“…RFC 2288 [RFC2288] investigated the feasibility of using ISBN, ISSN, and SICI (Serial Item and Contribution Identifier) as URNs, with positive results; however, it did not formally register corresponding URN namespaces. (For further discussion of how these systems have evolved as URNs, see RFC 8254 [RFC8254].) This was in part due to the still-evolving process to formalize criteria for namespace definition documents and registration.…”