What is a Key Matrix?

In The Matrix (movie), how does the system architecture of the matrix decide what human will lead what kind of life in the matrix?

• If we say every human is a "process" inside a matrix, then how does the system allocates a process it's attributes (professions, family, lifestyle etc.). Is it done randomly or through some algorithm? Has any reference been made in the movie about it ?

• Answer:

  I guess not,it wasnt mentioned anywhere. But then again we can deduce it how it was managed, since everything was based on choice algorithm, so it must be as per the individuals choices as in real life. As in real life people make bad choices and thus repent it, like Neo repented his current life in the matrix.