SIP is also used more generally to refer to a search string likely to generate meaningful results from a search engine; that is, a string whose chance of occurring in a desirable result is much greater than its chance of occurring in a non-desirable result.
The big brown fox jumps over the lazy dog. The lazy dog did not like the fact that the big brown fox jumped over him, so the lazy dog ran after him.
You never have to log in to read Wikipedia. You do not have to log in even to edit articles on Wikipedia—anyone can edit almost any article, even without logging in. Nevertheless, creating an account is quick, free and non-intrusive, and it's generally considered a good idea to do so, for a variety of reasons.
''If you create an account, you can pick a username. Edits you make while logged in will be assigned to that name. That means you get full credit for your contributions in the page history (when not logged in, the edits are just assigned to your (potentially random) IP address). You can also view all your contributions by clicking the "My contributions" link, which is only visible when you are logged in.SIPs
For Book 1, the SIP would most likely be "Big Brown Fox" and "Lazy Dog"
For Book 2, the SIP would most likely be "Wikipedia", but not "account" because it is featured in Book 3 many times.
For Book 3, the SIP would most likely be "Contributions", and "Logged In"