The FHIR documentation feels a lot like Wikipedia. You start in one place and end up somewhere completely different.
Here’s my attempt to cut through all of that and highlight 7 key concepts I think every FHIR beginner should try to understand quickly.
1. DomainResource and Resource
Almost all of the 140+ FHIR resources inherit (or extend) from DomainResource, which itself inherits from Resource. These base resources contain common elements such as id, meta, and extension.
2. Resource References
FHIR resources rarely exist in isolation. Resources connect to each other via Resource References, which are links to other resources. Usually — but not always — on the same FHIR server.
Each CodeableConcept represents a single ‘Concept’ or entity that is represented by one or more ‘Code’ or terms. This is one of the most common and important data types in FHIR.
4. An Element’s Cardinality
This tells you how many of an element there can be. Take Condition as an example. It MUST contain one and ONLY one ‘subject’ element (1 .. 1). And there can be any number of ‘identifier’ elements, even none (0 .. *).
5. Is-Modifier Elements
Some elements are considered so important that you can’t safely ignore them. Any code you write must look at and handle all the values in Is-Modifier elements.
6. _include and _revInclude Query Parameters
It’s rare you’ll write a FHIR query that returns only a single resource. The _include and _revInclude parameters give you easy access to resources linked to and from the resource you’re looking for.
7. GET, POST and PUT requests
Gets, creates or updates a FHIR resource. In code or via an API client such as Postman. There’s also a PATCH request, but you can ignore that for a while. 🙂
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