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schema 1.1 request - drop numeric occurrence values on model groups

From: Xan Gregg <Xan.Gregg@jmp.com>
Date: Thu, 4 Dec 2003 13:14:56 -0500
Message-ID: <EFA630DC919FFE4BAF7E353ACB2C0AA10589332A@merc17.na.sas.com>
To: <www-xml-schema-comments@w3.org>
Cc: "Ashok Malhotra" <ashokma@microsoft.com>

Also known as "numeric exponents", when applied to model groups these 
cause inordinate complexity for subsumption testing on state machines
generated from content models.  Numeric exponents refer to occurrence
constraints besides 0, 1, and unbounded (the values supported natively
by regular expressions).

When asked, the WG members have been unable to point to a good use of
such occurrence values. Henry Thomspon has noted in [1] that of the 700
schemas contributed by XSV users, there was only one non-trivial use of
numeric exponents on a model group:

  <seq min=1 max=3>
   <elt min=0/>
   <elt min=0/>
   <elt min=0/>
  </seq>

For completeness, I have also noted one contrived case [2] that was found in
a tutorial:

sandwich ::=
    lower_slice 
    [ mustard | mayonnaise ]
    lettuce? tomato?
    [ bologna | salami | ham ] {2,4}
    cheese+
    top_slice

xan

[1] http://lists.w3.org/Archives/Member/w3c-xml-schema-ig/2001Nov/0042.html
[2] http://lists.w3.org/Archives/Member/w3c-xml-schema-ig/2002Feb/0079.html
Received on Thursday, 4 December 2003 13:17:59 UTC

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