| Abstract
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In this paper we present a reusable time o … In this paper we present a reusable time ontology for large-scale knowledge system applications, that is intuitive, expressive, formally defined, logically consistent, and ready-to-use. Our underlying time theory treats both time points and time intervals as primitive elements on a time line, and the ontology contains a class hierarchy, relations, axioms and instances built on those primitives. The main contributions of this work are the following three. (1) The ontology makes a distinction between closed and open intervals, as opposed to many previous time ontologies. However we provide flexibility of usage by providing two sets of relations on intervals: one that assumes that distinction and one that does not. (2) Time granularity is implemented in the ontology to facilitate representing time in varying granularity in a layered model and switching from or relating one granularity to a coarser/finer one. (3) The ontology includes classes for calendar months, calendar days and weekdays. The instances of these classes have many attributes associated with them that are useful in knowledge domains concerning human activities. We also present examples of usage of the ontology and comparisons with previous time ontologies. comparisons with previous time ontologies.
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