The paper describes the stages of the general structure modeling process, using an object-oriented paradigm. The first part describes basic ideas about the structure modeling and implementation of the simulation mechanism in Cosmos tool. The tool was developed primarily as the basis for handling of network components and network, but is easily applied to any system type. Examples of the addition of new features to base classes, e.g. analytic and optimization procedures, and availability model are presented. The last part explains the use of developed components for IP over WDM network modeling, which had been the prime issue that initiated development of the described models.