At the time that Guy wrote Database 101, he was helping a company that sold a contact-management application.
He wrote this book for computer novices to help them understand how a database works and what can be done with one.
This was back in 1991, so many things about databases have changed, but many basic principles have also remained the same.
Here’s where you can buy Database 101:
Guy has made Database 101 free in a PDF format: