...
Consider a common 'attributes of an attribute' - the properties of an attribute (e.g unique, authoritative or self reported, time since verified, last time changed, last time accessed, last time consented) that would be released and provide an audit trail.
The local definition of attributes (isn't this semantics not schema?) in any given global schema, the interpretation of metadata and trust frameworks, all of this creates a space where it is very difficult to share information that will meet the expectation of relying parties.
Work in this space
Common language - Schema
Efforts in this space:
...