You've been asked to help put together the back-end software for DeNile, a new online bookseller.

While the overall functionality of the website will be extensive, your job is to recommend how to structure the data for two tasks - retrieving a book by its ISBN number, and retrieving all of the books by a particular author (sorted by title.)  The author names will be last name first with no duplicate author names (assume an alternate universe.)

Given your knowledge of books, and more importantly...data structures, what sort of data structures/state would you for each of these tasks?  Give the specific implementation details of each structure using the proper terms.  Also describe how the author's books will be sorted.

You can assume that there is a process in place to distinguish between authors with the same name to keep names unique

Explain what you'd do and why, but code is neither required nor desired.