Entity Relationship Diagrams

Question 1

ENTITY TYPE

what is a strong entity

Answer 1

a strong entity is one whose existence does not depend on the existence of any other entity in the same database. The primary key of a strong entity uniquely identifies each occurrence within the entity.

Question 2

ENTITY TYPE

what is a weak entity

Answer 2

a weak entity is one that depends on one or more strong entities for its existence. For this reason, strong entities are sometimes referred to as owner entities. A weak entity cannot be used independently because its existence depends on one or more owner entities.

Question 3

RELATIONSHIP PARTICIPATION

what is mandatory participation

Answer 3

mandatory participation describes a relationship where at least one occurrence of an entity must exist before any occurrences can be added to its associated entity. The mandatory side of any relationship is indicated by using a vertical line

Question 4

RELATIONSHIP PARTICIPATION

what is optional participation

Answer 4

optional participation describes a relationship between two entities where it is possible to add occurrences of one entity without the need to have existing occurrences in the associated entity. The optional side of a relationship is indicated by using a bold circle