EXPRESSING TIME INTERVALS AND REPETITION WITHIN A FORMALIZATION OF CALENDARS

We investigate a formal representation of time units, calendars, and t ime unit instances as restricted temporal entities for reasoning about repeated events. We generalize Alien's interval relations to a class level, and based on interval classes we define time units. We examine characteristics of time units, and provide a categorization of the hie rarchical relations among them. Hence we define an abstract hierarchic al unit structure (a calendar structure) that expresses specific relat ions and properties among the units that compose it. Specific objects in the time line are represented based on this formalism, including no nconvex intervals corresponding to repeated events. A goal of this res earch is to be able to represent and reason efficiently about repetiti on in time.