I would write the thing you’re trying to do as:
map.short_book_page “:book_id/:page_id”, :controller => “books”, :action => “my_action”
Defining your route in this way will have the probably unintended effect of shortcircuiting your default routes (i.e. “:controller/:action”). If that doesn’t matter to you, then stick with the simplest option. But you can also put a condition on the parameters like this:
map.short_book_page “:book_id/:page_id”, :controller => “books”, :action => “my_action”, :book_id => /\d+/, :page_id => /\d+/
This should now only match in situations where you’ve got numeric parameters passed for both book_id and page_id.
You should understand that by doing it this way you’re draining your URLs of any semantic meaning and search engines will probably not know what to make of them. Best practice is generally to provide as many hints in your anchors as to what’s being linked to, if not in the link text itself then at least in the URLs. So unless you’re building an API and you don’t care about Google juice, I’d stick with the more traditional way of doing things.