Databases Reference
In-Depth Information
fIGure 11.2
Simple Instance Key.
Key and the Instance Key can exist side by side without any interruption
in both keys serving their individual respective purposes.
A Compound Instance Key, illustrated in Figure 11.3, uses a compound
key to uniquely identify each individual row of a table. That compound
key is made of the Entity Key, which is the key already assigned to an
entity, and a sequential numeric Instance Key. A Compound Instance Key
resets back to the value 1 for each entity within a table. The first Instance
Key value for each and every individual entity is the number 1. The last
Instance Key value for each and every individual entity is the number
of rows assigned to each individual entity. For example, if the entity A
has thirty-two rows, the Instance Key value for the first row is 1 and the
