The following info is from Chapter 2 of Database Systems by Carlos Coronel
1Basic Building Blocks
Entity: A person, place, thing, concept or event for which data can be stored.
Attribute: A characteristic of an entity or object.
Relationship: An association between entities.
One-to-many (1:M or 1..*) relationship: Associations among two or more entities that are used by data models.
In a 1:M relationship, one entity instance is associated with many instances of the related entity.
A painter creates many different paintings, but each is painted by only one painter.
“PAINTER paints PAINTING”
Many-to-many (M:N or *..*) relationship: Association among two or more entities in which one occurrence of an entity is associated with many occurrences of a related entity and one occurrence of the related entity is associated with many occurrences of the first entity.
An employee may learn many job skills, and each job skill may be learned by many employees.
“EMPLOYEE learns SKILL”
One-to-one (1:1 1..1) relationship: Associations among two or more entities that are used by data models.
“EMPLOYEE manages STORE”
Constraint: A restriction placed on data.
Business rule: A description of a policy, procedure, or principle within an organization.