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<!doctype article PUBLIC "-//Davenport//DTD DocBook V3.0//EN" [
<!entity Evolution "<application>Evolution</application>">
<!entity CUA "<acronym>CUA</acronym>">
<!entity PCS "<acronym>PCS</acronym>">
]>
<article class="whitepaper" id="calendar">
<artheader>
<title>&Evolution; Calendaring Framework</title>
<authorgroup>
<author>
<firstname>Federico</firstname>
<surname>Mena Quintero</surname>
<affiliation>
<address>
<email>federico@helixcode.com</email>
</address>
</affiliation>
</author>
</authorgroup>
<copyright>
<year>2000</year>
<holder>Helix Code, Inc.</holder>
</copyright>
<abstract>
<para>
The &Evolution; groupware suite provides a framework for
developing calendaring applications, as well as a graphical
calendar client and a personal calendar server. This white
paper describes the architecture of the &Evolution;
calendaring framework.
</para>
</abstract>
</artheader>
<!-- Introduction -->
<sect1 id="introduction">
<title>Introduction</title>
<para>
Calendaring is an important part of a groupware suite. A
calendaring framework will allow a user to keep a personal
calendar and have several applications use it. Such
applications could be a graphical calendar client that the user
employs to schedule appointments and keep track of his time, a
<productname>Palm Pilot</productname> synchronization client, or
a simple alarm or reminder utility. A comprehensive calendaring
framework will also allow multiple users to schedule
appointments between each other; for example, a project director
may want to schedule a weekly meeting with the rest of the
project members, or a person who owns a large house may want to
schedule a big party with his friends. The attendees will then
want to reply with messages such as, “I will
attend”, or “I will attend only if the proposed time
is changed”.
</para>
<para>
The &Evolution; groupware suite provides a framework for
developing calendaring applications, as well as a graphical
calendar client or calendar user agent (&CUA;) and a personal
calendar server (&PCS;).
</para>
<para>
The following sections explain the basic calendaring framework,
the functions of the calendar user agent and the personal
calendar server, and the relationship between the two.
</para>
</sect1>
<!-- Personal Calendar Server -->
<sect1 id="pcs">
<title>Personal Calendar Server</title>
<para>
The personal calendar server (&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>
Clients can ask the &PCS; for a list of the appointments that
occur within a specified time range; for example a graphical
client that has a per-week view could ask the &PCS; for all
the appointments that occur in a particular week. This
includes multiple occurrences of a single recurring event; for
example, the object for “a 1-hour meeting that occurs on
every Tuesday and Thursday” is represented inside the
&PCS; as a single event with a recurrence rule. Similarly,
clients can ask the &PCS; for a list of events that have
alarms that trigger within a specified time range.
</para>
</formalpara>
<formalpara>
<title>Notification of Changes</title>
<para>
This is the most important function of the &PCS;, as it allows
multiple calendar clients to maintain a unified view of the
calendar between the server and themselves. When a client
asks the &PCS; to modify or remove an event, the &PCS;
notifies all the clients that are connected to it about the
change. The policy is that “the server is always
right”; clients can act as dumb views onto the
calendar's data and they will be notified by the &PCS; when
something changes.
</para>
</formalpara>
</sect1>
</article>
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