How to test rules that can't be validated by the schema?

[jonblower]

E.g.:

• A parameter object MUST NOT have a "unit" member if the "observedProperty" member has a "categories" member.
  • Perhaps this should be rewritten "can only have one of "unit" and "categoryEncoding""?
• Check that category ids match the observed property ids
• Check that values of categoryEncoding are all unique
• Lots of stuff in axis - monotonic values, etc

[jonblower]

Maybe we need different schemas for Parameters and observedProperties for continuous and categorical data? Can we use "oneOf" in the schema to capture this perhaps?