class MyDataContractResolver : DataContractResolver
{
    private Dictionary<string, XmlDictionaryString> dictionary = new Dictionary<string, XmlDictionaryString>();
    Assembly assembly;

    // Definition of the DataContractResolver
    public MyDataContractResolver(Assembly assembly)
    {
        this.assembly = assembly;
    }

    // Used at deserialization
    // Allows users to map xsi:type name to any Type 
    public override Type ResolveName(string typeName, string typeNamespace, Type declaredType, DataContractResolver knownTypeResolver)
    {
        XmlDictionaryString tName;
        XmlDictionaryString tNamespace;
        if (dictionary.TryGetValue(typeName, out tName) && dictionary.TryGetValue(typeNamespace, out tNamespace))
        {
            return this.assembly.GetType(tNamespace.Value + "." + tName.Value);
        }
        else
        {
            return null;
        }
    }
    // Used at serialization
    // Maps any Type to a new xsi:type representation
    public override bool TryResolveType(Type type, Type declaredType, DataContractResolver knownTypeResolver, out XmlDictionaryString typeName, out XmlDictionaryString typeNamespace)
    {
        string name = type.Name;
        string namesp = type.Namespace;
        typeName = new XmlDictionaryString(XmlDictionary.Empty, name, 0); 
        typeNamespace = new XmlDictionaryString(XmlDictionary.Empty, namesp, 0);
        if (!dictionary.ContainsKey(type.Name))
        {
            dictionary.Add(name, typeName);
        }
        if (!dictionary.ContainsKey(type.Namespace))
        {
            dictionary.Add(namesp, typeNamespace);
        }
        return true;
    }
}