Datatype entity is missed

[adelavega]

See: https://github.com/bids-standard/pybids/pull/863#discussion_r1026856773

[erdalkaraca]

Datatype is not listed as an entity in the schema. Maybe it makes sense to treat it the same way as extension/suffix, i.e. as an additional property of the Artifact class.

[erdalkaraca]

This will require to extend the Artifact's definition:

Artifact:
  .doc: >-
    An artifact is a file whose name conforms to the BIDS file naming convention.
  .extends: File
  suffix:
    type: str
    use: required
  **datatype:
    type: str**
  entities:
    type: EntityRef
    min: 1
    max: -1

[adelavega]

yes, I did notice that its not in the schema. I think we will need to think about whether datatype should be deprecated or added to the schema to minimize "exceptions"

[effigies]

Datatype is in the schema:

• Definitions: https://github.com/bids-standard/bids-specification/blob/master/src/schema/objects/datatypes.yaml
• Used in file rules: https://github.com/bids-standard/bids-specification/blob/master/src/schema/rules/files/raw/task.yaml

[ghisvail]

I believe you do need datatype to disambiguate multi-modality suffixes such as mask or events for instance.

[erdalkaraca]

What I am not sure about yet is how to handle the datatype in derivatives as files are not required to be in a datatype (sub-)folder. Can we reliably infer the datatype from the suffix in case a file is not in a datatype folder?

[ghisvail]

Can we reliably infer the datatype from the suffix in case a file is not in a datatype folder?

I don't think the BIDS specs ever defined a 1:1 mapping between suffix and datatype tbh.

It took me several read to understand the modality -> datatype -> suffix hierarchy and how it relates to file collections.

It just happens that most modalities define a 1:1:1 between all three so it's easy to make this shortcut. I started to reconsider when I read about events, and then much later when the derivatives specs were refined.

[ghisvail]

in derivatives [...] files are not required to be in a datatype (sub-)folder.

AFAIK, datatype is still listed in the derivatives section of the specs, and all proposed derived types feature one.