consistent "URI", "DOI", "URL": guidance on how to ensure an unambiguous link

[Remi-Gau]

DOI or URL basically means URI.
Maybe we can shorten this and give some guidance on how to ensure an unambiguous link?

Originally posted by @effigies in #573 (comment)

See the rest of the thread for more information.

In short:

• trying to have some consistency in the specs on how URI are expressed would be a good thing.
• especially if it can be done in pedagocial way (potentially in synch with the BIDS starter kit) and we can nudge users into providing unambiguous links to resources.

[effigies]

I think we can do this at the top of common principles, under the RFC2119 notice, or as an additional definition, following "File extension". If we want to do the latter:

The relevant RFC for URIs is RFC 3986. Perhaps something like:

1. Uniform Resource Indicator (URI) - A string referring to a resource.
   URIs have the form <scheme>:[//<authority>]<path>[?<query>][#<fragment>], as
   specified in RFC 3986, and include URLs as a subset.
   Other common URIs include Digital Object Identifiers (DOIs), which may be fully
   specified as doi:<path>, for example, doi:10.5281/zenodo.3686061.
   A given resource may have multiple URIs.
   When selecting URIs to add to dataset metadata, it is important to consider specificity
   and persistence.

[Remi-Gau]

Having our own "definition" as part of the spec was another option suggested in #573 .

I am in favor of that.

Should I start a PR? If so, should the scope of the PR to be add that definition AND update the whole specs?

[sappelhoff]

Should I start a PR? If so, should the scope of the PR to be add that definition AND update the whole specs?

PR would be very welcome, and yes the scope sounds good!