Quality operating of information systems and service level agreement

ISO 9126 defines the quality of software features and sub features, and presents itself as a model of international consensus. There are two features of computer applications in operations that deserve our attention: the availability and the response time. In our research, we limit ourselves to the unavailability. The purpose of this paper is to show that, to better manage the unavailability of an Information System, one must implement a Service Level Agreement (SLA) with a good system of measurement of Performance Indicators. A good definition of performance indicators is needed and a good method of measurement also. The control of unavailability depends on the method used for statistical process. It seems to be the cheaper and easiest way to stabilize the system and to obtain a lasting satisfaction of the end customer.