When adding microdata to my sites, I use the vocabulary at schema.org.

At the moment, I use <http://schema.org/SoftwareApplication> to markup software. Since the format is a bit underspecified at schema.org (for instance, what is the difference between `url`, `downloadUrl`, and `installUrl`?), I also had a look at [the Google page about this vocabulary](https://support.google.com/webmasters/answer/1645432?hl=en).

That made me sad.

It turns out that schema.org and Google use two incompatible versions of the 'same' vocabulary. Some differences:

* `fileSize` is given in kB according to schema.org, but in bytes according to Google.
* `operatingSystem` at schema.org is called `operatingSystems` at Google.
* `applicationCategory` at schema.org is called `softwareApplicationCategory` at Google. <rant>...and Google says that the value 'must be one of the supported software application types', but the link to these types is broken.</rant>

Now, to be fair, Google claims that their format is an 'extension' of the schema.org format (but don't you need a new itemtype URL then?), but surely no extension can *redefine existing property names* (like `fileSize`).

What should webmasters do about this? It feels like the right thing to do is to follow schema.org. Is there any consensus on this topic?

(I just came up with a hypothesis: Maybe schema.org is the current version, and the obsolete Google pages were written before schema.org was created, and has simply been left untouched (possibly forgotten) since then?)