Hi @P_M_Lucaci
The 6th heading Basic System Design and Algorithm explains two different ways that how to generate a short and unique key for a given URL.
In 6b: Generating keys offline only describes one of the ways that generates random six-letter strings beforehand and stores them in a database (let’s call it key-DB). Whenever we want to shorten a URL, we will take one of the already-generated keys and use it. This approach will make things quite simple and fast. Not only are we not encoding the URL, but we won’t have to worry about duplications or collisions. KGS will make sure all the keys inserted into key-DB are unique.
So, don’t compare it with others, every approach has a different significance, pros, and cons. Some of them use full URLs with their respective hashes, some deal with keys only, and some have PK URL hash.
Hope it will help, Thank you