src/DataService/DataService.php
public function useJson()
    {
        $serviceContext = $this->getServiceContext();
        $serviceContext->useJson();
        $this->updateServiceContextSettingsForOthers($serviceContext);
        return $this;
    }
public function useJson()
    {
        $serviceContext = $this->getServiceContext();
        $serviceContext->useJson();
        $this->updateServiceContextSettingsForOthers($serviceContext);
        return $this;
    }
PHP SDK currently only support XML for Object Serialization and Deserialization, except for Report Service

@return $this