Schemas and Other Crucial XML Questions

Sam Gentile samg at
Mon Aug 10 16:14:41 BST 1998

Thanks for your answers. I'm still a little confused.

 > > We have a spec called "XML-Data W3C Note 05 Jan 1998", which
 > > discusses schemas. It is not clear from the document what a
 > > schema is used for or what it's purpose is. Is it for designing
 > > the XML buffer only or is it read by the parser? Is it an
 > > extension to XML? Are they even necessary in basic XML?

>>>XML-Data is a note that was submitted to the W3C by Microsoft and a
>>>couple of partners -- it has no official status (a W3C "Note" means
>>>roughly "here's a neat idea from one of our members").

Ok, that's clear.

>>XML 1.0 DTDs and proposed replacements/enhancements such as
>>Microsoft's XML-Data and XML-Dev's XSchema perform three distinct

>>1. Provide a schema for validating the *logical structure*
>>   (element/attribute/data) structure of an XML document; as a side
>>   effect, structural schemas can also provide enough information to
>>   control a guided XML authoring tool.

How is this different from what DTDs do? Don't DTDs validate the *logical
structure* of an XML document?

>>2. Declare the entities (internal strings or external objects) that
>>   make up the *physical structure* of an XML document.

Don't DTDs do this?

3. Provide default logical content for an XML document (such as
   default values for attributes, though XML-Data goes further).

Some people have argued -- quite convincingly, I think -- that these
roles should be kept separate: they are mixed together right now for
historical compatibility with ISO 8879:1986 DTDs.

How about the question of namespaces? Is this legal XML?

or do you need namespaces?


Sam Gentile

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