Let's start by considering some of the bookbiz database entities. If we ignore for the moment most of the financial information that bookbiz tracks, a preliminary list of entities might look like this:
The authors who have written books published by the company
The books themselves
The editors working for the company
The subsidiary publishing houses owned by the company
Each item in this list is an entity with an independent existence in the world under consideration, that is, the world of the bookbiz database. Each is represented in the database by a table. (Other kinds of data elements are also represented by tables, but that's jumping ahead.)
The entities have certain properties that are to be recorded ...