A method of updating a user session with external data received from external systems (5, 5'), characterized in that it comprises the following steps performed with at least one data processor: - receiving, at a synchronizer in communication with the user session and a data store, a request from the user session to retrieve a stored user dossier from the data store, wherein a dossier is a set of data; - retrieving, at the synchronizer, the stored user dossier from the data store, creating, at the synchronizer, from the stored user dossier an intermediate dossier comprising at least the content of the stored user dossier and delivering the intermediate dossier to the user session, as a session dossier, for operations by a user; - storing temporarily, in an event queue in communication with the synchronizer, external data received and/or updating, at the data store, the stored user dossier with external data received; - receiving, at the synchronizer, a user update performed on the session dossier, updating the session dossier with the received user update and returning the updated session dossier to the user session; - upon receiving, at the synchronizer, a request for refresh sent by the user session: - retrieving, at the synchronizer, the updated stored user dossier, - retrieving, at the synchronizer, all events in the event queue, - merging, at the synchronizer, the retrieved updated stored user dossier with updates from all the events retrieved from the event queue and saving the merged dossier to the data store, and - merging, at the synchronizer, the merged dossier with the updated session dossier and returning the result to the user session; and - upon receiving, at the user session, an instruction to close the user session, asking a question to the user through a user interface of the user session about saving or not saving the session dossier: - upon receiving an instruction from the user for saving the session dossier, updating the session dossier through merging received external data, the stored dossier and the session dossier, and saving it in the data store; and - upon not receiving an instruction for saving the session dossier or upon receiving an instruction to delete the session dossier, not saving the session dossier and not updating the stored dossier in the data store. - receiving, at a synchronizer in communication with the user session and a data store, a request from the user session to retrieve a stored user dossier from the data store, wherein a dossier is a set of data; - retrieving, at the synchronizer, the stored user dossier from the data store, creating, at the synchronizer, from the stored user dossier an intermediate dossier comprising at least the content of the stored user dossier and delivering the intermediate dossier to the user session, as a session dossier, for operations by a user; - storing temporarily, in an event queue in communication with the synchronizer, external data received and/or updating, at the data store, the stored user dossier with external data received; - receiving, at the synchronizer, a user update performed on the session dossier, updating the session dossier with the received user update and returning the updated session dossier to the user session; - upon receiving, at the synchronizer, a request for refresh sent by the user session: - retrieving, at the synchronizer, the updated stored user dossier, - retrieving, at the synchronizer, all events in the event queue, - merging, at the synchronizer, the retrieved updated stored user dossier with updates from all the events retrieved from the event queue and saving the merged dossier to the data store, and - merging, at the synchronizer, the merged dossier with the updated session dossier and returning the result to the user session; and - retrieving, at the synchronizer, the updated stored user dossier, - retrieving, at the synchronizer, all events in the event queue, - merging, at the synchronizer, the retrieved updated stored user dossier with updates from all the events retrieved from the event queue and saving the merged dossier to the data store, and - merging, at the synchronizer, the merged dossier with the updated session dossier and returning the result to the user session; and - upon receiving, at the user session, an instruction to close the user session, asking a question to the user through a user interface of the user session about saving or not saving the session dossier: - upon receiving an instruction from the user for saving the session dossier, updating the session dossier through merging received external data, the stored dossier and the session dossier, and saving it in the data store; and - upon not receiving an instruction for saving the session dossier or upon receiving an instruction to delete the session dossier, not saving the session dossier and not updating the stored dossier in the data store. - upon receiving an instruction from the user for saving the session dossier, updating the session dossier through merging received external data, the stored dossier and the session dossier, and saving it in the data store; and - upon not receiving an instruction for saving the session dossier or upon receiving an instruction to delete the session dossier, not saving the session dossier and not updating the stored dossier in the data store.