Which resource is a definition of a FHIR structure?

• A. StructureDefinition
• B. ImplementationGuide
• C. SearchParameter
• D. GraphDefinition

Answer: (A)

StructureDefinition is the resource that defines the shape and constraints of a FHIR resource or datatype. It specifies which elements exist, their data types, cardinalities, bindings, and any constraints, and it can represent how a base resource is profiled or how an extension is structured. In other words, it is the formal definition of a FHIR structure, capturing its schema and rules.

The other resources have different roles: ImplementationGuide provides guidance on how to implement and deploy FHIR in a given context; SearchParameter defines how to search resources (the parameters and behavior for queries); GraphDefinition describes how resources relate to each other in a graph view or traversal.