'Return a visualization data_source dictionary parsed from the given
XML element.'

def parse(self, xml_tree):

    returned = {}
    model_class = self.parse_model_class(xml_tree.find('model_class'))
    if (not model_class):
        raise ParsingException('data_source    needs    a    model    class')
    returned['model_class'] = model_class
    returned['tests'] = self.parse_tests(xml_tree.findall('test'))
    returned['to_params'] = {}
    to_params = self.parse_to_params(xml_tree.findall('to_param'))
    if to_params:
        returned['to_params'] = to_params
    return returned
