What is the master key to recording?

A master key is understood as a field or a set of fields that uniquely (uniquely) identify a record. The master key should be as small as possible: it should not contain fields, the removal of which from the primary key will not affect its uniqueness.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.