Method and apparatus for representing recurring events

Abstract

A method and apparatus for representing and storing the schedules of recurring events. The schedules are represented by recurrence rules generated according to a specific grammar. According to the grammar, each recurrence rule is composed of one or more recurrence commands. Each recurrence command corresponds to a cycle and includes a time interval indicator that specifies the duration of the cycle and a repeat quantity that determines the number of times the cycle is repeated in the schedule. Each recurrence command may also include an occurrence list that specifies at what times during a particular cycle the event occurs. The occurrence list may specify times in absolute or relative terms. Thus, the grammar supports recurrence rules for representing the schedule 'first and tenth of every month' as well as the schedule 'second Thursday and last Friday of every month'. To represent schedules that terminate before the last event in the last cycle is completed, a symbol may be inserted into the occurrence list to distinguish the events that are performed on the last cycle from the events that are not performed on the last cycle. Complex schedules that involve cycles repeated within cycles are represented by multiple-command recurrence rules. The stored recurrence rules may be parsed to determine when events will occur. The grammar may be applied to a variety of applications, including calendar programs, video cassette recorders and home automation devices.