Question on DL negation

Dear All,

As I understand, most DL's do not allow for the negation of roles.

However, given a formula of the form R(x,y) (where R is some role), 
since this is equivalent to (R(x,y) & \top(y)) which could be negated as 
¬( R(x,y) & \top(y)), is it possible to effectively relax this 
constraint in some cases without affecting the logic?

I'm interested in rules that have a single role as the head, and 
negation of such heads would be useful...

Thanks,

Matt
-- 
http://acl.icnet.uk/~mw
http://adhominem.blogsome.com/
+44 (0)7834 899570