Overloaded Web Methods – for "silo" apps only

Three years ago I did a presentation at Vermont.NET on Architecting Applications with Web Services. (Proof is at the past events page – check Feb 2003!) 

I clearly remember the question of overloaded web methods coming up in that session. I didn’t know the answer so I tried it right then and there and it didn’t work. Someone mentioned there was a way to get around it and we found that solution another day.

It’s still a question for a lot of people who are coming to Web Services as OO programmers (which Visual Studio lets us do) and that is because many are unfamiliar with the attributes that can be used for web services. Or they see them but have no idea what they are there for.

Thom Robbins recently had someone ask the same question and blogged how to use attributes to enable overloading when defining web methods in Visual Studio.NET.

Three years ago, it seemed like a good idea to me. I didn’t really grokWeb Services. I was just using them as a means to an end and I knew OO programming, not messaging.

However, now my perception has changed and it’s important to note (as Thom does (thanks Thom!)) that just because you can do it, doesn’t mean it’s a good thing. It’s the OO way, for sure, but it just does not jibe with messaging and contracts and it does not conform to WSI Basic profile which demands unique names for operations (web methods). So if you have any intentions of going outside of .NET with your messaging, don’t do it. A contract needs to be clearly defined and by providing overloads, that just blows the contract away.

If you are writing what the plumbers call "silo" apps, .NET all the way through and you are controlling the client and the service, there’s no harm outside of the damage you are doing to your brain. Still, it’s important for the WSDL that represents your web service identifies does not identify itself as conforming to WSI Basic profile. When you create a new web service in VS2005, by default, the service has attributes that claim to conform to the Basic Profile. Thom includes the caveat in there to set the services’ conformance claims to "none".

Here’s what a .Net web service class that shows what Conformance Claims  looks like. ConformsTo is the claim. Emit embeds the claim in the wsdl.


<WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1, EmitConformanceClaims:=True)> _
)> _
Public Class
  <WebMethod> _
  Public Function HelloWorld() As
  End Function
End Class

If you look at the wsdl (eg http:\\localhost\myservice.asmx?wsdl) you can see that claim. Here is the appropriate section of the wsdl.

<wsdl:binding name="ServiceSoap" type="tns:ServiceSoap">
  <wsi:Claim conformsTo="http://ws-i.org/profiles/basic/1.1" xmlns:wsi="http://ws-i.org/schemas/conformanceClaim/" />
  <soap:binding transport="http://schemas.xmlsoap.org/soap/http" />
<wsdl:operation name="HelloWorld">

When you explicitly define that the service does NOT conform, there is no claim in the WSDL that says "I do not conform". In that case, no claim is made at all.

So by marking your service with


even if you have EmitConformanceClaims set to true, there will be no wsi:Claim in the wsdl.

If you forget to remove the conformance claims, you will get a big fat error message when you try to call the asmx.

Service ‘Service’ does not conform to WS-I Basic Profile v1.1. Please examine each of the normative statement violations below.

and the detail tells you:

To make service conformant please make sure that all web methods belonging to the same binding have unique names.

The more you start understanding these things today, the more prepared you will be for WCF.

Don’t Forget: www.acehaid.org

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