Relations serve as the glue that forms concepts (like "Madonna" and "Singer") into statements (like "Madonna is a singer"). Relations are also used when connecting Cyc's knowledge to external knowledge sources, such as corporate databases and Web pages. Some relations connect statements to each other to form rules, such as "If a car was manufactured after 1995, then the car contains an air bag." Unlike other technologies that use a handful of relations, Cyc relies on an extensible set of thousands of relations. And Cyc's relations are themselves connected using relations, which provides (among other things) a kind of automatic learning. When you add the fact that an air bag is part of the safety subassembly of Car X, the KB automatically knows that Car X contains an air bag, that it contains all the parts that make up the air bag, that the air bag is inside Car X, etc. This happens as a result of the already established relationships connecting contains, parts and inside.