Use of Must Support and Obligations

The FHIR "Must Support" flag on an element (abbreviated as MS) indicates that systems using the associated profile must be able to process the MS element. The exact behavior that is expected is written as narrative text.

FHIR Obligations provide a more fine-grained way to describe the expected behavior associated with an element. Obligations can be more precise, and lend themselves to automated conformance testing.

Note that different actors (such as a Sender and a Receiver) might have different obligations.

This page sets out the PH Core policies related to the use of MS and Obligations.

When MS is used on the top level of a complex element or an element having a complex datatype, the meaning is ONLY that systems must examine the MS / Obligations on the sub-arts of the element. It DOES NOT mean that all actors must support all the sub-elements. For example, if we marked Patient.address as MS, implementers are required to follow the instructions (MS and / or obligations) on Address.line, Address.city, and so on.

If Obligations are used on an element or any part of an element, MS SHALL also be used on that element / part.

If obligations are used on an element or any part of an element, MS SHALL be used at the top level of the element.

PH Core authors are encouraged to use the most specific obligations possible to meet their use cases, balancing the need for flexibility at the national level. Many obligations statements might be best reserved for a system-specific or use-case IG. Human-readable documentation of the expected behavior SHOULD be provided.