public function getSpanSummary()
    {
        $summary = [];
        
        $span = $this->dbObject('Span');
        
        foreach ($span->getViewports() as $viewport) {
            
            if ($value = $span->getField($viewport)) {
                $summary[] = sprintf('%s: %s', $viewport, $value);
            }
            
        }
        
        return implode(', ', $summary);
    }