A trivial web search with the author name and the book header should usually return Amazon and similar sites the book could be purchased, as well as probably some alternative sites, and the authors website as well. Same about ISBN number.

Hence, I think, URLs are redundant. Also, it is not uncommon for them to "rot" (disappear or change over time).

A trivial web search with the author name and the book header should usually return Amazon and similar sites where the book could be purchased, as well as probably some alternative sites, and the authors website as well. Same about ISBN number.

Hence, I think, URLs are redundant. Also, it is not uncommon for them to "rot" (disappear or change over time).