Identifying and Non Identifying relationships

Relationships between two entities may be classified as being either "identifying" or "non-identifying". Identifying relationships exist when the primary key of the parent entity is included in the primary key of the child entity. On the other hand, a non-identifying relationship exists when the primary key of the parent entity is included in the child entity but not as part of the child entity's primary key. In addition, non-identifying relationships may be further classified as being either "mandatory" or "non-mandatory". A mandatory non-identifying relationship exists when the value in the child table cannot be null. On the other hand, a non-mandatory non-identifying relationship exists when the value in the child table can be null.
Here's a simple example of an identifying relationship:
Parent
------
ID (PK)
Name

Child
-----
ID (PK)
ParentID (PK, FK to Parent.ID) -- notice PK
Name
Here's a corresponding non-identifying relationship:
Parent
------
ID (PK)
Name

Child
-----
ID (PK)
ParentID (FK to Parent.ID) -- notice no PK
Name