The key must be such that it uniquely identifies a record.
Each year has had a different set of two colors to uniquely identify its participants.
On many systems both most be specified to uniquely identify the security.
Any activity is uniquely identified by the name of the stage and the column number.
Currently, there are four series running, each uniquely identified with colors.
What it does allow, though, is for that hardware to be uniquely identified.
Each medical student is uniquely identified with the year and a roll number in the batch.
Dimension table rows are uniquely identified by a single key field.
It may be used to create an identity column which uniquely identifies each record in a table.
This place is often used in legal documents, together with name and date of birth, to uniquely identify a person.