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<chapter id="calendar-architecture">
<title>Architecture of the Calendar</title>
<para>
This chapter gives an overview of the Evolution Calendar
architecture. It describes the model/view split of the calendar
into a personal calendar server, or PCS, and the GUI clients
that appear inside the Evolution shell.
</para>
<!-- Model/View Separation -->
<sect1 id="calendar-model-view">
<title>Model/View Separation</title>
<para>
Like other base components in Evolution, the calendar
separates the data model from the views or clients. This is
done so that multiple clients can access the same calendar
data in an orderly fashion and without clashes. For example,
the user may be running a graphical calendar client. If he
then wants to synchronize his calendar with a handheld device,
then the corresponding synchronization program (e.g. a conduit
for the <application>gnome-pilot</application> package) will
also need to access the calendar storage. It is important
that both the GUI client and the synchronization program keep
a consistent view of the calendar at all times, otherwise one
of them will be left in an inconsistent state if the
calendar's data changes unexpectedly.
</para>
<para>
Evolution puts the calendar storage in a daemon called the
Wombat and completely separates it from clients who wants to
access calendar data. This part of the Wombat is called the
personal calendar server, or &PCS;. Clients must contact the
&PCS; and ask it to open an existing calendar or create a new
one. When a calendar component object (e.g. an appointment or
to-do item) changes in the &PCS; it will notify all the
clients that are using the component's parent calendar.
</para>
</sect1>
<!-- Personal Calendar Server -->
<sect1>
<title>Personal Calendar Server</title>
<para>
The personal calendar server, or &PCS;, provides centralized
management and storage of a user's personal calendar.
Multiple clients can connect to the &PCS; simultaneously to
query and modify the user's calendar in a synchronized
fashion. The main features of the &PCS; are as follows:
</para>
<formalpara>
<title>Storage</title>
<para>
The &PCS; is responsible for loading and saving calendars.
Centralizing the loading and saving functionality allows
multiple clients to use the same calendar at the same time
without having to worry about each other.
</para>
</formalpara>
<formalpara>
<title>Basic Queries</title>
<para>
The &PCS; provides functions to do basic queries on a
calendar, for example, a client can ask the server for a
list of all the appointments in the calendar, or for all the
data for a specific appointment.
</para>
</formalpara>
<formalpara>
<title>Recurrence and Alarm Queries</title>
<para>
</para>
</formalpara>
</sect1>
</chapter>
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