Make sure to specify item information, otherwise Google will not index structured data on your website.
Button name is an identifier to which votes are being connected. It must be unique for each button, otherwise the same voting will be reflected to all the buttons having the same name.
Item information is used for sharing the item in social networks and for displaying the rating in Google Rich Snippets.
(Used in Google Rich Snippets only. The date and time the item was published, in ISO 8601 format: 2017-06-27T08:00:00+08:00)