【正文】 y clients at once. Generally, a database management system is involved, so the designer “balances” the layout of data into tables for optimal use. In addition, systems often allow a client to insert new information into a server. This means you must ensure that one client’s new data doesn’t walk over another client’s new data, or that data isn’t lost in the process of adding it to the database (this is called transaction processing). As client software changes, it must be built, debugged, and installed on the client machines, which turns out to be more plicated and expensive than you might think. It’s especially problematic to support multiple types of puters and operating systems. Finally, there’s the allimportant performance issue: You might have hundreds of clients making requests of your server at any one time, so any small delay is crucial. To minimize latency, programmers work hard to offload processing tasks, often to the client machine, but sometimes to other machines at the server site, using socalled middleware. (Middleware is also used to improve maintainability.)The simple idea of distributing information has so many layers of plexity that the whole problem can seem hopelessly enigmatic. And yet it’s crucial: Client/server puting accounts for roughly half of all programming activities. It’s responsible for everything from taking orders and creditcard transactions to the distribution of any kind of data—stock market, scientific, government, you name it. What we’ve e up with in the past is individual solutions to individual problems, inventing a new solution each time. These were hard to create and hard to use, and the user had to learn a new interface for each one. The entire client/server problem needs to be solved in a big way.The Web as a giant serverThe Web is actually one giant client/server system. It’s a bit worse than that, since you have all the servers and clients coexisting on a single network at once. You don’t need to know that, because all you care about is connecting to and interacting with one server at a time (even though you might be hopping around the world in your search for the correct server).Initially it was a simple oneway process. You made a request of a server and it handed you a file, which your machine’s browser software (., the client) would interpret by formatting onto your local machine. But in short order people began wanting to do more than just deliver pages from a server. They wanted full client/server capability so that the client could feed information back to the server, for example, to do database lookups on the server, to add new information to the server, or to place an order (which required more security than the original systems offered). These are the changes we’ve been seeing in the development of the Web.The Web browser was a big step forward: the concept that one piece of information could be displayed on any type of puter without change. However, browsers were still rather primitive and rapidly bogged down by the demands placed on them. They weren’t particularly interactive, and tended to clog up both the server and the Internet because any time you needed to do something that required programming you had to send information back to the serv