Chapter 3 Building Physical Diagrams
A reference is a link between a parent table and a child table. It defines a referential integrity constraint between column pairs for a primary key, or alternate key, and a foreign key, or between user specified columns in both tables.
When column pairs are linked by a reference, each value in the child table column refers to an equivalent value in the parent table column.
Within a reference, each column pair is linked by a join. Depending on the number of columns in the primary key, or alternate key, or the number of specified columns, a reference can contain one or more joins.
A reference normally links primary key, or alternate key, columns to foreign key columns.
The two tables SALE and STORE are linked by a reference. STORE is the parent table and SALE is the child table. The reference contains a join which links the primary key column STORE ID (the referenced column) to the foreign key column STORE ID (the referencing column).
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