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Re: DTDs don't have ID or IDREF elements so why does XMLSchema

• From: Michael Kay <mike@saxonica.com>
• To: Roger L Costello <costello@mitre.org>
• Date: Tue, 1 Mar 2022 23:52:57 +0000

Orthogonality, or to put it another way, avoiding arbitrary restrictions. If ID and IDREF are going to be among your set of data types, then why would you want to disallow people from using them on elements.

(Personally, I would have made "IDness" and "IDREFness" properties that are orthogonal to type. I can't see any good reason for disallowing IDs of type integer or date. But the SGML and DTD legacy weighed strongly on the XSD designers.)

Michael Kay
Saxonica

> On 1 Mar 2022, at 23:32, Roger L Costello <costello@mitre.org> wrote:
> 
> Hi Folks,
> 
> DTD only allows attributes to be of type ID and IDREF.
> 
> XML Schema allows both attributes and elements to be of type ID and IDREF. Why? Is there a compelling use case for declaring an element to be of type ID? Is there a compelling use case for declaring an element to be of type IDREF?
> 
> /Roger
> 
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• Follow-Ups:
  • Re: DTDs don't have ID or IDREF elements so why does XMLSchema?
    • From: Peter Flynn <peter@silmaril.ie>

• References:
  • DTDs don't have ID or IDREF elements so why does XML Schema?
    • From: Roger L Costello <costello@mitre.org>