Mandating xsi type attribute in a xml schema
Note that the prefixes are used only as a placeholder and must be expanded by the namespace-aware XML parser to use the actual namespace bound to the prefix.
But in this case, if say, the schema is modified by making some local declarations global and/or making some global declarations local, then all instance documents are affectedand the instance is no longer valid.
Regardless of what we choose, the entire instance would be validated. , we are specifying that all the elements and attributes in the instance must have a namespace, which in turn adds namespace complexity to instance.
If say that the schema is modified by making some local declarations global and/or making some global declarations local, then the instance documents are not affected at all.
One can choose to use a prefix ABC for the XML Schema namespace, which is legal, but doesn't make much sense.
Using meaningful namespace prefixes add clarity to the XML document.