Evolution Developer's Guide
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# How the Wombat generates alarm instances

This chapter describes the algorithm that the Wombat uses internally to generate instances of a calendar component's alarms. You do not need to read this chapter if you are simply using the client-side functions.

# What makes up an alarm trigger

VTODO and VEVENT calendar components can have any number of alarms defined for them. Each alarm has a trigger specification, an alarm type (display, audio, email, or procedure), and data corresponding to the alarm type. The Wombat side of things is interested only in the trigger specification, since this is all that the Wombat needs to produce alarm instances.

An alarm trigger can be relative or absolute. Relative triggers occur a certain time before or after the start or end of a calendar component's occurrence. For example, you could configure a trigger to notify you 15 minutes before an appointment starts, so that you can get to its location on time; or another one to notify you 5 minutes after another person's meeting has ended, so that you can call that person on the phone after the meeting and not disturb him while there. Absolute triggers occur at a specific point in time; you can configure an alarm to trigger exactly at a particular date and time that has no relation to the component's occurrences at all.

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Non-graphical Clients | Generating trigger instances