A namespace is a unique URI that distinguish an XML Web Service from another. The default namespace specified by a 4D Web Service is http://www.4d.com/namespace/default.
A URI does not need to be a valid URL even though most of the namespaces specified in XML Web Services on the web look like URL's. So in order to make your web service unique, you need to customize this namespace. For example, you can use as part of your namespace:
In order to customize your namespace, you need to open the preferences panel at the Web/Web Services page and modify the Web Services Namespace textfield.