Which process model notation is primarily used for describing information systems requirements?

The correct answer is UML (Unified Modeling Language), which is predominantly utilized for describing information systems requirements. UML provides a standardized way to visualize the design of a system. It includes a variety of diagrams that can represent different aspects of a system, such as structure (class diagrams), behavior (use case and activity diagrams), and interactions (sequence diagrams). This versatility makes UML an essential tool for software development and systems engineering, as it allows stakeholders to communicate their requirements clearly and effectively.

While other notations exist, such as BPMN (Business Process Model and Notation), which focuses more on business process modeling, UML's primary strength is in capturing detailed technical and functional requirements of information systems. This makes it more suitable for technical contexts than some of the other options, which serve different purposes within their respective fields. For instance, IDEF is primarily used for functional modeling and analysis, while VSM (Value Stream Mapping) focuses on lean processes and waste identification rather than technical system requirements.