"uid" microformats? (was Re: [uf-discuss] ISBN mark-up)

Xiaoming Liu liu_x at lanl.gov
Tue Apr 25 12:01:32 PDT 2006

On Tue, 25 Apr 2006, Tantek Çelik wrote:

> Please list the specific problems you've found with UID or URL, so we can
> make sure they are documented and properly explored/resolved.

Thanks for taking into consideration.

First hopefully we all agree on the problem to be addressed here, I think 
it is "a microformat for indicating something *is* an identifier", and I 
will presume there are three possible solutions: URL, UID, URI.

URL is good and I agree we should choose to resolvable URLs if possible. 
However URL identifies a resource via a network location, thus limits its 
scope, many well-established identifiers are not based on URL. e.g. In a 
typical library application, we really want to identify the books in 
Amazon and local catalog are referencing same thing, and the most 
promising means is by ISBN number.

UID might be good in their original scope (vcard and iCalendar), but I am 
afraid it is not sufficient for a wider scope, both semantically and 

In rfc2426 (vcard), UID is defined as:

Type name: UID
Type purpose: To specify a value that represents a globally unique
    identifier corresponding to the individual or resource associated
    with the vCard.
Type value: A single text value.

In rfc 2445 (iCalendar), UID is defined as:
Property Name: UID
Purpose: This property defines the persistent, globally unique
    identifier for the calendar component.
Value Type: TEXT

Semantically, while the definition is perfectly OK in original context, it 
may deserve consideration in a wider scope of defining an identifier 
microformat, "globally unique" or "persistent" are not necessarily 
applying to many established identifiers, are we going to exclude these 
"non-persistent" or "non-globally unique" identifiers? or we need to 
re-define UID in the context of identifier microformat?

Syntactically, I think microformats might want to encourage to use both 
standard classes and values, e.g. in hCalendar "dstart" and ISO8601 format 
is suggested, such as:  <abbr class="dtstart" title="2005-10-05">October 
5</abbr>, similarly, in an "identifier microformat" you may also want to 
encourage standard value to be used to allow interoperability. While UID 
allows *any* text value, there are good practices of URI schemes and 

I believe the syntax issue is rather important, because without clear 
specification, all kinds of things can be stuffed in, therefore defeating 
the purpose of interoperability, as illustrated by DOI/ISBN examples in 

URI is well defined, its semantic and syntax are easily accessible. And it 
is the very foundation of semantic web and RDF, I think introduction of 
URI fit nicely with other parts of semantic web. Although URI may add a 
new term to microformat, IMHO the benefit outweighs this drawback.


[1] http://microformats.org/wiki/uid-examples

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