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For Identifiers (just the complete URI and local part, not about mechanisms)

	HDL	PURLz
permanent	Yes	?
permanently resolve to a digital object	Yes	?
unique within our PID system without the DNS name portion of the	Yes; very flexible naming, including pseudo/paths	?
URL	?	?
works with VIVO, arXiv, OAIS (CUL), Voyager Catalog, and WorldCat etc.	Yes	?
resolvable through a web browser	Yes	?
Simplicity	Yes	?
support for a local namespace prefix and an identifier part	Yes	?
support for opaque identifiers	Yes	?
Local part should not be Cornell branded	completely flexible	?
may be surrogate for physical object	Yes	?
should be short (so use 26 letters plus numbers)	Yes	?
should be easy to copy by hand	depends on the length	?

For Resolver and System

	HDL	PURLz
Supports billions of identifiers	Don't know; limited to the practical capacity of the underlying database.	?
Robust architecture	Yes	?
Robust implementation	Yes	?
ability to request metadata about the identifier	Yes	?
lightweight understanding of identifier equivalence	Yes	?
should be easily discoverable by Google	Yes; the resolvers can't be crawled without providing a dump	?
integrate well with the "web architecture"	Yes	?
vitality checking	?	?
Need to avoid unbounded generation of surrogate persistent identifiers	?	?
PID corresponding to every Cornell NetID	?	?

Governance Issues

	HDL	PURLz
Requires payment to external organization	one-time $50 payment per named resolver (not mirrors)	?
Can continue resolve IDs in absence of external organization	Yes	?

HDL is Corporation of National Research Initiatives's Handle system.
PURL is OCLC's PURL system.
PURLz is Zepheira's and OCLC's new persistent URL work.
HNRS is the Harvard Name Resolution Service.
DOI is IDF's DOI system.