The transformation of keys which are supposed to be used as primary key into generic key by the system is called as key restructuring.
The problem is something like this, let us a say there was an existing system
for keeping record of each house in a town. The uniqueness of the house was
represented by a 4 character word where first two characters give the house
number and the last two characters represent the street name.
Then the town expanded into a big city and correspondingly the house number
changed. Now the first two digits of the same house changed in the unique key.
To avoid such changes and have a generic key for uniqueness, key restructuring
is done by the system.
