ER diagram for inventory management system depicts the key concepts and relationships required for inventory resource management. It is not a complete data model showing every necessary relational database table, nor is it intended to be a prescriptive design for resource management system implementations. Entity keys are used to identify instances of entities in a unique way. Candidate keys are attributes with unique values, and one of them is designated as the primary key. The attribute domains should be pre-defined. The entities in an ER diagram for inventory management system are the Fundamental entity, Subordinate entity, Associative entity, Generalisation entity, and Aggregation entity.