[sc34wg3] XTM 2.0 topicRef - proposal for an erratum

[Lars Heuer]

Hi all,

I found more issues regarding XTM 2.0. XTM 2.0 enforces that topics
have at least one item identifier (the id attribute) which is no
requirement of the TMDM.

Further, I think it was a mistake to remove the possibility to
reference a topic by its subject identifier / subject locator. In XTM
1.0 we have the possibility to reference a topic by its subject
identifier / subject locator, while XTM 2.0 enforces (again) item
identifiers.

I think this item-identifier-philia of XTM 2.0 has to be fixed. No
other, modern Topic Maps syntax requires that many item identifiers.

I've attached a RELAX-NG scheme for a XTM version that is (differently
to the proposal [1]) backwards compatible to XTM 2.0. Any XTM 2.0
topic map can be parsed the the proposed XTM 2.1 version.

Short summary of changes:
* Introduction of a subjectLocatorRef and subjectIdentifierRef element
  that can be used everywhere where a topicRef element can be used
* The topic id is optional in cases where at least one item
  identifier, subject identifier or subject locator is provided
* Added a reifier element that provides the possibility to reference a
  topic by its item identifier, subject identifier, or subject locator
  (note, that the 'reifier' attribute is kept for backward
  compatibility)
* The value "2.1" is allowed in the version attribute of the topicMap
  element

The proposed changes require a minimum modification of a XTM 2.0
compatible parser and would be more TMDM compatible than the current
XTM 2.0 version.


[1] The case for XTM 3.0 <http://tmra.de/2008/talks/pdf/121-135.pdf>

Best regards,
Lars
-- 
Semagia 
<http://www.semagia.com>
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