| Re: Required 'id' attributes (was: More detailed 'speed change' definitions) [message #1126 is a reply to message #1125] |
Thu, 08 November 2012 20:52   |
Dirk Bräuer
Messages: 311
Registered: August 2008
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Senior Member |
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Dear Susanne,
thank you for the reply.
Some of the aspects on 'id's in RailML
> * There are other often-used XML standards that use the same mechanism:
Yes, of course, all strict-relational data models do so.
(Strict-relational data models need to have Id's.)
In RailML, we also have some hierarchy (so RailML is not
strict-relational) and, more important, we do not know about the data
model of the reading/writing software. So I would say it is bad to force
it to strict-relational data models.
Additionally, we do not have 'id's at each <elements>, so the selection of
elements with id (out of all elements) is a rather arbitrary one. If your
arguments would be accepted: Wouldn't we need to provide 'id's at all
<elements>, would we?
So to come out of this current "arbitrariness" I thought about the rule
"no 'id' without a 'ref' to it". So: If we need a reference, we have to
provide both 'id' and 'ref'.
That would lead us to a rather logic structure: Hierarchy (<elements>)
combined with non-hierarchic references with 'id's.
The question on the meaning of 'id's in RailML (as a primary key for
relational data models) is a more general one - not specially on speed
changes, so I will end this arguing here and open a new topic at "misc".
Best regards,
Dirk.
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