RE: specify element type depending of same element attribute value?

> First problem is related to case 
> when type of contents of a simple element (not containing nested
> element) is determined by this element attribute value.  

This is one of the most well-known restrictions in XML Schema. The type of
an element is determined solely by its element name (and perhaps the context
in which the element appears, and perhaps the xsi:type attribute). You can't
write content models that depend on the presence or value of an attribute.

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