Where can I find XSD Schema files for PDF/A XMP metadata?

Question

I am trying to validate the XMP Metadata that are contained in PDF and PDF/A files. Unfortunately, it proved very hard to find the actual XSDs for most namespaces. Is there an official resource pool from Adobe where I could find them?

In special, I am looking for these namespaces:

http://www.aiim.org/pdfa/ns/id/
http://purl.org/dc/elements/1.1/
http://ns.adobe.com/xap/1.0/
http://ns.adobe.com/xap/1.0/mm/
http://ns.adobe.com/pdf/1.3/

Many thanks in advance for all hints.

Answer 1

Missing in the main adobe portal (https://developer.adobe.com/xmp/docs/XMPSpecifications/) but is still accessible here https://archimedespalimpsest.net/Documents/External/XMP/XMPSpecificationPart1.pdf