Free Databases
there are millions on the web
One way to search for a book in a library is to go to that library's web site and use the book catalog's search feature.
The information stored in the library's book catalog (a database) is free, but the search engine cannot go deep enough to crawl it.
The book catalog is part of the free deep web: it's out there for anyone to look at. You can get to it, but search engines can't.