As you say, its piggybacking on the dns's uniqueness guarantee. Urls do at least provide and obvious way to have multiple namespaces per domain. But I agree tha

As you say, its piggybacking on the dns's uniqueness guarantee. Urls do at least provide and obvious way to have multiple namespaces per domain. But I agree that it's confusing. I once had the misfortune to have to use a third-party xml-based webservice whos developers thought that the xml namespace had to match the url used to access it. So their production and test systems had completely different namespaces. They maintained multiple xsd schemas for each system that only differed by namespace. When I finally managed to explain namespaces to their "chief web architect" he got all embarrassed. This was back in .net 4.x days, and I was generating serialisation classes from their schemas - so I had to create two different dlls and load the appropriate one at runtime. Very aggravating.