1. What is a unique identifier?
  2. What is the spec for a unique identifier to be used in an ExtensionModule?

What is a unique identifier?

This page describes what a unique identifier is in general and (more importantly), how it pertains to a WellFormedEntry

A unique identifier is a piece of data that unequivocally identifies something. On the Web, a URI is used as a unique identifier. A 128-bit GloballyUniqueIdentifier (GUID) is also common for software.

[BillKearney] unique identifiers can be found in things like SMTP and NNTP messaging systems. They're unique within the context of the service itself. As in as a UID for a message. In an SMTP context this is message number '342535235' from a FQDN host named 'server/'. There's no defined retrieval mechanism for SMTP. But that same sort of string used on an NNTP message can well be used to retrieve it. Contacting that same server, via NNTP protocols, would allow you to request that unique message. Neither of these formats have anything other than a limited set of characters that are allowed in the identifier. It's up to the machine in question to establish it's own uniqueness (and this IS mandatory). So if a weblog entry is going to possess an identifier it behooves us to ask what is that identifier going to facilitate? If it's going to facilitate later retrieval of the item then a discusson should be had on the merits of making the identifier unique to a transport or more universally usable. There's nothing about an HTTP style URL that requires that transport to be the only one used. It's perfectly fine to use an http:// URL in other transports. It'd be up to those transports to resolve how they'd obtain the item in question.

[JonathanSmith] Hopefully, the new format will avoid some of the problems reported [WWW]here with GUID in RSS.

[AsbjornUlsberg] Atom must provide a system for unique identifiers. I think the proposal of using [WWW]"The 'tag' URI scheme" (e.g.:,2003:8:042) is a good idea.

What is the spec for a unique identifier to be used in an ExtensionModule?

Why not just use the a namespace to uniquely identify a module? Namespaces are unique, easy to implement and XML.

[AsbjornUlsberg] Sounds like a good idea.

See ExtensionModule