This document is intended to contain examples possible of persistent identifier strings and their pros and cons.

Issues

Components of the URI

An example showing different paths for different representations of a resource as an alternative to content negotiation

Jon: why is it necessary to have multiple paths (commons/record, commons/html, and commons/xml)? There seems to be concern that content negotiation is the equivalent of polysemy (one name, many meanings), but this adds another component to every identifier, and we anticipate that only a relative few of our identifiers will offer more than one form of representation
From URI-based Naming Systems for Science

http://purl.org/commons/record/ncbi_gene/24866
denotes an Entrez Gene record "without commitment as to representation" - that is, the record's declarative content independent of whether the record is rendered as XML, ASN, or RDF. The information in the record may change over time as annotations are added and corrections are made, but it will always be about the same "gene" (a term that unfortunately is not defined).
http://purl.org/commons/xml/ncbi_gene/24866
denotes the XML version of the record.
http://purl.org/commons/html/ncbi_gene/24866
denotes a web page presenting information from the record in human-readable form.

Layering to achieve branding without having branded identifiers

Registering a domain name, directing it to purl.org (CNAME), and basing identifiers on the registered name
From URI-based Naming Systems for Science

http://purl.obofoundry.org/obo/OBI_0000225 = http://purl.org/obo/OBI_0000225; both reference http://ashby.csail.mit.edu/cgi-bin/obiterm?ref=OBI_0000225

Jon: This might be a way for a collection to continue its own branding when publishing otherwise meaningless persistent identifiers, as for example registering the domain name handle.ecommons.cornell.edu and directing it to http://hdl.handle.net, so that a URL in the form http://handle.ecommons.cornell.edu/1813/734 could be published instead of http://hdl.handle.net/1813/734; both would resolve to http://ecommons.cornell.edu/handle/1813/734