Google has completed updated its article structured data guidelines in the developer section. The guidelines have been completely rewritten to highlight the differences between article markup for AMP and normal HTML pages.
Aaron Bradley discussed these changes on Google+.
“The difference between rich results for AMP and non-AMP pages is now explicitly described
Previously the article data type specifications applied specifically to AMP, and essentially described how to make articles eligible to appear in AMP carousels.
Now Google says "your page is eligible for different features depending on how you code your page": AMP with structured data, or "non-AMP webpage with structured data".
There are now separate illustrations for the rich results generated by each use case: AMP carousels for AMP, and "non-AMP pages can be shown as a rich result in a rich result list, or in a carousel of similar non-AMP pages."
The new guidelines now very explicitly state the requirement that AMP have structured data to be eligible for rich results: "without structured data, AMP pages can appear only as standard blue links in Google Search results."
Property use now described separately for AMP and non-AMP pages
Previously a property was either required or recommended, irrespective of page type. Now each property's usage requirements are governed by whether it's an AMP page or not. For example, the image property is required by AMP, but only recommended for non-AMP pages. There are now, in fact, no required properties for non-AMP pages.
There's now a new category of usage for properties, "ignored". This is universally a property annotation that appears for non-AMP pages, and applies to most properties that are used by AMP: of the 17 properties enumerated only five are recommended, with the remainder being ignored.
TL;DR? Structured data use for articles is now heavily focused on content provided in AMP.”