A use-case is specified as a set of possible scenarios of interactions. Scenarios can be decomposed into workflows on different granularity levels. Use-cases are fundamentally a text-based documentation form written in natural language text. The textual description of a complicated scenario can be ambiguous, incomplete and inconsistent. In this paper we demonstrate a conceptual modeling method for representing use-case descriptions by using a graphical language. Simple interaction loops are viewed as fundamental elements for composition of scenarios. Each interaction loop is analyzed separately and therefore it provides a natural way of decomposition. Modeling of overlaying interaction flows between organizational and technical components enables separation of crosscutting concerns in system engineering without requirement to specify a complete solution. The goal of this paper is to demonstrate the advantages of conceptual modeling approach, which allows to introduce evolutionary extensions and to construct use-case scenarios with a comprehensible structure.