Using productontology.org to add Multiple Types?

Question

I have recently been reading about productontology.org to define additional types with schema.org to be more specific.

I am building a website for a local pet store that offers various pet products, grooming and training. I have the following code for the site's schema:

<script type="application/ld+json">
{
  "@context": "http://schema.org",
  "@type": "LocalBusiness",
  "additionalType": "http://www.productontology.org/id/Dog_grooming",

  //Additional Schema Markup (opening hours, location, etc.)
}
</script>

As you can see I added an additionalType in the JSON-LD for dog grooming. Can I add multiple additionalTypes if it applies to the business? IE:

"additionalType": "http://www.productontology.org/id/Dog_grooming",
"additionalType": "http://www.productontology.org/id/Dog_training",

Or should I stick with one? In other words, is it allowed or beneficial to add more than one additionalType?

Also, is my usage of additionalType in the JSON-LD correct? (I haven't seen any real examples with additionalType and JSON-LD.)

Answer 1

Your use of additionalType in the first snippet is correct.

An example where additionalType is used can be seen on Schema.org’s IndividualProduct:

<script type="application/ld+json">
{
  "@context": "http://schema.org",
  "@id": "#product",
  "@type": "IndividualProduct",
  "additionalType": "http://www.productontology.org/id/Racing_bicycle",
  "description": "ACME Racing Bike, bought 8/2008, almost new, with a signature of Eddy Merckx on the frame.",
  "name": "ACME Racing Bike in black (2008)"
}
</script>

Adding multiple additional types is possible, too. However, not by adding the property multiple times, but, e.g., by using an array:

<script type="application/ld+json">
{
  "@context": "http://schema.org",
  "@type": "LocalBusiness",
  "additionalType": ["http://www.productontology.org/id/Dog_grooming", "http://www.productontology.org/id/Dog_training"]
}
</script>

Adding multiple additional types can of course be beneficial: if multiple types apply, so be it! It would make no sense to arbitrarily limit it to one additional type only.
You can, of course, add types from various vocabularies; they don’t have to come from the same vocabulary.