Re: arcs for locators with the same role

You might want to check the current WD (just released 1/20/00), which 
eliminates the XLinks-as-elements syntax (such as the xlink:extended and 
xlink:locator in your example).

That aside, note that while you can assign a role attribute to the parent 
extended-type element, THAT role has nothing to do with the from/to 
attributes on arc-type elements. The latter must match up (according to 
[3.1.4]) with the role attribute on a LOCATOR-type element in the same 
extended link definition. (This should probably be amended to match the 
roles of either locator-type OR resource-type elements, per a couple of 
messages posted to www-xml-linking-comments earlier this week.)

(And your P.S., wanting to put a role attribute on arcs -- you CAN put a 
role attribute on arc-type elements.)

I don't know if the example you posted -- the academic course catalog -- is 
the specific purpose of your application or just an example. As presented, 
yes, it appears to present a problem. Actually it looks to me like the 
application design would need work in this case, eliminating what seem to 
be XLink problems. For example, the parent of the extended-type element 
would presumably be course info. Therefore, the only courses listed in the 
extended link group would be prerequisites for THAT course. Or (if all the 
course-info records were in the same document) you could have a "prereqs" 
attribute of type IDREFS on the main course element, eliminating all XLinks 
(at least to external documents).

Just a suggestion!