[FIX] wrong usage of DOI in SourceDatasets example

[sappelhoff]

xref: bids-standard/bids-examples#339

Correcting a BIDS-URI example --> relative paths for BIDS-URIs do not start with a file:// ... we use file:// only for absolute paths (such as in file:///home/stefanappelhoff/Downloads/myfile.nii)

I think we can consider this a bugfix.

cc @Remi-Gau @effigies

[sappelhoff]

scratch that ... originally I wanted to fix this example (end of sourcedata section):

-{
-  "SourceDatasets": [ {"URL": "file://../../rawdata/"} ]
-}
+{
+  "SourceDatasets": [ {"URL": "../../rawdata/"} ]
+}

However then I realized that:

1. this example is not about BIDS-URIs
2. this example has been introduced into the derivatives branch 4 years ago

So we probably shouldn't change it. At least not without proper deprecation. I would be fine with repurposing this PR to doing the minor typo fix that I committed in ee02f1c

... but we can also use this space to discuss whether we find it problematic that:

1. In BIDS-URIs, relative paths do not have a leading file://
2. for SourceDatasets relative paths, this is recommended
3. In all other places (I hope) we have deprecated relative paths in favor of BIDS-URIs

A proper fix may be to permit BIDS-URIs for SourceDatasets and to RECOMMEND using them when relative paths are in play. Much like permitting a field BIDS-URI next to the permitted fields URL, DOI, and Version for SourceDatasets. What do you think?

[codecov]

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[DimitriPapadopoulos]

According to 4.3. URL writing:

A relative-URL string must be one of the following, switching on base URL’s scheme:

• A special scheme that is not "file"
  • a scheme-relative-special-URL string
  • a path-absolute-URL string
  • a path-relative-scheme-less-URL string
• "file"
  • a scheme-relative-file-URL string
  • a path-absolute-URL string if base URL’s host is an empty host
  • a path-absolute-non-Windows-file-URL string if base URL’s host is not an empty host
  • a path-relative-scheme-less-URL string
• Otherwise
  • a scheme-relative-URL string
  • a path-absolute-URL string
  • a path-relative-scheme-less-URL string

Therefore, a relative URL cannot start with file://. Instead, a path-relative-scheme-less-URL like ../../rawdata/ is valid.

But then, I don't know if it works here...

[effigies]

Per today's call: The fix is just to drop file:// when it shows up with relative paths. This is not a spec change, just a fix for examples.