http://build.fhir.org/subscription-definitions.html#Subscription.filterBy

http://build.fhir.org/subscriptiontopic-definitions.html#SubscriptionTopic.resourceTrigger

http://build.fhir.org/subscriptiontopic-definitions.html#SubscriptionTopic.canFilterBy

Related discussion from connectathon: https://chat.fhir.org/#narrow/stream/179229-subscriptions/topic/Sept.202020.20Virtual.20Connectathon/near/209591241

It's not clear today between Subscription and SubscriptionTopic which criterias or filters apply to which qualifying resources. We need to reorganize the fields to make this more clear.

Proposal:

• Add resourceType to Subscription.filterBy to be able to associate filters with resource to which it applies. Change resourceType to 0..1
• Move canFilterBy under SubscriptionTopic.resourceTrigger, make resourceTrigger 0..*