Additional niche properties of products allow studying user preferences and calculate recommendations more accurately. This section describes niche properties for books.

Author

It allows specifying the author of a work, book, etc. The "author" element must be inside the "offer" element.

<offer ...>
    ...
    <author>William Shakespeare</author>
    ...
</offer>

Publisher

It allows specifying the publisher of a work, book, etc. The "publisher" element must be inside the "offer" element.

<offer ...>
    ...
	<publisher>Publisher</publisher>
    ...
</offer>

Series

It allows specifying a series of works. The "series" element must be inside the "offer" element.

<offer ...>
    ...	
	<series>Barnes & Noble Collectible Editions</series>
    ...	
</offer>

Year

It allows specifying the year of publishing. The "year" element must be inside the "offer" element.

<offer ...>
    ...
    <year>2016</year>
    ...
</offer>

ISBN

It allows listing the ISBNs (there may more than one). The "isbn" elements must be inside the "offer" element.

<offer ...>
    ...
    <isbn>918-1-82402-537-0</isbn>
    <isbn>918-0-00-172188-5</isbn>
    ...
</offer>