namespace Test.ServiceModel
open System
open System.IO
open System.Collections
open System.Collections.Generic
open System.Runtime.Serialization
open ServiceStack
open ServiceStack.DataAnnotations
    [<AllowNullLiteral>]
    type HelloBase() = 
        member val Id:Int32 = new Int32() with get,set
    [<AllowNullLiteral>]
    type HelloWithInheritance() = 
        inherit HelloBase()
        member val Name:String = null with get,set
    [<AllowNullLiteral>]
    type HelloResponseBase() = 
        member val RefId:Int32 = new Int32() with get,set
    [<AllowNullLiteral>]
    type HelloWithInheritanceResponse() = 
        inherit HelloResponseBase()
        member val Result:String = null with get,set
To override the Content-type in your clients, use the HTTP Accept Header, append the .xml suffix or ?format=xml
The following are sample HTTP requests and responses. The placeholders shown need to be replaced with actual values.
POST /xml/reply/HelloWithInheritance HTTP/1.1 
Host: test.servicestack.net 
Accept: application/xml
Content-Type: application/xml
Content-Length: length
<HelloWithInheritance xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.datacontract.org/2004/07/Test.ServiceModel">
  <Id xmlns="http://schemas.datacontract.org/2004/07/Test.ServiceModel.Types">0</Id>
  <Name>String</Name>
</HelloWithInheritance>
HTTP/1.1 200 OK Content-Type: application/xml Content-Length: length <HelloWithInheritanceResponse xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.datacontract.org/2004/07/Test.ServiceModel"> <RefId xmlns="http://schemas.datacontract.org/2004/07/Test.ServiceModel.Types">0</RefId> <Result>String</Result> </HelloWithInheritanceResponse>