But what happens when InDesign exports to EPUB? I'm happy to report that it does exactly what it should and converts those keywords into
dc:subjectelements in the OPF file:
Now, I'm no expert on metadata, so I have not made it a point to use standard BISAC book categories for describing the subject of my books in those fields. We'll come back to this.
When you upload your book to Apple's iBookstore, you have the option of entering BISAC data in iTunes Producer:
And that data entered in iTunes Producer overrides whatever you entered in the content.opf file (or InDesign for that matter). When someone downloads your book, they will only see the Main BISAC category (although the original keywords remain in the content.opf file inside the book):
And as far as I can tell with this single example (though I've heard other anecdotal evidence also in support), the iBookstore does not use the keyword metadata to help aid searches for your book. Notice for example a search for GREP, which I specified as one of the keywords for this book:
iBookstore fails to return my book when searching for "GREP", even though the book contains "GREP" as a subject keyword.
For the record, my book does appear when searching for "InDesign" and "EPUB", presumably since those words are also in the title.
Then I switched over to Amazon to check what happens there. I also had to enter the BISAC categories when uploading my book to Amazon. In addition, they let me enter up to 7 keywords.
Amazon doesn't list a category next to a book on the Kindle. When I search for InDesign and EPUB, my book appears (as it should, since those words are in the name). More importantly, when I search for "GREP" on Amazon, my book also appears:
Now, I am not at all sure whether Amazon is paying attention to my specified
dc:subjectelements or more probably to the keywords that I specified above. But either way, it gets points for finding the book.
Seems like you can't hurt anything by adding the metadata in InDesign and/or directly in the EPUB file, but it is far from conclusive whether or not it helps. I wonder if other ebook distributors pay attention to the
dc:subjectelements. Does anybody know?
Finally, Apple iBookstore clearly has a long way to go towards being a useful tool for discovering books you're interested in. That it completely ignores metadata categories and gives you no other method for specifying them is pretty lame, to say the least.