Why aren't codelists specified as XMLSchema enumeration restrictions? about iati-schemas

[andylolz]

Seems worth tagging @davidmegginson and @Bjwebb here, since I guess this was an early design decision.

[davidmegginson]

Thinking back 9 years, I'm pretty sure it was because schemas and vocabularies are maintained separately. The schema can change without a change in the vocabularies, and vice-versa, so we didn't want to hard-code the vocabularies into the schemas. Also, initially many (most?) of the vocabularies were maintained by the OECD DAC people, not IATI, and a good number still have outside maintainers (for example, OCHA controls some of the humanitarian vocabularies).

Using XSD was a hard decision for other reasons. RelaxNG is a much-more flexible schema language, which would allow us to have elements until iati-activity appear in any order -- it seemed stupid to force a spurious validation error on an XML dataset just because someone put sector and transaction in the wrong (arbitrarily-chosen) order. But we knew that XSD had much-wider tool support, especially in commercial products, and didn't want to throw up a different barrier for users.

[jpmckinney]

Makes sense!

In terms of versioning schemas and codelists separately: The vocabularies can be xsd:import'ed into the schema (as they are in the EU example). To not fix a given version of the schema to a specific version of a given vocabulary, the vocabulary URL can redirect to the latest allowed version for that schema.

Anyhow, I don't know if this is something worth considering for future versions of IATI, or if the status quo is good enough and an infrequent pain-point.