# Indexing Identifier Services

Where do you look for identifiers?

If you’re looking for a URI, the IANA has a registry of schemes, like https, mailto, and tel.

These days, to resolve an identifier, you generally use the https scheme, which has an authority component in its URI format. You can go with content addressing like IPLD CIDs, but that doesn’t solve where to look – it solves knowing that you found the thing (or that you already have the thing).

Authority is hard to persist. So people and organizations pool efforts towards generic authority under the https URI scheme, like hdl.handle.net, doi.org, n2t.net, identifiers.org, purl.org, w3id.org, wikidata.org, etc. Or they pool towards authority with narrower scope, like orcid.org, ror.org, igsn.org, etc. Or they just pursue lasting authority with a new .org or through a trusted .gov, etc.

How do you index identifiers from various sources? There are efforts like LOV for vocabularies, and Crossref and DataCite for DOIs.

I think OpenAlex is setting a nice example of collecting identifiers from various systems and connecting them, along with descriptive metadata.

What about collecting identifier services? Is this of interest? Is it a fool’s errand due to the rise and fall of authority? Or is tracking and using the rising and falling of reputation and reliability, Google-PageRank-style, a way to shepherd researchers to robust persistence of identifiers?

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