title_body: Universal Identification metadata for e-books
upvoted_answer: This is a great question, and I don't have any inside knowledge about how search engines interpret metadata for books. 
  
  I checked the source of several book distributors and found that there's an open graph generator for books. http://webcodetools.com/open-graph-generator/book
  
  Librarything, Smashwords and Harper Row publishers embed ebook info in these tags, and possibly more (but not Amazon). 
  
  I don't know if putting things in the meta tag really counts as giving it semantic meaning though.
  
  Also, it's interesting that I don't see anything human readable on Amazon that might resemble this. 
  
  Dublin core metadata is popular for library cataloguing, but I don't think it really offers useful information for search engines http://wiki.mobileread.com/wiki/Dublin_Core
  http://dublincore.org/documents/dces/
  
  Actually when you input metadata for an ebook in Calibre, it generates dublin core data in the metadata.opf file (and you can edit this metadata by right-clicking the epub in Calibre). DB metadata is required and it typically appears in package.opf. Of course, this  standard doesn't seem to be geared to ebooks, and things like ISBN don't translate well for ebooks.  
  
  While logically it makes sense to have metadata for all the ebook distributors, it's unlikely that ebook distributors would carry metadata on its competitors. Publishers and authors are more likely to benefit from embedding this metadata, but what I've seen so far looks very simple (and gives only one URL). 
  
  I am guessing that while you might be able to do ISBN searches across platforms (even for ebooks), this is not especially useful for ebooks. It sounds like  other than fuzzy searches, there is no direct way for a database to be linked to the same ebook on different ebook distributors.  
  
  These are superficial thoughts, but  I would not be surprised if some kind of solution emerges over the next few years.