updated SSA schema for the registry

[Markus Dolensky]

Hi Ray & Registry Providers,

Although it should be clear from the text let me emphasize that the 
order of compliance levels is

    { query << minimal << full }

and not {minimal,query,full} which is the order of their declaration. As 
a reminder, 'query' was invented to support existing services and to 
lower the hurdle for archives who cannot afford to implement data model 
mediation.

Hence, my plea to registry interface designers is to make service 
providers understand that 'minimal' is actually 'medium' compliant or 
data model compliant. (And since the respective standard document 
already uses the given terms the Schema has to stick to them 
consistently, sorry).

Many thanks,
Markus as SSA co-editor