public function getLinkTypeColumnCallback($columnName)
    {

        // query whether or not a callback mapping is available
        if (isset($this->linkTypeAttributeColumnToCallbackMapping[$columnName])) {
            // load it from the array with the mappings
            list (, $callbackName) = $this->linkTypeAttributeColumnToCallbackMapping[$columnName];
            // prepare and return the callback
            return array($this, $callbackName);
        }

        // return the default callback
        return array($this, 'explode');
    }