Add the concept of Blob Reference Properties ("reference attributes" and "reference fields") to the spec

[michaelsafyan]

Fixes #1428

Changes

Adds the concept of "reference attributes" / "reference fields" to the specification.

Merge requirement checklist

• CONTRIBUTING.md guidelines followed.
• Change log entry added, according to the guidelines in When to add a changelog entry.
• [N/A] schema-next.yaml updated with changes to existing conventions.

[michaelsafyan]

Given the existence of the use of ref in the VCS attributes, I will update this PR with an alternative segment.

[michaelsafyan]

Here are some possible naming alternatives to ref:

• external: given that it will be in external storage
• ext: shorter way of using the name "external"
• foreign: given that it is in a foreign storage location
• remote: given that it may be in another storage location
• ext_storage: similar mash up of the above
• remote_storage: similar mash up of the above
• blob_ref: another possible name

Any other thoughts? Any opinions on what is best?

[michaelsafyan]

I've updated the pull request to use *.blob_ref.* instead of *.ref.* but am open to alternative naming suggestions.

[christophe-kamphaus-jemmic]

I think blob_ref is a good choice.

Should there be some tooling to make sure we don't accidentally define anything blob_ref.* in the future?
Eg. could we add a policy in policies/ to flag a violation if blob_ref.* is detected?

[jsuereth]

Policy looks great!

Looking for more input from @open-telemetry/specs-semconv-maintainers

[michaelsafyan]

Received feedback in Nov 18 SemConv Meeting that this PR needs to be amended to remove "attributes" from the scope, because of the possibility of encouraging large attributes.

Was also suggested to narrow scope to define a specific event type that contains its values as a reference.