Re: [xml-dev] DTD vs XSD: No Duplicate Types in (Mixed) Content Models

[=?UTF-8?B?TWFpayBTdMO8aHJlbmJlcmc=?= <maik.stuehrenberg@uni-bielefeld.de>]

Hi Ken,

thanks for your answer, I comment inline below.

Am 31.01.11 14:36, schrieb G. Ken Holman:
> At 2011-01-31 13:56 +0100, Maik Stührenberg wrote:
>> One of my students asked me if it wouldn't be easy to simulate XML
>> Schema's minOccurs and maxOccurs by repeating the same element type
>> (element name) in the content model of its parent element, e.g.:
>>
>> <!ELEMENT a (b, b, b)>
>> <!ELEMENT b EMPTY>
>
> ...
>
>> All three solutions were tolerated by the parsers I've tried. For
>> simulating minOccurs="3", maxOccurs="5" one could use the following
>> DTD solution:
>>
>> <!ELEMENT a (b, b, b, b?, b?)>
>> <!ELEMENT b EMPTY>
>>
>> To my suprise, I had no problems with the parsers I've tried.
>
> That surprises me as well, for the very reason you cited:
>
>> The interesting case is, if I have exact four occurrences of the
>> element b in an instance, resulting that my parser cannot know which b
>> in the model is being matched.
>
> Exactly.
>
>> Was this behaviour expected?
>
> Yes, I believe so, because of the ambiguous particles ... which way to go.

But when in mixed content models duplicate types are not allowed -- why 
are they allowed in element content models? The additional #PCDATA of a 
mixed content model should have only little effect on the question of 
determinism, or do I forget anything (maybe the whitespace characters 
that are allowed...)?
>
> But have you tried, for minOccurs="3" and maxOccurs="5" the W3C Schema
> equivalent of the following:
>
> <!ELEMENT a (b, b, b, (b, b?)?)>
>
> That combination is not ambiguous but gives you what you want. There is
> no doubt which of the <b> elements is being encountered.

Just for clarification: There is no specific DTD or content model that I 
need or want, I just stumbled upon this different behaviour of DTDs and 
XSDs when my student asked about it.
But your declaration is (of course) accepted by the parser because it is 
non-ambiguous. However, the question remains: why is the original

<!ELEMENT a (b, b, b, b?, b?)>

valid, too?

Again, thanks for your input.

Best,

Maik

>
> I hope this helps.
>
> . . . . . . . . Ken
>
> --
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-- 

Maik Stührenberg, M.A.

Universität Bielefeld
Fakultät für Linguistik und Literaturwissenschaft
Universitätsstraße 25
33615 Bielefeld

Telefon: +49 (0)521/106-2534
E-Mail: maik.stuehrenberg@uni-bielefeld.de

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