Clarify statements around CDS Service performance and stale data (fixes #221) (#369)

Clarify statements around CDS Service performance and stale data (fixes #221)

- Remove requirement that CDS Services must perform on the order of 500ms
- Remove requirement that EHR must supply the latest EHR data

Both of these requirements were not feasible or technically possibly under all scenarios.

Author: kpshek

docs/specification/1.0.md

@@ -162,11 +162,11 @@ curl
 
 ## Providing FHIR Resources to a CDS Service
 
-Each CDS Service will require specific FHIR resources in order to compute the recommendations the EHR requests. If real-world performance were no issue, an EHR could launch a CDS Service passing only context data, and the CDS Service could then request authorization for  FHIR resources as they were needed, and then retrieve the resources from the EHR's FHIR server.  However, CDS Services must respond quickly (on the order of 500 ms.), and so we provide performance enhancements that allow a CDS Service to request and obtain FHIR resources more efficiently. Regardless of the method used to provide FHIR resources to a CDS Service, the EHR must assure that clinical data provided to the CDS Service are the most current data available to the EHR user.  Decisions based on stale clinical data pose a safety threat to the patient and must be avoided.
+Each CDS Service will require specific FHIR resources in order to compute the recommendations the EHR requests. If real-world performance were no issue, an EHR could launch a CDS Service passing only context data, and the CDS Service could then request authorization for FHIR resources as they were needed, and then retrieve the resources from the EHR's FHIR server.  Given that CDS Services SHOULD respond quickly (on the order of 500 ms.), this specification defines a process to allow a CDS Service to request and obtain FHIR resources efficiently.
 
-Two optional enhancements are provided.  First, FHIR resources may be obtained by passing "prefetched" data from the EHR to the CDS Service in the service call.  FHIR resources requested in the CDS Service desciption are passed as key-value pairs, with each key matching a key described in the CDS Service description, and each value being a FHIR resource. If data are to be prefetched, the CDS Service registers a set of "prefetch templates" with the EHR, as described in the [Prefetch Template](#prefetch-template) section below.
+Two optional methods are provided.  First, FHIR resources may be obtained by passing "prefetched" data from the EHR to the CDS Service in the service call.  FHIR resources requested in the CDS Service desciption are passed as key-value pairs, with each key matching a key described in the CDS Service description, and each value being a FHIR resource. If data are to be prefetched, the CDS Service registers a set of "prefetch templates" with the EHR, as described in the [Prefetch Template](#prefetch-template) section below.
 
-The second enhancement enables the CDS Service to retrieve FHIR resources for itself, but to do so more efficiently than if it were required to request and obtain its own authorization.  If the EHR decides to have the CDS Service fetch its own FHIR resources, the EHR obtains and passes directly to the CDS Service a bearer token issued for the CDS Service's use in executing FHIR API calls against the EHR FHIR server to obtain the required resources.  Some EHRs may choose to pass prefetched data, along with a bearer token for the CDS Service to use if additional resources are required.  Each EHR may decide which approach, or combination, is preferred, based on performance considerations and assessment of attendant security and safety risks. For more detail, see the [FHIR Resource Access](#fhir-resource-access) section below.
+The second method enables the CDS Service to retrieve FHIR resources for itself, but to do so more efficiently than if it were required to request and obtain its own authorization.  If the EHR decides to have the CDS Service fetch its own FHIR resources, the EHR obtains and passes directly to the CDS Service a bearer token issued for the CDS Service's use in executing FHIR API calls against the EHR FHIR server to obtain the required resources.  Some EHRs may choose to pass prefetched data, along with a bearer token for the CDS Service to use if additional resources are required.  Each EHR may decide which approach, or combination, is preferred, based on performance considerations and assessment of attendant security and safety risks. For more detail, see the [FHIR Resource Access](#fhir-resource-access) section below.
 
 Similarly, each EHR will decide what FHIR resources to authorize and to prefetch, based on the CDS Service description's "prefetch" request and on the provider's assessment of the "minimum necessary."  The EHR provider and the CDS Service provider will negotiate the set of FHIR resources to be provided, and how these data will be provided, as part of their service agreement.