Nowadays the complexity and size of business systems is growing steadily and, as practise shows, the situation is not going to change in the nearest future. This necessitates difficulties not only for lifecycle of programmes’ development but for maintenance and expansibility also. That’s why, solving them, requires a broader perspective that views the system as consisting of other systems. This work looks what kind of methods can be applied in this context. The analysis of modern technologies (Java programming language) and modelling methods (functional decomposition and object-oriented system engineering) are presented. Suggested system decomposition approach is the synthesis of already existing ones. In this work new method has been applied for the development of experimental Information System of Territorial Departments of Environmental Inspection. The prototype of the mentioned system has been realized by using J2EE (Java 2, Enterprise Edition) technologies. Developed software implements the requirements for usage and maintenance (large number of the users, security rights, compatibility, centralised administration, etc.) of large distributed systems. Suggested approach may be used while expanding the existing software or developing similar applications.