currently documented as an Internet Draft;
however, it has been accepted for publishing as an RFC. When the RFC is issued,
the ID will become obsolete although the RFC will contain substantially the
same text as the current draft of the ID. The ID is temporarily available as: http://taguri.org/07/draft-kindberg-tag-uri-07.html
A sample “tag-uri” looks like: tag:hawke.org,2001-06-05:Taiko
This
URI, and others which are assigned using the tag uri scheme, is unique across
all time.
An
approach similar to the Tag URI has been used by the Newspaper industry in the
definition of the NewsML URN’s (URN = Uniform Resource Name) that are
used in identifying news content. For more information on the NewsML URN
scheme, see: http://ietf.org/rfc/rfc3085.txt
A sample NewsML URN is: urn:newsml:iptc.org:20001006:NewsMLv1.0:1
Like
Tag URI’s, NewsML URN’s are unique across all time. Both of these
schemes use the basic idea that a unique identifier is a sequence of three
parts:
1.
A string which is “owned” at some
specific time by the creator of the identifier and is guaranteed not to be
assigned or owned by more than one administrative entity at any one time. (But,
whose ownership might change over time)
2.
A timestamp that identifies a point in time or
period of time during which the creator of the identifier actually “owned”
the string.
3.
Some value which is unique among all those used
by this particular creator in combination with 1 and 2 above.
If
CAP reference ids are constructed in the following manner: (partial ABNF
below):
CAP-reference
= sender “,” sent “,” identifier
And,
if sender is either a domain name or something like an email address that
incorporates a domain name, then Cap-references could be guaranteed to be
globally unique – across all time.
Given
the discussion above, I would suggest we might want to register a CAP URN
scheme with IANA. Such an URN might then have the following form:
CAP-URN
= “cap:” sender “,” sent “,” identifier
bob
wyman