Federico Mena Quintero

federico@helixcode.com

2000 Helix Code, Inc. 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. 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 Palm Pilot 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”. 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;). 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. 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: 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. 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. 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. 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.