Sequence in schema

[Huma]

Hello All,I am new with schema.In schema file i want to restrict that in my xml file artist either has a child fullname or combination of firstname and lastname in arbitrary order, but each just once.xml file is like this.<catalog><cd><artist>Huma Khan</artist><country>Pakistan</country></cd><cd><artist><firstname>mona</firstname><lastname>ali</lastname></artist><country>India</country></cd><cd><artist><lastname>Khan</lastname><firstname>Imran</firstname></artist><country>Pakistan</country></cd></catalog>How can i restrict this in schema file.Thanx in advanceHuma

[steve_marjoribanks]

This cannot be done simply by using the XML Schema langiage. Instead you have to use something like Schematron (do a google search) and use it within your schema