Hi there,
The schema which you supplied contains no structure just a list of global elements. The error comes about because the tsd:which element must point to a valid path and “” is not valid. So probably the tsd:which element could be removed.
(Btw just a Forum tip for the day: its best to add new topics rather than Poll Questions) 
Regards,
Stuart Fyffe-Collins
Software AG (UK) Ltd.
#API-Management#Tamino#webMethods