Persistent identifiers (Pids) provide machine-actionable links to data and metadata that are vital to APIs (application programming interfaces) for publishing and citation. APIs are essentially request/response patterns that use Pids to reference things and metadata to describe not only the things themselves, but also any actions requested or taken. As a result, metadata design and standardization is wedded to API design and enhancement. With Pids as nouns and metadata as adjectives and qualifiers, Pid services play a key role in API implementation.

1. Persistent Identifier Services and
their Metadata
John Kunze
California Digital Library

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Decoding the title
persistent identifier services and their metadata
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things, actions, and descriptors
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nouns, verbs, and adjectives
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preserving and serving scholarly communication around data
(Context: scholarly research data)
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3. Obama

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An identifier is not a string of characters
An identifier is an association between a string and thing.
An association is an opinion asserted by an authority.
Example 1:
http://allrecipes.com/recipe/sauteed-fiddleheads
Example 2:
4CF3-57AB-2481-651D-D53D-Q
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http://dx.doi.org/10.5072/4CF3-57AB-2481-651D-D53D-Qhttp://dx.doi.org/10.5240/4CF3-57AB-2481-651D-D53D-Q

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Identifier schemes (v1)
• URL (Uniform Resource Locator)
• the first time poor id management is blamed on syntax
• URN (Uniform Resource Name)
• first attempt to correct poor id management with syntax
• Handle
• second attempt to correct poor id management with syntax
• DOI (Digital Object Identifier)
• third attempt to correct poor id management with syntax
• ARK (Archival Resource Key)
• attempt to let id management be queryable (not yet realized)
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Identifier schemes (v2)
• URL (Uniform Resource Locator)
• world’s first actionable id, now underlying all other types
• URN (Uniform Resource Name)
• open infrastructure, not fully realized globally
• Handle
• closed infrastructure, fully realized globally
• DOI (Digital Object Identifier)
• CrossRef enforces good id management, DataCite learning
• ARK (Archival Resource Key)
• open infrastructure, realized locally and globally
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If DOIs won why talk about non-DOIs?
• Cost
• Open access
• Changing nature of the DOI
• Flexibility
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Types of identifier services
• Repository – parking the bits
• Data-aware dissemination
• more than just returning parked bits
• Citation management for end user researchers
• Research tracking – measuring use and impact
• Identifier creation, management, and resolution
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Many service tools, many APIs
Repository Tools
• ArXiv *
• Dataverse *
• Fedora/Hydra
• Dspace *
• Eprints
• DataONE
• Merritt/Stash
• figshare
• Zenodo
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Citation Management
• Mendeley
• Zotero
Metrics and Tracking
• Altmetric
• Impactstory
• Thomson Reuters Data Citation
Index
• Elsevier Scopus

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API concepts
Application Programming Interface (API)
• how software talks to a service
• unlike a Graphical User Interface (GUI)
• more like a Command Line Interface (CLI)
APIs and CLIs use language constructs
• Verbs, nouns, and qualifiers are "words”, and
• words form commands/requests/responses,
• which form scripts and programs.
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APIs are metadata sentences
A command line interface powering an API interaction
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$ sort mydata > sorted_data
$ grep Smith sorted_data
Smith, Sally 2014-04-01 406B
Wong, Frank 2013-11-28 334
$ wget --user=sam --no-check-certificate
"https://n2t.net/a/ezid/b?set cost 25.50"
status: ok

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Problem: traditional standardization
• Change by committee is ugly, costly, and slow
• Example: Dublin Core, 15 cross-domain terms
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European Parliament Technology - DG ITEC @ flickr

13. The Metadata Universe
Jenn Riley,
IU

14. The Metadata Universe
Jenn Riley,
IU

15. The Metadata Universe
Jenn Riley,
IU

16. The Metadata Universe
Jenn Riley,
IU

17. The Metadata Universe
Jenn Riley,
IU

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An alternate metadata universe
• Vision: one dictionary, one namespace
• All research domains, any part of “metadata speech”
• Names, values, units, relationships, ...
• Search for terms, comment on terms, add terms, edit
your terms, API for automated access
• All terms with globally unique persistent identifiers
• Available at yamz.net (yet another metadata zoo)
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YAMZ.net dictionary sociology
• Crowd-sourced evolving vernacular terms, stable
canonical terms, and deprecated terms
• Use evolving terms depending on your risk tolerance
• Reputation-based (gaming-resistant) voting means
strong terms rise, weak terms decline
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Applying lessons learned from Wikipedia, the
Internet-Draft/RFC process, and StackOverflow

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Summary
• Identifiers are not strings, but associations that break
when things are not managed well
• People can forget names because we can google, but
APIs need persistent names for automation at scale
• APIs are languages using metadata as “words”
• Future API building will focus on vocabulary building
• For example, yamz.net
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Thank you!
John.Kunze@ucop.edu