Use of Content
An entity relationship diagram forces questions about ownership and existence. It is not possible to draw a foreign key relationship without deciding who holds the reference and what happens when the referenced record is removed. These are not technical questions. They are business questions with technical consequences.
A sequence diagram forces questions about time and trust. When component A calls component B, what does A assume about B's response time? What does A do if B fails? What is the contract between them, and who defined it? A sequence diagram makes these assumptions visible because it requires them to be drawn.
A state diagram forces questions about completeness. Every state a record can be in must be named. Every transition between states must have a trigger. The exercise of drawing a state diagram almost always reveals states that were assumed but never named, and transitions that were expected but never designed for.
The common assumption is that a system designer sits down, understands the requirements, and produces a diagram that represents the system. In practice, the diagram is the process by which the system becomes understood. It does not follow clarity. It produces it.
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Diagrams produced under time pressure, after the system design is considered complete, or by someone working alone without challenge, carry a higher risk of encoding assumptions rather than testing them. The format is correct. The thinking behind it may not be.
A UML diagram is only as reliable as the process that produced it.
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An entity relationship diagram forces questions about ownership and existence. It is not possible to draw a foreign key relationship without deciding who holds the reference and what happens when the referenced record is removed. These are not technical questions. They are business questions with technical consequences.
A sequence diagram forces questions about time and trust. When component A calls component B, what does A assume about B's response time? What does A do if B fails? What is the contract between them, and who defined it? A sequence diagram makes these assumptions visible because it requires them to be drawn.
A state diagram forces questions about completeness. Every state a record can be in must be named. Every transition between states must have a trigger. The exercise of drawing a state diagram almost always reveals states that were assumed but never named, and transitions that were expected but never designed for.