From an interval constraint graph one can  derive  some  directed
acyclic   graphs   which   bear useful semantics - like plausible
causal chains and containment hierarchy. These constraints belong
to  tractable  sub-algebras  of the interval algebra. Thus, apart
from being interesting from the practical point  of  views   they
are efficient  for  reasoning purposes. I have investigated these
sub- algebras and developed efficient algorithms  for  them.  The
work  has  a  much  broader  scope  within  the  general  area of
constraint propagation than just for reasoning with the  interval
algebra. For example, traditionally CSP algorithms only check for
consistency or find a solution if one exists.  My  work  in  this
area   may   be   extended  in  detecting  plausible  sources  of
inconsistency.  This problem has never been addressed before.