Why is ID of type ID, whereas InResponseTo is of type NCName? And why is AssertionIDRef of type NCName?

["Costello, Roger L." <costello@mitre.org>]

Hi Folks,

 

In saml-schema-assertion-2.0.xsd it defines:

 

-        The ID attribute to be of type ID

-        The InResponseTo attribute to be of type NCName

-        The AssertionIDRef element to be of type NCName

 

I thought that ID, InResponseTo, and AssertionIDRef all contain the same type of value? 

 

The value of InResponseTo must equal the value of an ID, and the value of AssertionIDRef must equal the value of an ID, right?

 

If so, then why are they declared to be of different types?

 

/Roger