Different languages, tools, and techniques are used for the development of software systems, including database and knowledge-based systems. Although underlying languages employ structuring concepts such as classification, modularization, generalization, and perspectives, these common concepts remain overshadowed by differing terminologies and notations, due to the separate histories of software engineering, databases, and knowledge representation. Currently the still more complex and ambitious requirements on software systems call for integrated solutions concerning software engineering environments. As a starting point toward integration, in this paper we aim at deriving a common structural level for software systems. To approach this goal we start by analyzing the human thought process on one hand and successfully applied structuring techniques on the other hand to derive a catalogue of 10 structuring concepts. Building on that, a self-contained language called SFW (structuring framework) is introduced to provide means for a general and uniform specification of the structure of software systems. SFW is aimed at providing a catalogue of reference for structuring concepts in today's languages as well as a suggestion to establish a uniform structural level in future approaches.