This week's giveaway is in the EJB and other Java EE Technologies forum. We're giving away four copies of EJB 3 in Action and have Debu Panda, Reza Rahman, Ryan Cuprak, and Michael Remijan on-line! See this thread for details.
About your first question, HFSJ is right. There must be at least one url-pattern. You're looking at the wrong place. You should be looking at the Servlets Specification. The DTD is not used anymore, you should check the Xml Schema instead. Download the servlets specification and check the "Deployment Descriptor Diagram".