graphic language for describing TopicMaps

Hi there,

I'm just writing a complete documentation about a content management 
system with topicmaps i builded. Therefore i have to describe a lot of 
topic maps and PSI sets.
When i had done this work with plain XML, i could describe the data 
structure with XSD. But since there is no TMCL i have to do it in a 
visual way with digrams.
But is there a standardised way of creating a digram which describes a 
topicmap or a topicmap typesystem which does not only include topics, it 
also includes association types with specified roles and cardinalities.
Should i use UML?
How are you guys describing your topicmaps? Are you using rectangles for 
topics and circles for associations, how do you show that something is 
scopeable?
thanx
stefan