Originally Posted by BenChen
I hadn't heard of ONIX, and after a short amount of googling, I am of the opinion that ONIX is a completely separate standard of ebook metadata. So, I don't know the answer to your question. However, an epub file is simply a zip file with a different extension, so you could certainly put the ONIX info in a file and put it inside the epub file. It's just that no current program would know what to do with it!
Thanks for getting back to me.
Interesting that it never appeared on your radar before. I think that's true for many, and reflects an odd disconnect in publishing. Metadata is essential to discoverability, to ecommerce, to librarians, etc. and in an all-digital world it makes sense -- to me at least -- to keep metadata in the same place as "content" data. Amazon insists on receiving ONIX as does Apple for the iBookstore.
Currently they're separate, and ONIX is very unevenly supported among smaller publishers (although everyone agrees that it is THE standard for book metadata). But no one appears to have considered making it a part of ePub 3. (It presumably was considered, but for some reason not pursued.)
I'm going to the IDPF meeting in New York in 10 days, so I'll learn more there.
Thanks and best wishes with your software and your books.