What is the meaning of [ServiceContract(Namespace = "http://Microsoft.ServiceModel.Samples")] in the official WCF tutorial?

Question

I'm trying to follow the official basic tutorial on WCF: https://learn.microsoft.com/en-us/dotnet/framework/wcf/getting-started-tutorial

At one point, when defining the service contract, the tutorial asks us to type the following code:

using System;
using System.ServiceModel;

namespace GettingStartedLib
{
        [ServiceContract(Namespace = "http://Microsoft.ServiceModel.Samples")]
        public interface ICalculator
        {
            [OperationContract]
            double Add(double n1, double n2);
            [OperationContract]
            double Subtract(double n1, double n2);
            [OperationContract]
            double Multiply(double n1, double n2);
            [OperationContract]
            double Divide(double n1, double n2);
        }
}

I am very confused by the ServiceContract attribute, and in particular, by the weird namespace: http://Microsoft.ServiceModel.Samples

What is this namespace?

I was trying to search the documentation of the ServiceContractAttribute, but I still fail to understand what is going on here:

By default, the Name and Namespace properties are the name of the contract type and http://tempuri.org, respectively, and ProtectionLevel is ProtectionLevel.None. It is recommended that service contracts explicitly set their names, namespaces, and protection levels using these properties. Doing so accomplishes two goals. First, it builds a contract that is not directly connected to the managed type information, enabling you to refactor your managed code and namespaces without breaking the contract as it is expressed in WSDL. Second, explicitly requiring a certain level of protection on the contract itself enables the runtime to validate whether the binding configuration supports that level of security, preventing poor configuration from exposing sensitive information. For more information about protection levels, see Understanding Protection Level.

What is this namespace? What should I set this attribute to? Any string that I like? A string in any particular format? What should I take into account when deciding what to put there?

Both examples (http://Microsoft.ServiceModel.Samples and http://tempuri.org) suggest I should enter an HTTP address. But what HTTP address? Am I supposed to operate a server under this address that will do something meaningful? What should this server do? Because, based on these examples and on the fact that http://tempuri.org is allowed (even though not recommended) I understand that this namespace is not expected to be set to the address of my WCF service? (otherwise, I understand, http://tempuri.org would not even work on a sample locally hosted WCF service because the service is not hosted on tempuri.org but on localhost!`

And what is http://Microsoft.ServiceModel.Samples??? Is it even a valid HTTP address? If so, in what format? (When I see http://something I expect this something to be either an IP address or a domain that can be resolved to an IP address with the help of DNS, but Microsoft.ServiceModel.Samples seems to be neither of these two) I even tried entering http://Microsoft.ServiceModel.Samples in my browser, but unsurprisingly, I just got the error Server Not Found.

What is the meaning of this namespace? And what to put there?

Answer 1

The attribute is really designed for the XML that gets generated. Since SOAP is XML based and XML really likes namespaces then SOAP uses them to. In general you don't really need to worry about the namespace because a dummy one will be used. The purpose of this property on the attribute is to allow you to specify an actual XML namespace instead of the default one. Note that this particular attribute only impacts the SOAP definition itself. The service and data will still use the default namespace (you have to attribute them as well if you don't want that).

The purpose of the XML namespace stuff is to separate elements/attributes when working with large XML sets. For a WCF service this isn't going to be an issue but some people like to specify company-specific namespaces anyway. This is really only common in public facing services. For private ones who cares.

So, unless you're building a public service and you want the namespaces to clearly reference your company then you don't need the namespace information. While it is generally given as a URL, it isn't one. It just uniquely identifies the elements/attributes in the XML.( Quoted from the answer to WCF ServiceContract namespaces)

Answer 2

@Theobald Du said "This is only common in public facing services". Good answer. Here's another link below that may be helpful in understanding the purpose of the namespace when used in Service Contract's that are public-facing - like online, public clients that access your service remotely.

  <https://stackoverflow.com/questions/3519014/wcf-versioning-update-attribute-namespaces-and-support-previous-namespaces?rq=1>

This link says the Service Contract attribute's namespace is necessary when public clients need to know which version of the "interface" is the new version - after the service has been updated or upgraded.

For public clients who want to use the newly updated interface, they would change their client proxy to use the new version of the Service - identified by the new "namespace". If they do not want or need to use the new version of the Service, they don't need to change anything in the client they currently use.

At least I think this is what the Service Contract attribute's namespace value would be used for. I don't use a namespace in my [ServiceContract] attribute because my User Interface, client proxies and Service Application are not "public-facing", but all are part of a Winforms desktop application solution - which accesses a remote database using Entity Framework and WCF Services (http SOAP).