James F. Allen, ``Maintaining knowledge about temporal
intervals'', <I> Communications of the ACM</I>, 1983, Vol. 26, No. 11,
pp. 832--843; reprinted in: Peter G. Raeth, <I> Expert Systems: A
software methodology for modern applications</I>, IEEE Computer Society
Press, Los Alamitos, CA, 1990, pp. 248--259. 
<P>

A pioneer paper of Allen, in which he introduces different ordering
relations between intervals and explains how they can be used to
represent and process expert knowledge about the times of different events.