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https://www.hl7.org/fhir/STU3/structuredefinition.html
description
Resources returned by the Aggregated FHIR endpoint form a combined data set, drawn from multiple upstream data sets.
This extension captures information about the upstream information that led to the aggregated resource.
The extension has two nested elements:
upstream-source-id. Indicates which data set the resource came from.
upstream-resource-id. Indicates the ID of the resource in the upstream data set.
context
This extension is used by many resources.
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