Indexing for ebooks means creating a traditional back-of-the-book-style index familiar to all readers, where locators (traditionally page numbers), are hyperlinked to their referenced passages within the ebook.
When ebooks and their associated e-reader software were first developed, little attention was paid to the index. The index pages that were created for the print version of a book could be included in the ebook, but they were not hyperlinked, and their referenced pages numbers became useless in the ebook. Publishers often assumed that users didn’t need an index, since they could simply search the electronic documents, and they didn’t want to pay the extra cost for an index whose inclusion was considered questionable. However, as anyone familiar with online information retrieval knows, search on full-text has severe drawbacks. The user retrieves only matching words and phrases, thus missing synonyms, while also retrieving different instances of a word with different meanings (homographs) and mere passing mentions or negated concepts. The user may retrieve too many inappropriate results to easily sift through. A professionally created index overcomes all of these problems plus has additional features of suggesting related concepts of interest (See also), indicating with the reference is to an image or illustration, instead of text, providing guidance on preferred term usage, etc.
There are methods and tools for creating actual hyperlinked ebook indexes. However, they are not yet adopted by many ebook publishers. Furthermore, there are multiple ebook format standards, as used on different e-readers, so there is no single method to create an ebook index, and ebook index for one format may not work for another. Finally, an index is only as good as the skill of its indexer, and professional indexers are struggling with the new software options (requiring additional skills and expenses) to choose from for ebook indexing. Thus, many qualified indexers have not branched into ebook indexing. The Digital Publications Indexing SIG, through its website resource links and associate member discussion groups, aims to help indexers determine and learn the best methods for creation of ebook indexes. The Digital Publications Indexing SIG also aims to educate publishers of the benefits of and methods for creating indexes for ebooks.