This invention relates to a communication system between a programmable logic controller (PLC) equipped with an HTTP server and a client machine (C) via a network (B), characterized in that it comprises, in the central processing unit (CPU) of this controller, a means (API 1a) for adding “group sheets” (M1, M2. . . ) in XML format, whereon elements or signals for watching or controlling the process automated by the application of the programmable logic controller are grouped, as well as a means (API 1b) for adding/deleting elements or signals on these sheets, by specifying the type thereof, a means (API 1c, API 1d) for reading or writing these elements, and a means (API 2b, API 2c, API 2d) for reading these sheets and for writing on these sheets upon a query from the HTTP server.