With the power to share comes the responsibility to share well. Scenarios around sharing are a bit trickier than one might think. I like the idea of putting schema.org metadata (microdata) around the share event.
This: https://developers.google.com/+/history/ is Google+ History

The way I think of it is:
A- Public activity about public URLs
B- Public activity about private URLs
C- Private activity about public URLs
D- Private activity about private URLs

Scenarios A & C are easy: you write a moment into History with a URL pointing to the entity (a place, an event, a track, a book, etc) that was the object/target of the activity. For example <Ade read http://www.amazon.com/Apprenticeship-Patterns-Guidance-Aspiring-Craftsman/dp/0596518382 >

Scenarios B & D are tricky. These scenarios mean we can't reveal the URLs to googlebot (for instance if a URL is behind an authentication screen) so we have to do googlebot's job: extract out the microdata from the page and write it directly to History.

This is handled by this: https://developers.google.com/+/history/#moments_and_results part of the API which lets you pass in a 'result' as part of the Moment you write to History. Here's an example of one of those result objects: https://developers.google.com/+/history/api/moments#reviewactivity The algorithm for extracting this microdata (or for just creating it without first building a private web page) are defined as part of the HTML5 spec: http://dev.w3.org/html5/md/#json

Most of the talk about History that I've seen has revolved around scenarios A & C. Hopefully this post will get people thinking about new possibilities.
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