TraceListener with writing message to data base

DataBaseWriterTraseListiner.cs

/* Config setting
<configuration>
  <system.diagnostics>
    <sources>
      <source name="System.ServiceModel.MessageLogging">
        <listeners>
          <add name="xml" />
        </listeners>
      </source>
    </sources>
    <sharedListeners>
      <add name="xml"
           type="<Namespace>.DataBaseWriterTraseListiner, <Assembly name>, Version=1.0.0.0, Culture=neutral, PublicKeyToken=<Token key | null>"
                 initializeData="DB" />
    </sharedListeners>
  </system.diagnostics>
  <system.serviceModel>
    <diagnostics wmiProviderEnabled="true">
    <endToEndTracing propagateActivity="true" />
      <messageLogging
           logEntireMessage="true"
           logMalformedMessages="false"
           logMessagesAtServiceLevel="false"
           logMessagesAtTransportLevel="true"
         >
      </messageLogging>
    </diagnostics>
  </system.serviceModel>
</configuration>
*/

public class DataBaseWriterTraseListiner : TraceListener
    {
        string action;
        Guid messageID             = Guid.Empty;
        const string REGEX_PATTERN = @"[.\w]+$";
        const string ENVELOP       = "Envelope";
        const string ACTION        = "Action";
        const string MESSAGEID     = "MessageID";

        public DataBaseWriterTraseListiner()
        {
        }

        public DataBaseWriterTraseListiner(string name)
            : base(name)
        {
            if(name != "DB")
                throw new NotImplementedException("The saving trace message to file not implemented!");
        }

        public override void Write(string message)
        {
        }

        public override void WriteLine(string message)
        {
            string parseMessage = string.Empty;
            string actionAttribute = string.Empty;
            string source = string.Empty;

            XDocument xDoc = XDocument.Parse(message);

            List<XElement> docList = xDoc.Descendants().ToList<XElement>();

            if(docList.Exists(m => m.Name.LocalName == ENVELOP))
            {

                source = xDoc.Root.FirstAttribute.NextAttribute.Value;

                if(docList.Exists(m => m.Name.LocalName == ACTION))
                {
                    action = docList.SingleOrDefault(m => m.Name.LocalName == ACTION).Value;

                }

                if(Regex.IsMatch(action, REGEX_PATTERN))
                    actionAttribute = Regex.Match(action, REGEX_PATTERN, RegexOptions.IgnoreCase).Value;

                if(docList.Exists(m => m.Name.LocalName == MESSAGEID))
                {
                    if(!messageID.Equals(docList.SingleOrDefault(m => m.Name.LocalName == MESSAGEID).Value))
                    {
                        messageID = Guid.Parse(docList.SingleOrDefault(m => m.Name.LocalName == MESSAGEID).Value.Replace("urn:uuid:", string.Empty));
                    }
                }

              parseMessage = docList.Elements().Single(m => m.Name.LocalName == ENVELOP).ToString();

              WriteTraceToDB(source, actionAttribute, action, parseMessage);
            }
        }
    }