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

	HDL	PURLz
permanent	Yes	Yes
permanently resolve to a digital object	Yes	Yes
unique within our PID system without the DNS name portion of the	Yes; very flexible naming, including pseudo/paths	Yes, but
URL	?	Yes
works with VIVO, arXiv, OAIS (CUL), Voyager Catalog, and WorldCat etc.	Yes	does nothing in and of itself to not work with existing systems;
resolvable through a web browser	Yes	Yes
Simplicity	Yes	Yes
support for a local namespace prefix and an identifier part	Yes	Yes
support for opaque identifiers	Yes	Yes
Local part should not be Cornell branded	completely flexible	Yes
may be surrogate for physical object	Yes	Yes
should be short (so use 26 letters plus numbers)	Yes	Yes
should be easy to copy by hand	depends on the length	depends on the length and/or layout

	HDL	PURLz
Supports billions of identifiers	Don't know; limited to the practical capacity of the underlying database.	Don't know – mention of 1996 tests resolving 50 resolutions/sec with a database of 500,000 PURLS in Long Introduction to PURLs
Robust architecture	Yes	Yes; PURLz is just a simple HTTP server using MySQL
Robust implementation	Yes	No - alpha stage
ability to request metadata about the identifier	Yes	Yes
lightweight understanding of identifier equivalence	Yes	Cloning an existing PURL and chaining a PURL
should be easily discoverable by Google	Yes; the resolvers can't be crawled without providing a dump	Yes; the resolvers can't be crawled without providing a dump
integrate well with the "web architecture"	Yes	Yes
vitality checking	?	not built in
Need to avoid unbounded generation of surrogate persistent identifiers	?	?
PID corresponding to every Cornell NetID	?	Depends on the Partial Redirect working – e.g., http://resolver.cornell.edu/netid/bdc34

	HDL	PURLz
Requires payment to external organization	one-time $50 payment per named resolver (not mirrors)	no
Can continue resolve IDs in absence of external organization	Yes	Yes

HDL is Corporation of National Research Initiatives's Handle system.
PURLz is Zepheira's and OCLC's new persistent URL work.

Uniqueness: We think PURLZ will reject the creation of a duplicate PURL, but we're not entirely sure how it deals with duplication when a PURL name component overlaps a PURL domain component – e.g., if we inadvertently created a domain /a/b/ with resource 1234 and someone later used the name b/1234 in domain /a/. Maybe pure string comparison for non-uniqueness is all that's required, but conventions need to be established to avoid confusion.