A method of sharing a group of one or more objects between a plurality of users, in which one or more of said plurality of users is able to change parameter data of at least one said object. The method comprises storing at least one version of each said object; when an object is changed, creating a new version of the object, the new version of the object comprising additional data relating to the creation of the new version; storing the new version of the object together with any version of that object before the change; providing all versions of the object to each of said plurality of users; and using the additional data provided for each version of the object to determine how to display the object. The group may be a calendar and each object may be an event in the calendar. In that case, the object parameter data may comprise a start time of the event, an end time of the event, a description of the event, a status of the event, whether the event is to be repeated and the persons attending the event. The additional data may comprise an identification of the user who made the change, a time at which the change was made, a description of the change, a user comment relating to the change and an identification of the previous version of the event from which the present version was created.