Weak Entity Types
CSCI 6442




Most entity types are strong entity types, that exist
independently from other entity types
A strong entity type always has a unique identifier that
distinguishes each occurrence of that entity type
A weak entity type needs another entity type for its
identifier
The entity type on which the weak entity type depends is
called the identifying owner
Example
Employeeee
belongs
Dependent


The identifying relationship is the relationship between a
weak entity type and its owner
The weak entity identifier is its partial identifier combined
with that of its owner.
Types of Weak Entities



Existence-dependent entities—existence depends on
existence of another (strong) entity
Associative entities—a many-many relationship
Subtype entities—entity type that inherits its identity
from a supertype
Example
Student
registers
Party
Employee
Company
Course