URLs, and links. And, more precisely, an URL is the only way to refer to a resource. There may be multiple URLs pointing to the same. Aside what appared to be

URLs, and links. And, more precisely, an URL is the only way to refer to a resource. There may be multiple URLs pointing to the same. Aside what appared to be a fundamental misunderstanding on the GP's part, there is the legitimate concern that an individual resource shouldn't need to know its own URL. In the article, that was just glossed over, though. One could, for example, have a book by ID 1 trickle the ID up the application call path, and at a higher level, a complete URL is generated. In fact, the application could simply be a module inside yet another one that wants to add its own ‘namespace’. What the URL is and how it's generated doesn't matter. All that does is that the URL is made available (discoverable), and that it goes to the right resource, however that happens.