RE: Use of global attrbutes

> If a global attribute is declared in an XSD file, then in an 
> XML instance conforming to that XSD is it automatically valid 
> for an instance of that global attribute to appear in any 
> instance of a complex type,

No.

 or is it necessary for the XSD to 
> define an attribute use of the global attribute within the 
> complex type definition.

Yes. Though it's often done using a wildcard (x:anyAttribute).

Michael Kay
http://www.saxonica.com/