Logical models show what a system is or does. They are implementation independent; that is they depict the system independent of any technical implementation. As such, logical models illustrate the essence of the system. Popular synonyms include essential model, conceptual model and business model.
Physical models: show not only what a system is or does, but also how the system is physically and technically implemented. They are implementation dependent because they reflect technology choices and the limitations of those technology choices. Synonyms include implementation model and technical model.
Due to the following reasons logical models are superior for structuring business requirement
• Logical models remove biases that are the result of the way the current system is implemented or the way any one person thinks the system might be implemented. Logical models encourage creativity.
• Logical models reduce the risk of missing business requirements because we are too preoccupied with technical details. Such error are almost always much more costly to correct after the system implementation. By separating what the system must do from how the system will do it, we can better analyze the requirements for completeness, accuracy and consistency.
• Logical models allow us to communicate with end users in nontechnical or less technical languages. Thus we don‘t lose ―business‖ requirements in the technical jargon of the computing discipline