I have to model a product, which has properties that aren't listed in the Schema.org Product type. After seeking in many places, I didn't find anything that fits to my need.
How can I extend the Schema.org Product type?
You could always use other vocabularies (that offer the properties you need) in addition to Schema.org. But if you want to use only the vocabulary Schema.org, you have two options in general:
Propose new properties (or classes).
You can do this on Schema.org W3C Community Group’s mailing list, or on Schema.org’s GitHub issue tracker.
See: How can I get involved? How can I propose new schemas or other improvements?
If accepted, it might become part of the core (if it’s something "the most common web applications need"), or it might become an extension.
(deprecated!) Extend existing properties.
Extending existing properties is documented at http://schema.org/docs/old_extension.html, but note that this mechanism is considered outdated.
For specific types (including Product), you can use Schema.org’s additionalProperty property:
A property-value pair representing an additional characteristics of the entitity, e.g. a product feature or another characteristic for which there is no matching property in schema.org.
来源：https://stackoverflow.com/questions/27581209/schema-org-how-to-extend-a-class-or-type