delete relational data MYSQL

In php and mysql and dmx, how would one modify the dmx delete record(or create ones own script) to delete from 2 tables containing "relationships" data? EXAMPLE a table called Books with Author ID's a table called Authors with ID's how could I delete all the Author's books from the Books table at the same time I delete that Author out of the Authors table(the Author id would be passed in the URL as "AID")? Any ideas or tutorials? -- Tim Haskins