Abstract: In an observable a slot is defined in which a "name", "data", and read/write procedures are stored that execute read and write operations with respect to those data. An observer acquires a slot descriptor by opening the slot with the "name" stored in it, then executes a read method or a write method with respect to it to call the read/write procedure and access the "data" stored in the slot. If the "data" in the slot are modified by the execution of the write procedure, the observable issues update events to all of the observers connected to it. When each observer receives that update event, the data modification is confirmed by execution of an isModified method.