Maxwell, when I first learned about drawing analysis models, I kept searching for the one picture that would tell me everything I needed to know about the system. As you observe, there is none. Different types of products demand different types of models, such as event-driven versus data-flow or process driven. Sometimes you want a detailed, multi-level data flow diagram; other times you just need a high-level cut at it. The astute BA needs to select an appropriate set of diagrams to meet their communication and analysis needs.