Background and Rationale

 
From HREx:
 

All Da Vinci IGs that define [CapababilityStatements](http://hl7.org/fhir/R4/capabilitystatement.html) setting expectations for support for certain FHIR interactions, operations, or other exchange mechanisms *SHALL* include a 'design' section that explains the IG's choice of exchange architecture in terms of the decision tree found in the FHIR core specification.

 
see https://build.fhir.org/ig/HL7/davinci-crd/background.html#architectural-approach
for an example of this.

Proposal

Add "design" section to the backgrounds page for the following exchange architecture:

1. For Direct Query and Task-Based Workflows add the decision tree based explanation here: https://hl7.org/fhir/us/davinci-cdex/background.html#direct-query-and-task-based-workflows
2. For Sending attachments add the decision tree based explanation here: https://hl7.org/fhir/us/davinci-cdex/background.html#unsolicited-attachments-workflow
3. For Requesting attachments refer to the Task-based transaction decision tree discussion 
4. For polling vs subscriptions udpate the section to inlucde the decision-tree discussion here: https://hl7.org/fhir/us/davinci-cdex/task-based-approach.html#polling-vs-subscriptions.