I want to devekop chapter 13 further, and I need clue/help/advise from the authors of this great book.

Question : How to create categorical articles?

The sample code in the book just show how to create general article. In the real world website, the articles always belong to category/section.

How can I start doing the process?

Great book, but very appaling support - I notice a lot of post have 0 repplies (include my post). So watchout for newbie who bought the book looking for help.