Expand the documentation to state that CDS Services are encouraged to take advantage of the capability provided by CDS Hooks of accessing required data through the provided FHIRServer endpoint. Similarly, CDS Clients are encouraged to provide accessible FHIRServer endpoints for CDS Services to consume. Add a "usageRequirements" element to the Discovery endpoint to allow services to characterize their usage requirements (such as requiring access to a FHIRServer) Currently, the expectation is that a cds service should be capable of querying a FHIR server to obtain information it requires and didn't receive over prefetch.  Overall, the emphasis on service's ability to use widely available REST APIs is important, because it both places responsibility and provides flexibility to the service for data accessed. If we create a mechanism by which a service mandates one method over another, clients will be forced to support both equivalently. It doesn't make sense for clients to support the same data breadth and search param complexity in prefetch that's in REST.