public function toOntology() {
	    $inResources = array();
	    $outResources = is_null($this->outParameter)
	       ? array()
	       : $this->outParameter->toOntology();
	    foreach ($this->inParameters as $param) {
	        $inResources[] = $param->toOntology();
	    }
	    $serviceCallClass = $this->getClass( WfEngineOntology::CLASS_URI_CALL_OF_SERVICES);
	    $resource = $serviceCallClass->createInstanceWithProperties(array(
            OntologyRdfs::RDFS_LABEL => 'serviceCall',
			WfEngineOntology::PROPERTY_CALL_OF_SERVICES_SERVICE_DEFINITION    => $this->serviceDefinitionId,
			WfEngineOntology::PROPERTY_CALL_OF_SERVICES_ACTUAL_PARAMETER_IN    => $inResources,
			WfEngineOntology::PROPERTY_CALL_OF_SERVICES_ACTUAL_PARAMETER_OUT   => $outResources,
			WfEngineOntology::PROPERTY_CALL_OF_SERVICES_WIDTH                => '100',
			WfEngineOntology::PROPERTY_CALL_OF_SERVICES_HEIGHT               => '100'
        ));
	         
	    return $resource; 
	}