Question

What is the namespace used for in a SOAP web service?

Answer 1

From http://tempuri.org/:

Each XML Web Service needs a unique
namespace in order for client
applications to distinguish it from
other services on the Web. By
default, ASP.Net Web Services use
http://tempuri.org/ for this purpose.
While this suitable for XML Web
Services under development, published
services should use a unique,
permanent namespace.

Your XML Web Service should be
identified by a namespace that you
control. For example, you can use your
company’s Internet domain name as part
of the namespace. Although many
namespaces look like URLs, they need
not point to actual resources on the
Web.

Say company A and B both create a service with methods of the same signature. In order to differentiate between them you can add a namespace. That would make them different from a client’s perspective, meaning you couldn’t use the wsdl(proxy classes) from one on the other and vice verse.

It’s considered good practice to use a unique namespace for your services. Typically your company name/domain or similar, instead of the default tempuri.org.