WSDL to have attributes instead of nodes

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C#

WCF

Hi

i have created a simple web method("Open") and the SOAP is looking like below

<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
  <s:Header>
    <Action s:mustUnderstand="1" xmlns="http://schemas.microsoft.com/ws/2005/05/addressing/none">urn:IEhelplineService/Open</Action>
  </s:Header>
  <s:Body>
    <Open>
      <attachment>
        <name>c:1.jpg</name>
        <type>jpg</type>
        <encodedstring>fdsfdsfdsf3434324$#@$#@$</encodedstring>
      </attachment>
    </Open>
  </s:Body>
</s:Envelope>

Open is the web method with operationcontract attribute and attachment is its parameter. Attachment is the class with datacontract attribute. Currently name,type and encodedstring are parameters with datamember attributes.

I want it to look like below.

<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
  <s:Header>
    <Action s:mustUnderstand="1" xmlns="http://schemas.microsoft.com/ws/2005/05/addressing/none">urn:IEhelplineService/Open</Action>
  </s:Header>
  <s:Body>
    <Open>
      <attachment name="c:1.jpg" type="jpg">fdsfdsfdsf3434324$#@$#@$</attachment>
    </Open>
  </s:Body>
</s:Envelope>

Difference is the name,type and encoded strings are attribute nodes in the xml than childnodes. how do i do it?