[
Lists Home |
Date Index |
Thread Index
]
> -----Original Message-----
> From: Jeni Tennison [mailto:jeni@jenitennison.com]
> Sent: Monday, January 06, 2003 05:22
> To: Alessandro Triglia
> Cc: '[XML-DEV]'
> Subject: Re: [xml-dev] Questions on XML Schema "all" and
> RELAX NG "interleave"
>
>
> Hi Alessandro,
>
> Henry Thompson wrote:
> >> The chances ought to be high if the <all> group is being used
> >> responsibly (which it often isn't, in my experience).
> Let's approach
> >> this from the other side -- if an element is declared to
> contain a,
> >> then b, then c as children, then the relative order of a,
> b and c in
> >> an instance carries no semantics. From this Occam suggests that in
> >> cases where there is no intention to convey different
> semantics with
> >> different order among siblings, a sequence should always
> be used, to
> >> avoid potential misunderstanding. _If_ this argument is
> persuasive,
> >> then you should _only_ use <all> when order _does_ matter,
> in which
> >> case re-arrangement changes the meaning of the document
> and should be
> >> avoided.
> [snip]
> > I would like to hear other people's views as well.
>
> I agree with Henry. To give an example, in RELAX NG, a common
> use for <interleave> is for mixed content. If you imagine:
>
> <p>
> A paragraph with <em>emphasised</em> text.
> </p>
>
> with the simple schema:
>
> element p { text & em* }
>
> it would be very wrong to move the <em> element to the start
> of the paragraph -- it would change the meaning of the document.
>
> There's a distinction between whether the order of elements is
> *constrained* and whether their order is *significant*. all
> and interleave simply indicate that the order is
> unconstrained, they say nothing about whether the order is
> significant. Unfortunately we use "matters" when talking
> about both of these.
By the way, I have read somewhere about a suggestion to extend <all> to
allow any maxOccurs in the next version of XML Schema.
Is this likely to happen?
Alessandro
>
> See also Tommie Usdin's paper from Extreme last year:
>
http://www.idealliance.org/papers/extreme02/html/2002/Usdin01/EML2002Usd
in01.html
which is a great read on precisely this topic.
Cheers,
Jeni
---
Jeni Tennison
http://www.jenitennison.com/
|
