DMN17 — Frequently changing Namespace URIs cause market fragmentation

Currently, the version of DMN used in an DMN XML file is identified by the XML namespace URI, which is therefore changed with every revision. However, frequently changing namespace URIs cause market fragmentation across supported specification versions, as it cannot be assumed that all vendors update to the latest version of the spec at the same time, if at all.

This forces users to do unnecessary version migrations, or their models would be rejected by a tool as invalid or outdated even though language features used in the model may be perfectly supported by the tool. This issue has also been recognized by Specification Common Elements (SCE) in SCE-117.

With DMN shipping bugfixes on a yearly pace, the fragmentation of the tool market increases, while the actual number of changes to the XML schema decreases. In fact, DMN 1.6 has zero changes to the XML schema at all but if it would follow the "tradition", it would again declare itself totally incompatible with DMN 1.5 and all prior versions.

DMN 1.x revisions have been following the backwards compatibility guidelines for machine-readable files and XML schemas as defined in the OMG Policy for Versioning of Specification URIs, File URIs, and XML Namespaces (smsc/2018-08-01). Therefore, DMN 1.x revisions should not change the namespace URL until a version 2.0 introduces breaking changes, which is not planned at the moment.

The "tradition" to always change the namespace has somewhat accidentally grown:

• DMN 1.1 had to legitimately change the namespace because the XML serialization from DMN 1.0 was unimplementable and required breaking changes
• DMN 1.2 had to change the namespace because the one from DMN 1.1 did not conform to OMG's policy (due to last-minute bad advice from the technical director at the time)
• DMN 1.3 jumped on that to abuse it as a version indicator
• DMN 1.4, DMN 1.5, and DMN 1.6 followed to be "consistent with the scheme"

Add version attribute and use fixed XML namespace URLs

To separate XML namespace and DMN version indicator, DMN adopts a similar mechanism as defined by SCE-117 and used by SDMN-138:

1. Employ fixed XML namespace URIs for better tool interoperability (without a dated version stamp as permitted by section 3.1.2 and annex A of the OMG Policy for Versioning of Specification URIs, File URIs, and XML Namespaces (smsc/2018-08-01)).
2. To indicate which exact version of DMN is used, a new dmnVersion attribute is added. FEEL when used inside DMN follows that version, since mixing different DMN and FEEL versions is not allowed. If FEEL is used in other languages, e.g. BPMN, a version number is added to the URL
3. As an additional aid for tools to find the right XML schema, it recommended to add an xsi:schemaLocation attribute that points to the correct schema file, which is hosted by OMG at a fixed location (see example in revised text).
4. For the XML schemas representing OMG's Diagram Interchange (DI) specification DMN will reuse the XSD files provided by OMG's Specification Common Elements (SCE) as these have been cleaned-up but are semantically identical.