A Profile for Define-XML

As the CDISC XML Technologies team finalizes Define-XML v2.1 for internal review an old debate has re-surfaced: how much should the Define-XML specification focus on the regulatory submissions use case versus providing a more general specification that works for a broader set of use cases. As a standard that provides metadata to describe tabular datasets, Define-XML can be used to describe legacy datasets as well as datasets included for submissions. Define-XML has also been used as a specification for datasets. However, Define-XML became the most widely implemented ODM-XML based standard due its role as a required element of regulatory submissions. The importance of ensuring that Define-XML files included in a submission are complete and accurate makes a compelling case for adding rules that specifically target this use case at the risk of reducing its usefulness in other contexts.

Having recently participated in the September HL7 FHIR connectathon in Baltimore, MD it strikes me that the notion of profiling, as it is described for FHIR resources, would provide a good solution for Define-XML. Profiling is where the base resources are adapted for specific use cases. The FHIR specification describes a growing set of base resources that can be used in many different healthcare contexts making FHIR a “platform specification.” It is expected that the platform specification will require adaptations in the form of profiles to meet the needs of specific use cases. Profiles can be used to both constrain and extend resources. They describe the rules that specify which data fields are required vs. optional and which coding systems are used in the stated context. Validators ensure that a specific resource instance conforms to the profile.

Creating Define-XML as a “platform specification” useful across a broad range of use cases, while also creating a regulatory submission profile and implementation guide would seemingly be an ideal solution. As a platform specification Define-XML can be effectively used across a range of use cases. The definition of a regulatory submissions profile would permit the implementation of a comprehensive set of rules effectively adapting Define-XML for use in submissions without concern that these rules are limiting the usefulness of the base standard.


  1. Interesting thoughts...
    FHIR has always been concipated as an 80/20 solution, having a core set of resources that can be used worldwide and leaving the remaining 20% as "extensions" to account for local circumstances and conditions. For example, core-FHIR does not implement the concept of "race", as there is no worldwide consensus about what "race" exactly means and especially not which races there are.
    This profiling has a long tradition within HL7. Even in HL7-v2, we have the so-called "Z-Segments" allowing for extensions that only have local validity, within a single hospital, organization, or country.
    Essentially, Define-XML is already an extension and restriction (of ODM) at the same time. But we can surely think about how define-XML can be adapted in such a way that it can be also be used in the non-regulatory context. This can indeed be done by different implementation guides for different use cases, probably in combination with several Schematrons for easy and transparent validation.
    HL7-CDA i.m.o. went too far in this. Essentially only a framework was delivered, forcing implementers of real use cases to write hundreds of pages of Implementation Guides. For example, the Austrian ELGA Laboratory Report Implementation Guide is 122 pages and builds upon the "general" Implementation Guide which is 226 pages. Also, the Schematrons that come with these implementations are very complicated.
    Of course, Define-XML is much less complicated, and several implementation guides for several use cases with different schematrons are very well realizable.


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