An Atom is not clear
An Atom must be meaningfulThe example clinical case that is often used is that clearly one would not just communicate the systolic-blood-pressure, and often it isn’t even enough to simply pair up systolic and diastolic taken at the same time, as one may also need to know if this is a resting BP, exercising BP, drug induced BP, or drug-influenced BP and what was the body position of the patient. Further it can be important to know if this data was gathered by a calibrated machine, drug-store machine, trained professional, etc. These are not metadata, these are critical components of the clinical-fact; aka the smallest Atom that can be communicated.
FHIR Atom is a Resource
Metadata. – there is also pointers (a form of metadata) to the patient identity, provider identity, setting, etc…
XDS Atom is a Document
FHIR Atoms can make Documents
FHIR can also be the 'last mile' API to XDS, XCA, and XDR.