The core of Yourdon-DeMarco notation lies in its use of DFDs to represent the flow of data within a system. A DFD consists of four types of elements: processes, data stores, data flows, and external entities. Processes transform data from input flows into output flows. Data stores hold data that is used by processes. Data flows represent the movement of data between processes, data stores, and external entities. External entities are sources or destinations of data that interact with the system.
Yourdon-DeMarco notation emphasizes the decomposition of systems into smaller, more manageable components. This is achieved through the use of hierarchical DFDs, where a high-level DFD can be broken down into more detailed DFDs. This hierarchical approach allows for a clear and structured representation of system functionality.
The notation also includes a set of rules and guidelines for creating and interpreting DFDs. These rules ensure that the diagrams are consistent, unambiguous, and easy to understand. For example, processes should have a single, well-defined function, and data flows should represent the movement of data rather than control information.
Yourdon-DeMarco notation is valued for its simplicity and clarity, making it accessible to both technical and non-technical stakeholders. It provides a visual representation of system functionality, which can be used to communicate requirements, design decisions, and system behavior. However, it is important to note that the notation is not without its limitations. It may not be suitable for modeling complex control flows or real-time systems, and it does not provide a formal method for verifying system correctness.