Suppose you run a Web site that includes a banner<br /><br />advertisement service. You contract with companies<br /><br />that want their ads displayed when poeple visit<br /><br />the pages on your site. Each time a visitor hits<br /><br />one of your pages, you serve an ad embedded in the<br /><br />page that is sent to the visitor's browser and<br /><br />assess the company a small fee. To represent this<br /><br />information, you maintain three tables. One table,<br /><br />company, has columns for company name, number,<br /><br />address, and telephone number. Another table, ad<br /><br />lists ad numbers, the number for the company that<br /><br />owns the ad, and the amount you charge per hit.<br /><br />The third table, hit, logs each ad hit by number<br /><br />and the date on which the ad was<br /><br />served.