What properties do schema.org vocabularies require?

People have asked what properties are required for schema.org vocabularies, but (afaik) there’s been no official answer. Here’s what I’ve discovered from the Google Rich Snippets Testing Tool (← link to test file), the closest thing we have to guidance on implementing schema.org vocabularies. Note the tool’s warnings may or may not be according to schema.org vocabularies, as none of this is actually defined (sigh). You could also try referring to Rich Snippets documentation or asking on the mailing list.

Not many properties are flagged as required. This means if you’re changing from <time pubdate> to BlogPosting’s datepublished, (amazingly) you only need to declare the vocabulary and this single property. At least until the vocabulary is updated :)