An entity is a person, place, object, event, or concept about which the organization wishes to retain data. Entity instances are a single occurrence of an entity class. Employee Entity type is employee. Attributes Attributes are properties or characteristics of an entity or relationship. Name Address Phone Department Employee Name, address, etc. are attributes of the entity employee.
Simple attributes are atomic.
Single-valued attributes have one value. Multi-valued attributes have many potential values. Derived attribute is one that can be determined by stored data. Each instance must be uniquely identifiable. One or more attributes form a key that is unique.