I mark up a webpage about a book with microdata of Schema.org. With the "about"-property of creativeObject type will mark up the book topics. The "about"-property has like expected type a Thing.
My questions are:
Is it right, that here i can use instead of Thing any other, more specific, type, cause Thing is the most generic type?
Is it not a problem, that i use the "about"-property more than once on the page, applied to describe the same creativeObject?
Thanks and best regards
Evgeniy
For your first question:
Is it right, that here i can use instead of Thing any other, more specific, type, cause Thing is the most generic type?
Sure. More than that - you can use just text if you'd like to (I suppose it is more suitable for book topics). I had the same question a time ago and was redirected to docs:
Expected types vs text. When browsing the schema.org types, you will notice that many properties have "expected types". This means that the value of the property can itself be an embedded item (see section 1d: embedded items). But this is not a requirement—it's fine to include just regular text or a URL. In addition, whenever an expected type is specified, it is also fine to embed an item that is a child type of the expected type. For example, if the expected type is Place, it's also OK to embed a LocalBusiness.
For your second question:
Is it not a problem, that i use the "about"-property more than once on the page, applied to describe the same creativeObject?
I don't think it is. Last time it was discussed in schema.org WG it was decided that
Right now, it is always allowed to have multiple values. [for properties]
You can find more here and here. But you should keep in mind that all the details of markup usage depends on the specific consumer (Search Engine, etc).