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= 1.8 FHIR Overview [http://www.hl7.org/implement/standards/fhir/overview.html#root [[Image:target.png]]] =

Welcome to the FHIR (Fast Healthcare Interoperability Resources) Specification, which is a standard for exchanging healthcare information electronically. This page provides an overview of the standard, and serves as a road map for first-time readers of the specification to help find your way around FHIR quickly.

== 1.8.1 Background ==

Healthcare records are increasingly becoming digitized. As patients move around the healthcare eco-system, their electronic health records must be available, discoverable, and understandable. Further, to support automated clinical decision support and other machine based processing, the data must also be structured and standardized. (See [http://www.hl7.org/implement/standards/fhir/change.html Coming digital challenges in healthcare])

HL7 has been addressing these challenges by producing healthcare data exchange and information modeling standards for over 20 years. FHIR is a new specification based on emerging industry approaches, but informed by years of lessons around requirements, successes and challenges gained through defining and implementing HL7 v2, v3 and the RIM, and CDA. FHIR can be used as a stand-alone data exchange standard, but can and will also be used in partnership with existing widely used standards. (See [http://www.hl7.org/implement/standards/fhir/comparison.html Comparing FHIR to other HL7 standards])

FHIR aims to simplify implementation without sacrificing information integrity. It leverages existing logical and theoretical models to provide a consistent, easy to implement, and rigorous mechanism for exchanging data between healthcare applications. FHIR has built-in mechanisms for traceability to the HL7 RIM and other important content models. This ensures alignment to HL7’s previously defined patterns and best practices without requiring the implementer to have intimate knowledge of the RIM or any HL7 v3 derivations. (See [http://www.hl7.org/implement/standards/fhir/comparison.html Comparing FHIR to other HL7 standards])

== 1.8.2 Components ==
The basic building block in FHIR is a [http://www.hl7.org/implement/standards/fhir/resources.html Resource]. All exchangeable content is defined as a resource. Resources all share the following set of characteristics:

* A common way to [http://www.hl7.org/implement/standards/fhir/resources.html define] and [http://www.hl7.org/implement/standards/fhir/formats.html represent] them, building them from [http://www.hl7.org/implement/standards/fhir/datatypes.html data types] that define common reusable patterns of elements
* A common set of [http://www.hl7.org/implement/standards/fhir/resources.html#metadata metadata]
* A [http://www.hl7.org/implement/standards/fhir/narrative.html human readable] part

== 1.8.3 Approach ==

=== 1.8.3.1 Approach to information modeling ===
The philosophy behind FHIR is to build a base set of resources that, either by themselves or when combined, satisfy the majority of common user cases. FHIR resources aim to define the information contents and structure for the core information set that is shared by most implementations. There is a [http://www.hl7.org/implement/standards/fhir/extensibility.html built-in extension mechanism] to cover the remaining content as needed. 

FHIR modeling uses a composition approach. In comparison, HL7 v3 modeling is based on "model by constraint" (see [http://www.hl7.org/implement/standards/fhir/comparison.html Comparing FHIR to other HL7 standards]). With FHIR, specific use cases are usually implemented by combining resources together through the use of [http://www.hl7.org/implement/standards/fhir/references.html resource references].

*[http://www.hl7.org/implement/standards/fhir/conformance.html Conformance Statement] – describes the interfaces that an implementation exposes for exchange of data
*[http://www.hl7.org/implement/standards/fhir/profile.html Profile] - provide additional rules that serve to constrain the optionality, cardinality, terminology bindings, data types and extensions defined in the resources used by the implementation

== 1.8.4 The Specification ==

Broadly, the FHIR specification is broken up into 3 parts:

* General [http://www.hl7.org/implement/standards/fhir/documentation.html documentation] that describes how [http://www.hl7.org/implement/standards/fhir/resources.html resources are defined], and gives background material including definitions of [http://www.hl7.org/implement/standards/fhir/datatypes.html data types], [http://www.hl7.org/implement/standards/fhir/terminologies.html codes], and the [http://www.hl7.org/implement/standards/fhir/xml.html XML] and [http://www.hl7.org/implement/standards/fhir/json.html JSON formats]
* [http://www.hl7.org/implement/standards/fhir/implementation.html Implementation] - how to use resources using [http://www.hl7.org/implement/standards/fhir/http.html REST], [http://www.hl7.org/implement/standards/fhir/messaging.html Messaging], as [http://www.hl7.org/implement/standards/fhir/documents.html clinical documents], or in a [http://www.hl7.org/implement/standards/fhir/services.html service based architecture]
* The [http://www.hl7.org/implement/standards/fhir/resourcelist.html resource list] - a list of all the resources defined by FHIR. You can also get lists for [http://www.hl7.org/implement/standards/fhir/clinical.html clinical], [http://www.hl7.org/implement/standards/fhir/administration.html administrative] and [http://www.hl7.org/implement/standards/fhir/infrastructure.html infrastructural] resources

Resources have a wide range of uses, from pure clinical content such as [http://www.hl7.org/implement/standards/fhir/careplan.html care plans] and [http://www.hl7.org/implement/standards/fhir/diagnosticreport.html diagnostic reports] through to pure infrastructure such as [http://www.hl7.org/implement/standards/fhir/messageheader.html Message Header] and [http://www.hl7.org/implement/standards/fhir/conformance.html conformance] statements. They all share common technical characteristics (see below for a more formal definition), but they are used in totally different fashions. Note that you do not have to use REST to make use of resources.

== 1.8.5 Where to Start ==
The best place to start is to quickly read the [http://www.hl7.org/implement/standards/fhir/resourcelist.html Resources] list to get a sense of what resources exist and then look at the [http://www.hl7.org/implement/standards/fhir/patient.html Patient resource] definition to see what resource definitions look like, and then read these background pages:

* [http://www.hl7.org/implement/standards/fhir/resources.html Resource Definitions] - basic background to how resources are defined
* About Resources: the [http://www.hl7.org/implement/standards/fhir/narrative.html Narrative] they all contain, and how [http://www.hl7.org/implement/standards/fhir/references.html Resources refer to each other]
* [http://www.hl7.org/implement/standards/fhir/formats.html Formats]<nowiki>: </nowiki>[http://www.hl7.org/implement/standards/fhir/xml.html XML] and [http://www.hl7.org/implement/standards/fhir/json.html JSON]
* About [http://www.hl7.org/implement/standards/fhir/extensibility.html Extensibility]<nowiki>: a key way that the specification is kept simple</nowiki>
* If you are coming to FHIR with a background in another HL7 standard (v2, v3 or CDA), [http://www.hl7.org/implement/standards/fhir/comparison.html The Relationship between FHIR and other HL7 Standards] may also be useful

== 1.8.5.1 Header Tabs ==
These header tabs found through-out the specification are important, and many readers miss them:

[[Image:header-tabs.png]]

Resources and the [http://www.hl7.org/implement/standards/fhir/datatypes.html data types] that they use are presented in an concise easy to read XML-like format, but they also have formal definitions that describe their contents in considerable detail. In addition, most resources are mapped to several different formats, including HL7 v2, the HL7 v3 RIM, CDA, DICOM, and others. Also, all resources come with at least one example (sometimes many more) and, where appropriate, with profiles that describe their use in specific circumstances. Finally, some resources include notes that helps implementers understand the design rationale underlying them.

== 1.8.6 Style conventions ==
This document uses some simple style conventions: <code>this content represents information that may go over the wire</code> ''this is the name of a data element''

== 1.8.7 Finding Additional Information and Providing Feedback ==

While intended to be consumable by a variety of audiences, the FHIR specification is targeted to the implementation community - those who will actually write the software that uses the specification. To help meet the needs of the implementation community, the editors have strived to keep the specification concise to reduce the amount of reading that must be done before writing useful code. (The specification isn't nearly as brief as we'd like - sometimes the complexity of healthcare and the real world get in the way.) For this reason, information that is not essential to the implementation process, such as rationale, considered alternatives, points of contention, future plans, etc. have been excluded from this specification. As well, it is likely that from time-to-time, implementers will encounter situations where the specification is unclear or incomplete. Finally, there will be circumstances where the specification may be broken or where a change could allow it to better meet implementer needs.

HL7 has therefore provided a number of mechanisms through which additional information about FHIR can be sought and maintained and through which support and requests for change can be made.

=== 1.8.7.1 Comments ===

Each page includes a "comments" section at the bottom of the page where questions and discussion about that particular portion of the FHIR specification can occur. The comments will be actively monitored by FHIR editors and HL7 work groups, so questions should be answered in a fairly timely fashion. This content will occasionally be currated to ensure ongoing relevance, particularly if the specification is subsequently updated to eliminate confusion that may have spawned an initial comment.
=== 1.8.7.2 The FHIR Wiki === 
The FHIR project team also maintains a [http://wiki.hl7.org/index.php?title=FHIR wiki] where development processes, methodology and design decisions are documented. Implementers and others can also contribute to the wiki to provide additional guidance and supplemental information not found in the specification. Note that wiki content is not authoritative and is not relevant for determining conformance to the FHIR specification. As well, some wiki content may not be up to date with the most recent version of the FHIR specification.

A wiki page exists for each page in the FHIR specification. These pages will generally be used to capture background rationale, decision points and other information not relevent to implementers. Additional pages defined include [http://wiki.hl7.org/index.php?title=FHIR_Development_Process FHIR methodology], use of the [http://wiki.hl7.org/index.php?title=FHIR_Guide_to_Authoring_Resources FHIR design tools], etc. To explore the FHIR wiki, you can start at the [http://wiki.hl7.org/index.php?title=FHIR root page]

=== 1.8.7.3 Formal Change requests === 

Formal requests for change can be submitted [http://gforge.hl7.org/gf/project/fhir/tracker/?action=TrackerItemAdd&tracker_id=677 here]. (There's a link at the bottom of each page as well.) These will be reviewed by the appropriate work group and a decision made on their incorporation into the specification, including which release (if any) they will be part of.

=== 1.8.7.4 Additional Information sources/Engagement Mechanisms === 

In addition to the above mechanisms, HL7 provides a Stack Overflow tag, list servers and mass Skype chats to provide various levels of implementer support and engagement. Instructions for accessing these other mechanisms (and instructions for how best to make use of them) can be found [http://wiki.hl7.org/index.php?title=FHIR#More_help_and_Asking_Questions here].