DOC: Link to RecordType docs

src/doc/Data-Model.md

@@ -62,4 +62,6 @@ parents are being checked by the Server. Missing obligatory Properties
 invalidate the transaction and result in an error, by default. Missing
 Properties, when they are recommended, result in a warning, but the
 transaction is considered valid. Entities with missing suggested
-Properties are silently accepted as valid.
+Properties are silently accepted as valid. See [the detailed
+specification of RecordTypes](specification/RecordType) for more
+information on importances and inheritance.