Profiles and implementation guides

The base form is generic. Real life is not.

The base FHIR forms are generic on purpose. But countries, settings and organizations differ. That is why FHIR describes itself as a platform specification, one that usually needs adapting.

A profile adjusts a form

The base forms are generic, because they must work in different countries and settings. So FHIR lets a community adjust a form. The specification's own example: a prescription form could have extension elements added to track restricted medications, and the codes for drug types limited to a national standard. Turn it over, and that is a profile. An extension adds an element. A constraint limits the codes, using a value set. And the changes are made in a way that does not change how forms are passed around, so any system can still read the completed form.

From broad to narrow agreements

Adaptations form a cascade. At the top, international base agreements, such as the International Patient Summary. Then national base guides, such as US Core. Then clinical domain and project guides. And at the bottom, vendor and institution guides. Each level makes more agreements with a smaller community. Higher levels are more concerned with meaning, consistent functionality, and are more likely to be freely public. Lower levels are more concerned with which data is present, and local extensions.

• Institution · Vendor and local guides; often not public. · building
• Project · Domain and project guides, e.g. mCode. · target
• National · National base guides, e.g. US Core. · globe
• International · Base agreements, e.g. IPS. · layers

A term, and what it is

Match the term to what it is. An implementation guide is a coherent set of adaptations, published as one unit. A profile is a set of constraints on a resource, written as a structure definition. An extension adds an element the base does not have. A value set chooses which codes are allowed. A capability statement says what an implementation supports. And a structure definition is the resource that describes how a resource, extension or datatype is used.

• Implementation guide · Adaptations published as one unit · file · navy
• Profile · Constraints on a resource · lock · navy
• Extension · An element the base lacks · star · amber
• Value set · Which codes are allowed · check · slate
• CapabilityStatement · What a system supports · gear · slate
• StructureDefinition · How a structure is used · layers · slate

Simple and complex extensions

Every element can have extensions, to carry information the base does not define. An extension is either simple or complex. A simple extension has a value and no nested extensions. A complex extension contains nested extensions and no value. It cannot have both. Applications should not reject a resource merely because it contains extensions.

Check yourself

Pause and think. Why does FHIR need profiles? The answer: it is a platform specification that usually needs adapting to a context.

• It is a platform specification that usually needs adapting to a context
• Because the base specification is incomplete and unusable
• Because each hospital must publish its own standard
• Because resources cannot carry codes

Keep these in mind

FHIR is a platform specification, and contexts adapt it. A profile constrains a resource, and an extension adds to it. Guides cascade from international to institutional. And adjusted forms can still be shared and read.

• FHIR is a platform specification; contexts adapt it
• A profile constrains a resource; an extension adds to it
• Guides cascade from international to institutional
• Adjusted forms can still be shared and read