Entity types

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.

Entities, entity types, attributes

Term

Example

Entities

Mr Douglas

Ms Roberts

Ms Stone

'Sales Information System' project

'Warehouse Management' project

Entity types

employee
project

Attributes

Attributes of entity type ‘employee’:

personnel number (key attribute)

name

address

date joined company

Attributes of entity type ‘project’:

project number(key attribute)

name

start date

end date

project manager

Other subjects:

Data Modeler: overview

Attributes of entity types

Relationships

Specializations/generalizations

Structural concept: data model and data model hierarchy

Top-down and bottom-up modeling

Consistency checks