The idea is to prepare chaining process in XML server side.

Example :

<wps:Execute service="WPS" version="1.0.0"
  xsi:schemaLocation="http://www.opengis.net/wps/1.0.0 ../wpsExecute_request.xsd">
  <ows:Identifier>KMLgenerator</ows:identifier>
  <wps:DataInputs>
    <wps:Input>
      <ows:Identifier>Features</ows:identifier>
      <ows:Title>The Features</ows:title>
      <ows:Reference xlink:href="projection"
        method="POST" mimeType="text/xml" encoding="UTF-8">
        <wps:Body>
<wps:Execute service="WPS" version="1.0.0"
  xsi:schemaLocation="http://www.opengis.net/wps/1.0.0 ../wpsExecute_request.xsd">
  <ows:Identifier>KMLgenerator</ows:identifier>
  <wps:DataInputs>
    <wps:Input>
      <ows:Identifier>InputSRS</ows:identifier>
      <ows:Title>The input SRS</ows:title>
      $[SRS]
    </wps:input>
    <wps:Input>
      <ows:Identifier>InputFeatures</ows:identifer>
      <ows:Title>The input feature</ows:title>
      $[Features]
    </wps:input>
    <wps:Input>
      <ows:Identifier>OutputSRS</ows:identifier>
      <ows:Title>The output SRS</ows:title>
      <wps:Data>
        <wps:LiteralData>EPSG:4326</wps:literaldata>
      </wps:data>
    </wps:input>
  </wps:datainputs>
</wps:execute>
        </wps:body>
      </ows:reference>
    </wps:input>
  </wps:datainputs>
  <wps:ResponseForm>
    <wps:RawDataOutput>
      <ows:Identifier>KML</ows:identifier>
    </wps:rawdataoutput>
  </wps:responseform>
</wps:execute>

This example is a process to generate KML