[sc34wg3] CTM: Proposal for relaxing the restriction on start-character for topic-ID in CTM

Lars Heuer heuer at semagia.com
Mon Oct 26 12:52:09 EDT 2009

Hi Are,

> We are currently using the DNS-name as the topic identifier of a

> 3d-prod01.uio.no is a valid DNS-name, but is not a valid Topic ID in  
> LTM or CTM.
> Ref: http://www.isotopicmaps.org/ctm/ctm.html#sec-topic-identity

In CTM (I believe contrary to LTM), you can always use the following
syntax to allow topic identifiers that are used as keywords / would be
illegal as topic identifiers:

^<#topic-id-here> .

In your example you could write:

   ^<#3d-prod01.uio.no> - "3d-prod01.uio.no"; isa unix-server .

The ^ indicates that the following IRI reference should be interpreted
as item identifier. See also

But I wonder if using item identifiers makes sense in your use case.
Wouldn't it be much better to use a subject identifiers? Remember that
the topic identifiers are always resolved against the document IRI.

> - Are there any good reasons that a CTM-ID could not start with a
> number?

Yes, the ID production has the same constraints as the XML identifier
production. And if we'd allow the identifiers to start with a number,
how do we avoid that you'll use 42 as topic identifier? And how do we
distinguish your topic id "42" from the integer "42"?

Best regards,

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