An entity is a physical or abstract object (for example, Mr. Douglas, the "Sales Information System" project) that can be distinguished from other objects and for which information is to be stored. Entities are divided into entity types according to their properties.

Each entity type is assigned attributes, which describe the entities of the entity type. The properties of entities are described by means of actual values for the attributes.

An attribute consists of a name and a definition of the possible values for the attribute (for example, the attribute color with the values white, black, yellow, and so on). One or more attributes are labeled as key attributes. The values of the key attributes uniquely identify an entity within its entity type.