Category Archives: Profiling

Introducing Forge for STU3

DutchKingWedding

Royal tears of joy at the official STU3 release ceremony

Today marks the community release of Forge for FHIR STU3. A joyful moment, right after our national Dutch King’s day and just in time for the upcoming HL7 WGM in Madrid.

Hoera! Hoera! Hoera!

You can download Forge, the FHIR profile editor, for free from the FHIR profile registry at simplifier.net. In this article we’ll introduce you to the new release and try to answer some common questions about migration to STU3.

Side by side installation

The new Forge for STU3 ClickOnce installer package has a new application identity that allows side by side installation. This means that you can install and use Forge for STU3 next to an existing installation of Forge for DSTU2 on the same machine. Each release will use it’s own version of the FHIR core resource definitions and manage it’s own application configuration settings separately.

dutch-king-willem-alexander-with-wife-maxima-and-animal-pelt

Side by side installation

As of now, future application updates will target the Forge STU3 release. You can still use Forge for DSTU2 and remain to keep using it for as long as you need. But from now on, the Forge DSTU2 branch will no longer be actively developed as our development efforts are now focused on the STU3 branch. We will remain to provide support for the final Forge DSTU2 release to our commercial customers until they have migrated to STU3.

Profiling changes in STU3

FHIR STU3 introduces a lot of updated and new resources and datatypes. Changes to the conformance resources have the largest impact on profiling. Fortunately, the main FHIR conformance resources are relatively mature and haven’t changed drastically, with one notable exception in the terminology space: CodeSystem has been separated from ValueSet. However this change has no impact on Forge.

You will notice some relatively minor changes to the StructureDefinition resource and the ElementDefinition datatype. Some properties have been renamed and there are a couple of new properties, e.g. to define FHIRPath expressions.

One of the more notable changes involves ElementDefinition.type.profile. In DSTU2, an element type can define multiple profiles. However there are some complications with this approach:

  1. Multiple type profiles pose a problem for dynamic code generation, UI input form generation etc.
    Note that although Forge for DSTU2 (secretly…) supports specifying multiple profiles per type, all known FHIR DSTU2 implementations actually only consider the primary type profile. Practical use of this technique has been actively discouraged by the FHIR infrastructure group. We are not aware of any customers to rely on profiles having multiple type profiles.
  2. When an element has type ResourceReference, we would like to be able to express constraints on the reference target. However ElementDefinition.type.profile expresses constraints on the ResourceReference itself.

FHIR STU3 solves these problems by:

  1. Introducing ElementDefinition.type.targetprofile wich applies when the type code equals ResourceReference and expresses a constraint on the reference target. As before, you can use ElementDefinition.type.profile to constrain the ResourceReference datatype itself.
  2. Limiting ElementDefinition.type.profile max cardinality to 1. This takes away any ambiguity for e.g. code/UI generation.

FHIR STU3 also introduces a lot of changes to the other (clinical) resources and data types. Forge for STU3 includes a new STU3-specific version of specification.zip that contains updated definitions for all the existing and newly introduced resources and data types in STU3.

Migration to STU3

As FHIR STU3 introduces breaking changes to StructureDefinition and ElementDefinition, Forge for STU3 is not compatible with existing DSTU2 profiles.

It is possible to automatically convert existing DSTU2 StructureDefinition resources to the new STU3 format. However an automatic conversion tool can only update the meta information in the profile. It cannot safely convert the actual profiling constraints. Because STU3 introduces changes to many of the resources, some of the constraints in a DSTU2 profile will no longer be valid when converted to STU3. For example, when a DSTU2 profile constrains an element that has been renamed/removed in the corresponding STU3 resource. Therefore migrating profiles from DSTU2 to STU3 will usually require manual review and corrections.

We have a team of experienced consultants with a track record in FHIR profiling who can assist and support you with smooth profile conversion to STU3. Feel free to contact us for a quote or if you want to learn more about our professional FHIR consultancy services.

King-Willem-Alexander-Queen-Maxima-Princesses-Catharina-Amalia

Dutch royal family is said to be “super excited” about FHIR STU3

Looking back

We’ve come a long way since the first release of Forge. The initial Forge DSTU1 release attempted to provide a reference implementation of the FHIR standard. Our team tried to demonstrate that the basic FHIR (profiling) principles could indeed be implemented and put to use. Forge was originally designed to hide the user from the complexity of the underlying XML/JSON wire representation. The novel UI design quickly drew a small but growing user base and succeeded to stimulate both the adoption as well as the development of the FHIR standard itself.

After updating Forge to DSTU2, we focused our efforts on improving the quality of the generated differential and snapshot components. Implementing a proper and fully capable snapshot generator in the .NET FHIR API library proved to be a (royal pain in the ***) challenging and time consuming undertaking that claimed a great deal of development time during 2016. But those efforts eventually drove the implementation of some very powerful profiling features in Forge, such as support for derived profiles, deep inline constraints on complex extensions and dynamic expansion of choice type elements and properties. It took a fair bit of time and effort to stabilize some of the more complex features. But thanks to feedback from our users and from the FHIR profiling community, we managed to solve most of the reported issues.

Moving from DSTU2 to STU3, we have noticed a clear trend in Forge issue reports where they slowly but steadily involve more and more complex and rare profiling use cases. This indicates that basic FHIR profiling features have indeed matured and stabilized and that our users are starting to apply more advanced profiling techniques. And while these newly reported issues may not always be easy to solve, generally they do seem to confirm that FHIR profiling is proving to be effective and productive!

Looking forward

Now that we have updated our full tooling stack to STU3 (The official FHIR .NET API library; Forge, the FHIR profile editor; simplifier.net, the FHIR profile registry; and last but not least Vonk, our new enterprise-grade FHIR server), we are looking forward to unleash them onto the FHIR community, starting at the upcoming HL7 WGM in Madrid.

Our simplifier.net platform now supports STU3, but will also remain to serve existing DSTU2 profiles. We will cooperate with our Simplifier users in order to provide migration strategies to update existing DSTU2 projects to STU3. Under the hood, our team has updated the simplifier.net environment to the new Microsoft .NET Core platform, which brings a significant performance increase, improved response times and higher scalability. We are experimenting with the new Microsoft Orleans platform, an exciting new cloud-based technology, in order to implement scalable validation support and initial results are quite promising. This will allow our simplifier.net platform to provide computationally intensive features to an ever increasing and demanding user base.

As Forge has been updated to STU3 and most of the underlying complex profiling logic is finished and maturing, we can now focus our development efforts towards improving the user experience, file management, online simplifier integration and profiling workflow support. We have received a lot of great suggestions from the community about possible improvements and new features that will allow us to further improve the application. Your feedback remains very valuable to us, so please don’t hesitate to submit issue reports and/or feature requests! Should you have a need for commercial support, then you may benefit from one of our simplifier.net account plans.

Last but not least, our brand new Vonk server is now ready for STU3. Vonk is a modular and highly scalable FHIR server based on the new Microsoft .NET core platform. Aside from performance improvements, the new platform also enables some surprising new applications, as recently one of our bright engineers successfully managed to spin up a Docker image of Vonk server running .Net core on Linux. The new flexible options for host operating systems ensure that our Vonk server will smoothly integrate into any existing customer infrastructure.

Final thoughts

Kings day

Millions join the Forge STU3 release party, Amsterdam 2017

We hope that you enjoy the new Forge STU3 release, as well as all our other FHIR tools. The Furore FHIR team celebrated this important milestone in Amsterdam on our King’s birthday, which traditionally involves orange outfits, DJ-powered canal boat rides and abundant substance abuse. And now that the orange smoke has cleared up, we’re back making FHIR simple.

 

Download Forge for STU3 for free from simplifier.net

Happy profiling and long live the King!

 

Zo waerlijck helpe my Forge almechtig

 

Forge

Forging Profiles on Profiles

Introduction

Recently (Friday November 25th) we published a new Forge release, Forge 14.4 for DSTU2 – FHIR DevDays 2016 edition. You can download the new Forge release for free from Simplifier.net. The previous Forge release (13.2) dates from June 10th, so clearly it’s been a while since we’ve published an update. In this blog post I’ll elaborate on the most important new feature: support for profiles on profiles, also known as derived profiles.

What is a derived profile?

Out of the box FHIR resources are designed to cover 80% of the common use cases. In order to cover the remaining 20%, FHIR introduces profiles. A FHIR profile defines a set of constraints on a standard FHIR resource or datatype. This allows you to define a specialized variant of a standard resource for a specific use case. And because profiles are based on common FHIR resources, they provide a certain basic level of global interoperability with other (external) FHIR systems.

Obviously, as we limit the context to a specific country, region or organization, we can probably harmonize more aspects and provide increased interoperability within that limited context. FHIR supports this common use case by allowing you to define so-called profiles on profiles a.k.a. derived profiles. A derived profile defines a set of constraints on another existing profile, the so-called base profile. The derived profile implicitly inherits all the existing constraints from the associated base profile. A derived profile can only further constrain the base profile, similar to profiles on core resources.

Example:

  • The HL7 affiliate for the Netherlands publishes a national profile for a Dutch patient. The profile is based on the standard FHIR Patient resource and defines a number of additional constraints, e.g. in order to identify Dutch patients by their unique national social security number (BSN). The profile also constrains the generic Patient.careProvider reference to a specific Dutch practitioner profile.
  • A Dutch hospital authors a derived Patient profile for use within the organization. The organizational Patient profile is based on the national Dutch patient profile and defines some additional constraints that only apply within the organization. The hospital’s custom Patient profile defines additional constraints for the unique Patient identifier that is assigned by the hospital EHR system. The profile also prohibits the Patient.animal element, as it does not apply.
Hierarchy of Profiles

Hierarchy of profiles

As the example demonstrates, this allows you to create a hierarchy of profiles, e.g. on a national, regional, organizational and/or departmental level. As we navigate deeper down the profile hierarchy, we encounter more specific profiles for more limited use contexts.

Authoring a derived profile in Forge

New Derived ProfileUsing the new Forge 14.4 release, you can now easily author a derived profile. Forge 14.4 introduces a new command “New Derived Profile“. You can find the new command directly on the start screen, in the File menu and also in the Session Explorer toolbar. The new command resembles the existing “New Profile” command, but with one important difference: you can select an existing profile as the underlying base profile. Forge will display a File Open dialog window to select a suitable base profile from disk. After selecting the base profile, Forge will create and display the new derived profile.

For example, let’s assume that Mayo Clinic wants to create their own derived Patient profile based on the US DAF Patient profile which defines a set of national constraints for the US Patient. Below, we can see the original DAF Patient base profile loaded in Forge. All the constraints defined by the base profile are clearly indicated by the yellow pen icon:

DAF Patient Profile

Notes:

  • The blue exclamation icon indicates a “must support” element
  • The blue paperclip icon indicates extension elements
  • The yellow pen icon indicates a constrained element

Now Mayo Clinics creates a new derived Patient profile based on the DAF Patient profile. The new derived Patient profile inherits all constraints that are defined by the base DAF Patient profile. Initially, the new derived profile does not introduce any new constraints, as is clearly visible in the Forge Element Tree:

Mayo Clinic Patient Profile

The screenshot demonstrates that the derived Patient profile indeed inherits all the constraints defined by the base DAF Patient profile (e.g. you can see the inherited extensions such as ethnicity). Because the implicitly inherited constraints are not defined by the derived profile itself, they are not considered to be part of it. This is clearly visible in the Forge element tree, as none of the elements in the new derived profile show a yellow pen icon (except on the root element, because the derived profile has a new name & url). In other words, the new derived profile shown above is (almost) empty.

Now Mayo Clinic can define additional specific constraints in the derived profile. Any newly defined constraints will actually be part of the derived profile and consequently they will be indicated by a yellow pen in Forge. For example, the screenshot below shows how the derived profile defines an additional constraint on the Patient.photo element:

Mayo Clinic Patient Profile with constraint on photo

Below you can see the serialized XML of the derived Patient profile. We can clearly see the newly introduced constraint on the Patient.photo element. Note that the root element definition is mandatory in DSTU2, even if the element is not constrained. This requirement will be deprecated in STU3. Also note the (mandatory) reference to the underlying DAF Patient base profile.

<?xml version="1.0" encoding="utf-8"?>
<StructureDefinition xmlns="http://hl7.org/fhir">
  <meta>
    <lastUpdated value="2016-12-01T16:47:22.41+01:00" />
  </meta>
  <url value="StructureDefinition/MayClinicPatientProfile" />
  <name value="Mayo Clinic Patient Profile" />
  <status value="draft" />
  <date value="2016-12-01T16:28:17+01:00" />
  <fhirVersion value="1.0.2" />
  <kind value="resource" />
  <constrainedType value="Patient" />
  <abstract value="false" />
  <base value="http://hl7.org/fhir/StructureDefinition/daf-patient" />
  <differential>
    <element>
      <path value="Patient" />
    </element>
    <element>
      <path value="Patient.photo" />
      <max value="0" />
    </element>
  </differential>
</StructureDefinition>

Conclusion

This concludes our introduction of the new support for derived profiles in Forge. The example demonstrates that the authoring process is actually quite easy for end users and quite similar to creating profiles on core resources. After all, in FHIR we try to move complexity away to the developers of tools and servers.

As simple as this all seems to the end user, the actual implementation entailed a long and winding road straight into the bowels of the FHIR specification. In a separate blog post, I will provide some more in-depth background information about the technical challenges we faced when trying to implement support for derived profiles, and how we addressed these.

If you have questions concerning (derived) profiles or need a bit of assistance, then you are strongly encouraged to join the online FHIR discussion groups. The FHIR community is very active, friendly and helpful and usually you quickly receive helpful responses from FHIR users all over the world. The conformance stream is specifically intended to discuss FHIR profiling and related tools including Forge. Also if you’ve implemented FHIR in a production environment, then please inform the FHIR community and share your story in the implementers stream!

Two final notes:

  1. Today we have published a minor hotfix release (14.4.1) with a couple of bugfixes. Should you encounter any issues while trying to repeat the exercise above, then please make sure that you have upgraded to the most recent version. Users of release 14.4 will receive an auto-update notification. Users of earlier releases should manually download and install the new version.
  2. The new Forge release does not yet support base profiles containing slices. If you select a base profile containing slices, snapshot generation will fail and generate a runtime exception. We will introduce support for sliced base profiles in a future application update.

Happy profiling!

Michel Rutten