Can you explain the difference between a physical model and a logical model?

A logical model describes the structure of data independent of any specific technology. It focuses on entities, attributes, relationships, and constraints, often represented by an Entity-Relationship diagram. It answers "what" the data is and how it relates. A physical model, on the other hand, translates the logical design into a concrete implementation on a particular database system. It specifies tables, columns, data types, indexes, storage details, and performance tuning. The logical model is technology-agnostic, while the physical model is database-specific. For example, a logical model might define an "Employee" entity with attributes like name and salary, whereas the physical model would create an "employees" table with columns VARCHAR, DECIMAL, and appropriate indexes.