Instantiation extensions

Prior versions of FHIR had standard elements and extensions named 'instantiatesCanonical' and 'instantiatesUri'. These were intended to link Request and Event resources to the Definition resources they were based on.

These elements have now been replaced by a number of distinct elements that are more specific about the exact nature of the relationship between Request/Event and Definition. This section provides additional guidance about how to decide which relationship to use - and what to do if the level of granularity conveyed by these extensions isn't known in the data source.

• 'generatedFrom' is the most straight-forward. It is *only* used when a Request resource is algorithmically generated (by human or software) from the base Definition resource. In most cases a resource 'generatedFrom' a definition will also have a 'compliesWith' relationship (as it's unusual to generate from a definition and not end up compliant with it). However, because of modifications, it's possible to start out compliant and not end that way. It's also possible to comply with a definition without having been algorithmically generated from it.
• 'compliesWith' and 'adheresTo' are similar. However, they apply to different types of resources. 'compliesWith' is for Request resources and means that the event(s) resulting from the Request (if executed as requested) will align with the expectations of the Definition. On the other hand, 'adheresTo' is for Events and is a direct assertion that the event aligns with the expectations of the Definition. In both cases, the data elements within the request/event have alignment with the definition.
• 'triggeredBy', on the other hand, doesn't indicate anything about the data elements in the Request or Event. It merely indicates that the Request or Event resource came into existence because the Definition said the action was necessary. It's possible for protocols to define that certain events need to exist without describing exactly what they need to look like. It's also possible to describe the details of resources without defining when they need to be created.
• 'shallComplyWith' only occurs for Request resources and is a shortcut for defining the data elements in the Request. Instead of providing details about the code, product, timing, dose, etc., the Request simply includes a reference to the Definition and says "do what it says". The obligation is placed on the system fulfilling the Request to determine how to follow the protocol.

If the specific type of instantiation isn't explicit in a mapped element from a previous release or external specification, the meaning(s) can often be determined by looking at the data, the type of resource, and business conventions. 'compliesWith' and 'adheresTo' can in principle be validated. 'shallComplyWith' will appear on requests that have minimal detail about execution. If it's not possible to determine which extension, the inter-version extensions mechanism can be used to propoagate the old-style extension into a newer FHIR release or a custom extension can be used.

Additional guidance on these extensions

External references might be an HTML page, PDF, etc. or could just be a non-resolvable URI identifier. The display extension ) on canonical can be used to convey the title of the referenced artifact in addition to (or in place of) the discrete elements referencing it.