Library metadata will increasingly include (some or all of) the content of the resource cataloged to complement the descriptive data. It is currently hard for libraries to capture what is in a book (granted, we have subject headings, but they categorize resources using controlled rather than natural language), and as a consequence some books are prone to being easily overlooked.
A friend of mine is doing research on two hardly known female Austrian composers of the 1930s for her Master’s thesis. In one instance, she only found out that a book contained important biographical information about them through the book’s index on the publisher’s website listing their names (which she stumbled across via … Google). Obviously neither a table of contents nor a library record could have supplied this pointer. So, failing a full-text scan, digital versions of the parts of a book that serve as windows into the content are helpful additions to the metadata. This is not restricted to TOCs (which can already be found in a number of records), but includes indexes as well. Incidentally, it is not without a reason that the Topic Maps technology was originally developed for automated electronic indexes – they are gateways into a book’s contents, reflecting the main concepts it deals with. All of the above is assuming, of course, that an index exists – as Baron Campbell says in Lives of the Chief Justices:
“So essential do I consider an Index to be to every book, that I proposed to bring a Bill into Parliament to deprive an author who publishes a book without an index of the privilege of copyright; and, moreover, to subject him, for his offence, to a pecuniary penalty.”
(quoted from: Thomas B. Passin: Explorer’s Guide to the Semantic Web)
If publishers or other providers of bibliographic metadata are ready to make additional material about their publications available for display in library catalogs (so that efforts aren’t duplicated), if reviews, abstracts, indexes or TOCs are assembled in one central place, indexed and thus searchable, we stand a much better chance to help users discover the knowledge structure contained in books. Moreover, by not requiring them to go to the shelf to look inside the book or even request it from closed stacks, we get a step closer to fulfilling Ranganathan’s fourth law: Save the time of the reader.