Some people wonder why, with full-text search available, an ebook might still need an index. If you happen to be one of them, go read “Missing Entry: Whither the eBook Index?” ;). This article is a great summary of the value of indexes (even or especially for books in electronic form) and gives examples (with nice illustrations!) of what enhanced indexes might look like. Indexes with enhanced functionality can be much more interactive and appealing to the user than pure lists of words with a page indication.
Just like subject cataloging, indexes offer a value that cannot be replaced by full-text search. They chart a structured map of the content, show paths into the information, expose relationships and go beyond pure search (which just pulls up instances of terms) in that content is analyzed and arranged meaningfully.
Experienced indexer Jan Wright points out in a fascinating podcast on ebook indexing that an index is a discovery feature just like other metadata. She says: “The more tools for getting into information readers are given, the happier they will be.”
The potential of what ebooks can be (beyond static representations of regular print books) has not been tapped yet – indexes are only one example. We’ll just have to wait for EPUB to recognize its importance and address it explicitly in its specification, and for publishers to incorporate smarter indexes into their products.