A critical problem for practical KR is dealing with relationships that change over time. This problem is compounded by representation languages such as OWL that are biased towards binary relations; even when the relationships that vary with time are binary, the time the relationship holds typically requires a third argument. We discuss the standard approach to this problem, and contrast it to a new alternative based on a four-dimensionalist (perdurantist) ontology, which allows us to use more of the expressive power of description logics. The technique is usable in other logics as well.
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