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> -----Original Message----- > From: Jeni Tennison [mailto:jeni@j...] > Sent: Monday, January 06, 2003 05:22 > To: Alessandro Triglia > Cc: '[XML-DEV]' > Subject: Re: 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/
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