Possibly the most interesting part of this section is the latter half which deals with Homomorphisms.
Theorem 6.12: First Isomorphism Theorem
Let be a surjective isomorphism of rings with kernel K. Then the quotient ring R/K is isomorphic to S.
If I understand this correctly then when comparing this to data transfer f represents the transfer of data from R to S where K is the amount of lost data. Looking at the kernel in Example 4 () we can say that of the data is lost during the transfer.