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RE: b*c*b*c* vs. (b*c*)^2,2

From: Torsten Grust <Torsten.Grust@uni-konstanz.de>
Date: Thu, 12 Feb 2004 13:23:04 +0100
Message-ID: <16427.28712.444358.913416@gargle.gargle.HOWL>
To: "Michael Kay" <mhk@mhk.me.uk>
Cc: <xmlschema-dev@w3.org>

Thanks Henry and Michael for these quick and very helpful responses.

Only to double-check that I am on the right track now: from your
answers I take it that the XML Schema Unique Particle Attribution
constraint is the same concept as ``weak unambiguity'' (as defined in
Anne Brueggemann-Klein's papers).  To paraphrase Anne:

   If a regular expression E is weakly unambigious, we may attach
   semantic actions to occurrences of symbols in E and then observe
   a unambigious correspondence between the letters matched by E and
   those actions.

(Which, for example, an XML Schema processor could use during
validation to attach type annotations to XML element nodes.)

Does this make sense?

Again, thanks a lot.

On February 12 (10:47 -0000), Michael Kay wrote with possible deletions:
| I think the confusion is due to the technical use of the term
| "ambiguity".
| In popular language, it's completely clear which set of strings the
| expression b*c*b*c* matches. The "ambiguity" is because the system
| (unlike the user) doesn't just want to know whether a string matches the
| sequence, it wants to know which particle each of the input elements
| matches, and there are two (or three?) possible different ways of
| matching the input bc.
| When you write it as (b*c*) there are only two particles and so the
| system knows which particle matches each input element.
| An interesting example, though!

  | Dr. Torsten Grust                          Torsten.Grust@uni-konstanz.de |
  |                                   http://www.inf.uni-konstanz.de/~grust/ |
  | Database Research Group, University of Konstanz (Lake Constance/Germany) |
  |             (Please avoid sending me MS Word or PowerPoint attachments.) |
Received on Thursday, 12 February 2004 07:23:34 UTC

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