1. A look at the data modeling process
: Conceptual → Logical → Physical → ERD → DBMS (schema work)
2. A look at keys in the relational data model
(around textbook p.31)
Candidate key
Each column / attribute in a relation / table / entity
Any of which can potentially become a primary key, alternate key, composite key, or foreign key.
Primary key
Among the attributes/columns that make up a relation/table/entity,
one that is not null (always present) and has no duplicates,
used to uniquely identify each tuple within the relation/table/entity.
Alternate key
The candidate keys other than the primary key.
Composite key
When no single attribute/column can serve as a primary key, two attributes are combined into a candidate key.
Foreign key
A key that maintains a relationship between two tables / entities.
The relationship carries business meaning.
The child table's FK references the parent table's PK.
The parent table's PK propagates into the child table as an FK.
