Subresource is a technical term for properties of a resources that are themselves surfaced as separate resources. The term “subresource” may be useful for people developing the the REST API, but I think the term is confusing to people consuming the API and would prefer that we not use it so much in our documentation.
Metadata could be thought of as “data about data” or “supporting data” or “system data”. Examples may help:
|Bob is right-handed.
||A person can be right-handed, left-handed, or ambidextrous.
|Eve’s temperature is 37°C
||Temperature is measured in centigrade and can be between 25 & 43
|Wyclif’s encounter in Clinic A
||The hospital has clinics: Clinic A, Clinic B, and Clinic C
Trying to say it another way, data are information about a patient and metadata are information about the data we collect. The supporting information of encounter types, concepts, locations, etc. are types of metadata. The information we collect about patients (observations, encounters, notes, etc.) are data. When you are looking at the data model, you’ll see data can be deleted (voided); metadata cannot be deleted once used (if you recorded encounters at a location last week, deleting the location would invalidate all those data), but metadata can be retired to keep it from being used going forward (when a concept, location, or other metadata are retired, it means it should no longer be used but does not invalidate any data previously collected using those metadata).