A common way to express incomplete qualitative knowledge about an order of occurring events is Allen’s interval algebra A [1]. Unfortunately, the main reasoning tasks of A, consistency checking ISAT and strongest implied relation computation ISI, are intractable [10]. To overcome this, some tractable subclasses of A have been identified, e.g., the continuous algebra C [9], the pointisable algebra P [7], and the ORD-Horn algebra H [8]. These subalgebras form a strict hierarchy with H as the largest tractable subalgebra that contains all thirteen basic relations [8]. To solve ISAT(H) and ISI(H), several approaches like constraint propagation [8], linear programming [3], or graph oriented approaches [2] have been presented.