Indeed a very good document, but I miss the explicit mentioning of the use of PID’s as linked data URI’s by way of content negotiation. Implicitly content negotiation is hinted at in section 3.4. Resolvable. Subsection3.4.1. states: “There can be two intentions of PID resolution. A PID is resolvable when it allows both human and machine users to access: 3.4.1.1. An object or its representation: This would either allow direct access to its assigned object or representation, or information on how the object can be accessed. 3.4.1.2. Kernel Information: A global resolution system should support access to Kernel Information from its PID.”
A PID resolver should be able to distinguish between a) human and machine users, and b) the requested representations (plural!). This is done by the mechanism of content negotiation, where the resolver decides whether to redirect to a human readable landing page, a specific digital representation/version of the identified object, the metadata about the object in various formats (RDF, JSON, etc.). Linked data services are only possible if one or more RDF formats can be requested.
Currently the main PID systems (Handle, DOI, even ARK) do not support real content negotiation. I think the policy should definitely aim to persuade the relevant PID Authorities to put this on their roadmap.
Lukas Koster
Digital Infrastructure Coordinator
Library of the University of Amsterdam