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We need a solution for legacy websites incapable of being modified to store the PIDs created; the resolver must be able to assume that the original URL provided for the resource will continue to function, or that some alternative will be provided when the legacy website ceases to respond. This becomes a matter of policy rather than technology.
Migration of current purl system to new resolver
All existing purls must remain functional (number ? 10-20k??, 1800 indexed in Google). No more would be assigned.
Requires server answering purl dns name and forwarding/responding based on information from new resolver. Would require change of existing workflows to stop assigning new purls.