📝 Add a short section on ISO/IEC 5230/OpenChain

docs/productive/licensing.rst

@@ -287,14 +287,33 @@ Alternatives
 `ClearlyDefined <https://clearlydefined.io/>`_
     It collects and displays information about the licensing and copyright
     situation of a software project.
-`OpenChain <https://www.openchainproject.org/>`_
+:ref:`open_chain`
     It recommends REUSE as a component to improve the clarity of the licensing
     and copyright situation, but has more stringent requirements to achieve full
     compliance.
 `FOSSology <https://www.fossology.org/>`_
     Free software compliance toolkit that stores information in a database with
     license, copyright, and export scanners.
 
+.. _open_chain:
+
+ISO/IEC 5230/OpenChain
+----------------------
+
+`ISO/IEC 5230 <https://en.wikipedia.org/wiki/ISO/IEC_5230>`_ is based on the
+`OpenChain Specification 2.1
+<https://github.com/OpenChain-Project/License-Compliance-Specification/raw/master/2.1/en/openchainspec-2.1.pdf>`_
+and is an international standard on software supply chains, simplified
+procurement and open source licence compliance.
+
+.. seealso::
+
+   * `OpenChain project <https://www.openchainproject.org>`_
+   * `OpenChain Self Certification
+     <https://certification.openchainproject.org>`_
+   * `Reference-Material
+     <https://github.com/OpenChain-Project/Reference-Material>`_
+
 Python package metadata
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