DOCBOOK: another markup question -- multi-level exercises

ok, still from a newbie perspective as i work my way through
the docbook book -- is there a recommended markup for a set of
exercises at the end of a section, with possible sub parts to
each exercise?  

1.  blah blah

   a) part a
  
   b) part b

2.  woof woof ...

   a) part a
 
   b) more part b

... and so on.  i can see the outer list can be an ordered list,
but can i apply a collective numeration attribute on the entire
outer ordered list, such as Arabic/loweralpha, or must i set
the numeration attribute of loweralpha individually on each of
the sub lists?

  or is there a better way?  always looking for good advice,
especially if you can supply a pointer to a site with good
examples i can pilfer.

rday

Robert P. J. Day
Eno River Technologies, Chapel Hill NC
Unix, Linux and Open Source corporate training

http://www.linux-migration.org