concepts of information system

1 A Natural Structuring ConceptInformations systems are being designed as parts of increasingly complex systems. The complexity of these systems may result from their size, from the complexity of the information they need or generate, from the complexity of their behavior, from a long evolution,... In order to deal with this complexity, adequate structuring mechanisms are needed. We argue that the concept of agent is appropriate and natural to deal with the complexity of studied systems by decomposing them in a natural way.
When doing Requirements Engineering for an IS, it is important to model not only the ``to-be IS'' (what Jackson calls the machine [8]) but also the environment with which the machine will interact, which exists in spite of the machine (thereby constraining the machine) and in terms of which the requirements have to be expressed. Such an environment description can be structured in a natural way by identifying various agents having interactions among themselves and with the machine. The environment can be considered as a composite system [2] made of agents of different kinds like human beings (probably users of the IS), existing software, computer hardware or other kinds of devices like mechanical devices. All these agents have characteristics and behaviours that need to be taken into account to correctly model the behaviour of the ``to-be IS''.
The concept of agent is therefore a natural basic building block for structuring the description of an IS and its environment. Beneficial consequences of this structuring appear at various stages of the Requirements Engineering process. When modelling, it is well known that structuring allows analysts, amongst other things, to focus on some specific concerns and to distribute the work among them. Similarly, such advantages appear at the validation stage where a cooperative animation technique allows different people to play the role of agents and test requirements descriptions against scenarios (see [7]). Compositional reasoning can also be applied on a specification structured with agents, allowing to reason on or prove properties of some agents, by relying on conclusions previously achieved for other agents (see [11]).