Use of Substitution groups?

["Hallam-Baker, Phillip" <pbaker@verisign.com>]

All,

	Starting from the core-schema-assertion-10.xsd proposal, I suggest
that we use substitution groups in place of the current mechanism.

[Incidentaly we have traced the cause of the previous problem, I was working
from the documents sent to me by Prateek which had <AttributeAssertion>
elements in the examples, it turned out that I had been sent an earlier
version of the document than the one that went to the list and had assumed
that the two were the same except for the Visio documents.]


The practical imporance of this is what the toplevel elements look like,
whether it should be

<Assertion xsi:type="AttributeAssertionType">
    ...

or

<AttributeAssertion>
    ...


In order to make this change we would have to add in the following element
definitions:

<element name="AuthenticationAssertion"
	type="saml:AuthenticationAssertionType"
	substitutionGroup="saml:Assertion"/>
<element name="AuthorizationDecisionAssertion"
	type="saml:AuthorizationDecisionAssertionType"
	substitutionGroup="saml:Assertion"/>
<element name="AttributeAssertion"
	type="saml:AttributeAssertionType"
	substitutionGroup="saml:Assertion"/>

[The condition type would also need modification to match, this would
involve promoting condition to a toplevel element first since substitution
groups have to be top level elements]

The one complication to extension is that the extension schema would have to
remember to include to include the line adding the element to the
substitution group.

On the plus side this would simplify DOM type programming since one can pull
out assertions of a particular type with a single selector rather than
having to first select on the element name and then filter on xsi:type.


		Phill



Phillip Hallam-Baker FBCS C.Eng.
Principal Scientist
VeriSign Inc.
pbaker@verisign.com
781 245 6996 x227

Phillip Hallam-Baker (E-mail).vcf