Delta-like descriptions for Thiele 0.3 draft

Robert A. (Bob) Morris ram at CS.UMB.EDU
Mon Nov 6 11:49:40 CET 2000

We have a better grasp now of the id mechanisms and are thinking along
lines described briefly below. If any XMLers will be in Frankfurt, I'd
like to talk more about these lines.

I. A general question for comment

We think that Kevin's example 9 the <DESCRIPTION> is really meant to be


rather than


as written. That is, the features and values are *references* to
features given ID's in earlier elements. Thus in this case
such a description is equivalent to

  <FEATURE NAME="Habit">
  <FEATURE NAME="Stolons">

II. Global feature values (This may be a Delta question).

In 0.3's Examples 8 and 9 there do not seem to be any global feature
values. Instead, all possible values are completely local to
features. For example, can there be a list of feature values
containing both "present" and "absent" to which any feature can refer,
whether or not those values are in that feature's local list of
values? Or rather, must every feature that wishes to allow those
values name them in its list of possible values>

III. Unique ID's (Non XML hackers please avert your eyes).  We can not
see where XML-Schema Schema syntactically enforces uniqueness of
ID's. If this is so, ID uniqueness must either be ignored, enforced by
context, or enforced by semantics at processing time. For example, in
draft 0.3, several objects have id="1". The XPath function library is
strong enough to use an ID as key when its uniqueness is given only by
context as in Examples 8 and 9 in draft 0.3, but if we accept this
approach, will we end up with a Schema against which validity testing
is hard? OTOH, if we are wrong and XML-Schema Schema does enforce
global uniqueness of ID, then must we uniqify the proposal by encoding
the context in the ID itself? That seems fragile.

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