One thing I wonder about is what the various goals of structured book review content can be. The classic example would be a citation, to make it precisely clear whence one’s quotes originate and whither to search for context. The second obvious example would be a product review; “should you buy this book?”
Schema.org’s Book schema has some fields that spark ideas, but mostly seems like “bookstore dataset” territory.
It’s the possibilities outside all that that get interesting.
- tagging, categories (for personal organization or community use)
- adjacency: “you’d like this if you liked X” or “if you like this, also try Y”
- mentioning someone (with webmention) to note that you think they particularly would like it
- decentralized doesthedogdie.com content warnings
- fan content (we already know fans are powerful and creative folksonomists)
- metadata for interesting indexing/scraping; “here is an illustration of X”
- hell, even “here is a continuation I wrote of X”
- perhaps “this bit is an excerpt/quote of X”?