docs: System taxonomy creation doc updated with Dynamic tags approach

docs/decisions/0012-system-taxonomy-creation.rst

@@ -33,23 +33,25 @@ We have two ways to handle Tags creation and validation for System-defined Taxon
 #. If the tags don't change over the time, you can create all on a fixture (e.g Languages). 
 #. If the tags change over the time, you can create all on a migration. If you edit, delete, or add new tags, you should also do it in a migration.
 
-**Free-form tags**
+**Dynamic tags**
 
-This taxonomy depends on a core data model, but simplifies the creation of Tags by allowing free-form tags,
-but we can validate the tags using the ``validate_object_tag`` method. For example we can put the ``AuthorSystemTaxonomy`` associated with
-the ``User`` model and use the ``ID`` field as tags. Also we can validate if an ``User`` still exists or has been deleted over time.
+Closed Taxonomies that depends on a core data model. Ex. AuthorTaxonomy with Users as Tags
+
+#. Tags are created on the fly when new ObjectTags are added.
+#. On Tag.external_id we store an identifier from the instance (eg. User.pk).
+#. On Tag.value we store an human readable representation of the instance
+    (eg. User.username).
+#. Resync the tags to re-fetch the value. 
 
 
 Rejected Options
 -----------------
 
-Tags created by Auto-generated from the codebase
+Free-form tags
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-Taxonomies that depend on a core data model could create a Tag for each eligible object. 
-Maintaining this dynamic list of available Tags is cumbersome: we'd need triggers for creation, editing, and deletion.
-And if it's a large list of objects (e.g. Users), then copying that list into the Tag table is overkill.
-It is better to dynamically generate the list of available Tags, and/or dynamically validate a submitted object tag than
-to store the options in the database.
+Open Taxonomy that depends on a core data model, but simplifies the creation of Tags by allowing free-form tags,
+
+Rejected because it has been seen that using dynamic tags provides more functionality and more advantages.
 
 .. _document number 0013: https://github.com/openedx/openedx-learning/blob/main/docs/decisions/0013-system-taxonomy-auto-tagging.rst