RDF/XMP generated by pikepdf is incorrect?

[jkorinth]

I use pikepdf to set dc:title, dc:created and dc:contributor metadata on a PDF file. The resulting RDF looks like this (reformatted for better readability):

<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="pikepdf">
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
  <rdf:Description rdf:about="">
    <dc:contributor xmlns:dc="http://purl.org/dc/elements/1.1/">
      <rdf:Bag>
        <rdf:li>Test Contributor</rdf:li>
      </rdf:Bag>
    </dc:contributor>
  </rdf:Description>

  <rdf:Description rdf:about="">
    <dc:title xmlns:dc="http://purl.org/dc/elements/1.1/">
      <rdf:Alt><rdf:li xml:lang="x-default">Title</rdf:li></rdf:Alt>
    </dc:title>
  </rdf:Description>

  <rdf:Description xmlns:dc="http://purl.org/dc/elements/1.1/" rdf:about="" dc:created="D:20231225000000"/>

  <rdf:Description xmlns:xmp="http://ns.adobe.com/xap/1.0/" rdf:about="" xmp:MetadataDate="2024-01-19T07:45:50.786293+00:00"/>
  <rdf:Description xmlns:pdf="http://ns.adobe.com/pdf/1.3/" rdf:about="" pdf:Producer="pikepdf 8.10.1"/>
</rdf:RDF>
</x:xmpmeta>

RDF is an overengineered mess, but judging from what I gather from the specification this is wrong:

1. There can be multiple rdf:Descriptions in a RDF, but I think they need to refer to different things using rdf:about; setting rdf:about to "" may be conformant, but I don't think it is correct. UPDATE: "" is apparently correct to reference the same file; nevertheless, all examples I could find use a single rdf:Description.
2. I'm not sure if dc:created exists as an attribute on rdf:Description, I think it should be an element instead.

I think this would be the correct RDF for the example above:

<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="pikepdf">
<rdf:RDF
      xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
      xmlns:dc="https://purl.org/dc/elements/1.1">
  <rdf:Description rdf:about="">
    <dc:title>
      <rdf:Alt><rdf:li xml:lang="x-default">Title</rdf:li></rdf:Alt>
    </dc:title>

    <dc:contributor>
      <rdf:Bag>
        <rdf:li>Test Contributor</rdf:li>
      </rdf:Bag>
    </dc:contributor>

    <dc:created rdf:datatype="http://www.w3.org/2001/XMLSchema#dateTime">
      2023-12-25T10:00:00Z
    </dc:created>
  </rdf:Description>

  <rdf:Description xmlns:xmp="http://ns.adobe.com/xap/1.0/" xmp:MetadataDate="2024-01-19T07:45:50.786293+00:00"/>
  <rdf:Description xmlns:pdf="http://ns.adobe.com/pdf/1.3/" pdf:Producer="pikepdf 8.10.1"/>
</rdf:RDF>
</x:xmpmeta>