Create Frictionless pattern to support conditional constraints

[niconoe]

In GitLab by @peterdesmet on Sep 25, 2020, 14:25

Conditional constraints are not supported by Table Schema (see frictionlessdata/datapackage#169).

So to support:

scientific_name = required if observation_type = "animal"

We would have to extend the schema as suggested in https://stackoverflow.com/a/38781027/2463806, i.e. (if I interpret this correctly) adding the following at the end of observations-table-schema.json:

"anyOf": [
  {
    "properties": {
       "observation_type": { "const": "animal" }
    },
    "required": ["scientific_name"]
  }
]

Or (using the JSON Schema (draft-07)):

"if": {
  "properties": {
    "observation_type": { "const": "animal" }
  },
  "required": ["observation_type"]
},
"then": { "required": ["scientific_name"] }

But in my understanding, it wouldn't be picked up by any of the Table Schema validators, so it's probably not worth adding and just leave scientific_name not required.

[peterdesmet]

Another option would be to suggest conditional constraints as a new pattern to Frictionless. We would then have to define how conditional constrains should be specified (the syntax) and have tools such as Frictionless Framework implement it.