...
Note that the default namespace declaration on line 2 technically make the elements Ontology (lines 6 and 7) and Class (lines 9 and 11) into the fully qualified IRIs http://www.w3.org/2002/07/owl#Ontology and http://www.w3.org/2002/07/owl#Class, respectively, however, the use of any other non-OWL, unqualified XML element would inadvertently put that element into the OWL namespace, which is a violation of best practices for data governance generally, and goes against practices outlined in various W3C Recommendations and other documents, including but not limited to Cool URIs for the Semantic Web .
In order to ensure that no every XML element is inadvertently put into the wrong correct namespace, every IOF ontology MUST NOT declare a default namespace (such as the one on line 2, above). Expressed another way, every occurrence of “xmlns” MUST be followed by a colon (“:”) and a namespace prefix (such as the ones on lines 3 and 4).
...