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.)
Using productontology.org to add Multiple Types?
microdata;productontology.org;json ld
Your use of additionalType in the first snippet is correct.An example where additionalType is used can be seen on Schema.orgs 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 dont have to come from the same vocabulary.