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[Feedback on schema.org] why is the expected type for "image" not an "ImageObject"?

From: François Daoust <francois@joshfire.com>
Date: Mon, 12 Dec 2011 11:29:51 +0100
Message-ID: <CAFZhi7yCqp4u6nvNCZ-Ce4vQKiZobmB38sgU895gQwJvxbfB8g@mail.gmail.com>
To: public-vocabs@w3.org

I have been playing a bit with the hierarchy defined in schema.org.
Great schema! I have the following related couple of comments.

A Thing [1] has four properties. One of them is "image". The expected
type for this property is a URL. I do not understand why the expected
type is not ImageObject [2]. Other parts of the schema that reference
an image (or a media object) expect an ImageObject. For instance:
- a CreativeWork [3] has an "audio" property that expects an
AudioObject, a "video" property that expects a VideoObject and an
"encodings" property that expects a MediaObject.
- a WebPage [4] has a "primaryImageOfPage" property that expects an ImageObject.
- a Place [5] has a "photos" property that expects an ImageObject (or
a Photograph).
- the "thumbnail" property of an ImageObject expects an ImageObject as well.

I would guess that the main reason to have a URL for the "image"
property is to stick to a "simple" Thing. But that does not look
consistent with the rest of the schema. Is there a good reason not to
expect an ImageObject?

The documentation mentions that URLs may be used in any case for
property values no matter what the expected type might be [6].
Couldn't this fallback mechanism simply be used for Web pages that
simply want to mark an image without going into details about its
author and other metadata?

The second related comment is on "thumbnail" and "thumbnailUrl". Here
the schema does differentiate between URLs and ImageObject. A
CreativeWork defines a "thumbnailUrl" property that expects a URL. The
"thumbnail" property that expects an ImageObject is only defined in

In short, I wonder whether the schema could be updated:
1. to expect an "ImageObject" for the "image" property (or to define
an additional property for that purpose)
2. to replace "thumbnailUrl" with "thumbnail" (or to add a "thumbnail"
property whenever "thumbnailUrl" is defined)

Did I miss something obvious?

Francois Daoust.

[1] http://schema.org/Thing
[2] http://schema.org/ImageObject
[3] http://schema.org/CreativeWork
[4] http://schema.org/WebPage
[5] http://schema.org/Place
[6] http://schema.org/docs/gs.html#schemaorg_expected
Received on Monday, 12 December 2011 12:32:03 GMT

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