'Return a list of the parameter_id\'s that are to be used when
calculating the resilience indicator'

@staticmethod
def vulnerability_pids():

    if (S3VulnerabilityModel.indicator_pids is None):
        db = current.db
        table = db.vulnerability_indicator
        rows = db((table.deleted == False)).select(table.parameter_id)
        S3VulnerabilityModel.indicator_pids = [i.parameter_id for i in rows]
    return S3VulnerabilityModel.indicator_pids
