How to use OAI-PMH API, oai.datacite.org/oai, for DOI metadata downloading?

OAI-PMH API oai.datacite.org/oai allows you to download DOI metadata in XML. OAI-PMH stands for Open Archives Initiative - Protocol for Metadata Harvesting.

Query parameters supported by oai.datacite.org/oai are:

verb - Required. The verb of the query action: ListIdentifiers, ListSets, ...
from - Optional. The start date of the DOI registration date range.
until - Optional. The end date of the DOI registration date range.
set - Optional. The container of DOI records.
identifier - Optional. The DOI.
metadataPrefix - Required for ListIdentifiers and ListRecords. 
  The Metadata Format code.

oai.datacite.org supports only 4 OAI verbs, ListRecords, ListSets, ListMetadataFormats, and ListIdentifiers

1. ListMetadataFormats - Returns a list for supported data formats, which are: oai_dc, oai_datacite and datacite.

2. ListSets - Returns a list of sets that act as containers of DOI records.

3. ListIdentifiers - Returns a list of DOIs.

4. ListRecords - Returns a list of DOI records.

Here is an example of downloading DOIs updated on 2022-10-01:

fyicenter$ curl 'https://oai.datacite.org/oai?verb=ListIdentifiers&from=2022-10-01&until=2022-10-01&metadataPrefix=oai_dc'

<?xml version="1.0" ?>
<?xml-stylesheet type="text/xsl" href="/static/oaitohtml.xsl"?>
<OAI-PMH xmlns="http://www.openarchives.org/OAI/2.0/" 
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
  xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/ http://www.openarchives.org/OAI/2.0/OAI-PMH.xsd">
  <responseDate>2022-10-11T01:43:50Z</responseDate>
  <request verb="ListIdentifiers" metadataPrefix="oai_dc" 
    until="2022-10-01T23:59:59Z" from="2022-10-01T00:00:00Z">https://oai.datacite.org/oai</request>
  <ListIdentifiers>
    <header>
      <identifier>doi:10.13130/di-candia-domenico_phd2011-01-19</identifier>
      <datestamp>2022-10-01T18:38:11Z</datestamp>
      <setSpec>TQID</setSpec>
      <setSpec>CRUI.UNIMI</setSpec>
    </header>
    <header>
      <identifier>doi:10.13130/invernizzi-simone_phd2011-05-31</identifier>
      <datestamp>2022-10-01T20:37:59Z</datestamp>
      <setSpec>TQID</setSpec>
      <setSpec>CRUI.UNIMI</setSpec>
    </header>
    <header>
      <identifier>doi:10.13130/vismara-paolo_phd2013-02-08</identifier>
      <datestamp>2022-10-01T18:39:02Z</datestamp>
      <setSpec>TQID</setSpec>
      <setSpec>CRUI.UNIMI</setSpec>
    </header>
    <header>
      <identifier>doi:10.15468/rjarmt</identifier>
      <datestamp>2022-10-01T23:31:48Z</datestamp>
      <setSpec>GBIF</setSpec>
      <setSpec>GBIF.GBIF</setSpec>
    </header>
...

Here is an example of downloading DOI records updated on 2022-10-01:

fyicenter$ curl 'https://oai.datacite.org/oai?verb=ListRecords&from=2022-10-01&until=2022-10-01&metadataPrefix=oai_dc'

<?xml version="1.0" ?>
<?xml-stylesheet type="text/xsl" href="/static/oaitohtml.xsl"?>
<OAI-PMH xmlns="http://www.openarchives.org/OAI/2.0/" 
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
  xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/ http://www.openarchives.org/OAI/2.0/OAI-PMH.xsd">
  <responseDate>2022-10-11T01:57:09Z</responseDate>
  <request verb="ListRecords" metadataPrefix="oai_dc" until="2022-10-01T23:59:59Z" from="2022-10-01T00:00:00Z">https://oai.datacite.org/oai</request>
  <ListRecords>
    <record>
      <header>
        <identifier>doi:10.13130/di-candia-domenico_phd2011-01-19</identifier>
        <datestamp>2022-10-01T18:38:11Z</datestamp>
        <setSpec>TQID</setSpec>
        <setSpec>CRUI.UNIMI</setSpec>
      </header>
      <metadata>
        <oai_dc:dc xmlns:dc="http://purl.org/dc/elements/1.1/" 
          xmlns:oai_dc="http://www.openarchives.org/OAI/2.0/oai_dc/" 
          xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/oai_dc/ http://www.openarchives.org/OAI/2.0/oai_dc.xsd">
          <dc:title>RILIEVO DI FATTORI XENOBIOTICI, CON PARTICOLARE RIFERIMENTO A NICOTINA E COTININA, ...</dc:title>
          <dc:creator>DI CANDIA, DOMENICO</dc:creator>
          <dc:publisher>Università degli Studi di Milano</dc:publisher>
          <dc:date>2011</dc:date>
          <dc:date>Issued: 2011-01-19</dc:date>
          <dc:description>RESEARCH OF XENOBIOTIC FACTORS, ESPECIALLY OF NICOTINE E COTININE, ...</dc:description>
          <dc:language>it</dc:language>
          <dc:type>Text</dc:type>
        </oai_dc:dc>
      </metadata>
    </record>
...

⇒ GraphQL API - api.datacite.org/graphql

⇐ api.datacite.org/providers - Query Providers

⇑ DataCite.org DOI Database

⇑⇑ DOI - Frequently Asked Questions