The guideline of this introduction to computer science is the question of which approaches give a problem its computational contour and what techniques are available to analyze or design information systems. Models arise from the synthesis of different perspectives of a system, which are described through concise diagrams: entity-relationship, system structure, state transition, and sequence diagrams. An inherent component of these graphical description techniques is the characterization of the underlying data, for example in functional programming. The authors use AutoFOCUS in their work for diagram-oriented system design, consistency checking, and simulation. They explore how diagrams can be translated into formal specifications and where a system development derives its arguments.