Diana Cukierman, James Delgrande
We are investigating a formal representation of time units and calendars, as restricted temporal entities for reasoning about activities. We examine characteristics of time units, and provide a categorization of the hierarchical relations among them. Hence we define an abstract hierarchical unit structure (a calendar structure) that expresses specific relations and properties among the units that compose it. Calendar structures subsume systems that can be based on discrete units together with a repetitive containment relation.