Abstract: Calendar appointments are indexed using a modified relational interval tree which identifies a fork node for each appointment, and indexes the appointment based on the identified fork node. When a query interval is received, a fork node is identified for the query interval and the index is searched using the fork node identified for the query interval. Intersecting appointments are identified as those appointments that an interval that includes the fork node for the query interval, and those appointments that have a fork node on a path traced through the modified RI tree to obtain the fork node for the query interval, and that overlap with the query interval.