Config Cronjob Definition

<config>
    <crontab>
        <jobs>
            <cron_job_name>
                <schedule>
                    <cron_expr>* * * * *</cron_expr>
                </schedule>                
                <run>
                    <model>your_module/model::batchTransactions</model>
                </run>
            </cron_job_name>
        </jobs>
    </crontab>
</config>