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Re: Constrain the Number of Occurrences of Elements in your XM

• To: "'greg@f...'" <greg@f...>
• Subject: Re: Constrain the Number of Occurrences of Elements in your XML Schema
• From: James Lindley Walford <jlw@i...>
• Date: Mon, 8 Aug 2005 10:40:26 +0200
• Cc: "'xml-dev@l...'" <xml-dev@l...>

>Who pays and how do the diagnostics help with the
>money?  Do you say to the client "well, someone sent us a document that
>was too big so you don't get to penalise us"?  They may say "it wasn't
>us so we don't care".  They may just laugh and walk away.  They may say
>"we sent you a document this big during testing and it validates against
>your schema", and then laugh and walk away. 

Is this not merely an example of trying to do too much with XML Schema?
There are many things that XML Schema can't do that might be considered
business critical - e.g. context dependent validation (so we use Schematron
instead). XML Schema isn't the only layer in validation and processing, nor
should it be regarded as such.

In my opinion this is a common feature of how many people view XML schema.
Almost every day I meet people that assume that the ability of XML (and
therefore XML Schema) to use human readable tag names equates to XML Schema
being self-documenting, that no external data is necessary to aid
understanding of it. So not only is a schema being used in a validation
layer, it's also being used the entire documentation of the XML format tghat
it is to validate. This is simply put, abuse of XML.

Legal issues regarding financial responsibility for a software failure are
not the sort of things that XML Schema is designed to govern. Put that in a
contract.

If you need to place an arbitrary limit on the size of the XML exchanged and
processed then that should also be done elsewhere. If it really seems
important that such information is published via a schema then put it in a
comment <!-- Please don't send us files larger than 1GB as we can't process
them efficiently --> Let XML Schema do the job its designed for: primarily
validation of XML structure and content.

Just my tuppence worth...

James Walford

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