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Subject: Re: [emergency] Unique Identifiers Discussion: Seehttp://taguri.org
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:
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