Encyclopedia of Computer Science and Technology

84 chess and computersOne of the best known and most versatile modern chatterbotsis ALICE (Artificial Linguistic Internet Computer Entity),developed by Richard Wallace. ALICE does much more thansimply echo statements; it includes an elaborate parser andsentence generator and specialized scripts for initiating orresponding to conversational gambits. ALICE can even telllies and spread “gossip” that it learns from other users.In the following dialog ALICE seems to be able torespond appropriately:Human: Are you intelligent?ALICE: I am highly intelligent. I have many intellectual functions.Human: How do you know you are intelligent?ALICE: By introspection.However the illusion breaks down as the matter ispressed further and the bot uses a “deflection” strategy:Human: What were you thinking while you said that?ALICE: I was minding my own business.Human: How do you feel about being interrogated in this way?ALICE: The opposite of not being interrogated in this way.Still, with more than 25,000 conversation templatesstored in XML files that are modifiable by the user, ALICEhas repeatedly won the Loebner Contest, a modern versionof the Turing test.Although many are created as programming exercisesor for amusement, chatterbots embody principles that areimportant in artificial intelligence research, including naturallanguage processing and machine learning (see artificialintelligence). Techniques first developed withchatterbots can contribute to the creation of programsdesigned to provide answers to users’ questions or otherforms of assistance (see software agent).moves for the computer chess player, the possible repliesof the opponent to each move, the possible next moves bythe computer, and so on for as many half moves or “plies”as possible. The moves would be evaluated by a “minimax”algorithm that would find the move that best improves thecomputer’s position despite the opponent’s best play.The fundamental problem with the brute force is the“combinatorial explosion”: Looking ahead just three moves(six plies) would involve evaluating more than 700,000,000positions. This was impractical given the limited computingpower available in the 1950s. Shannon realized thisand decided that a successful chess program would have toincorporate principles of chess strategy that would enable itto quickly recognize and discard moves that did not showa likelihood of gaining material or improving the position(such as by increasing control of center squares). As a resultof this “pruning” approach, only the more promising initialmoves would result in the program looking ahead—butthose moves could be analyzed much more deeply.The challenge of the pruning approach is the need toidentify the principles of good play and codify them in sucha way that the program can use them reliably. Progresswas slow at first—programs of the 1950s and 1960s couldscarcely challenge an experienced amateur human player,let alone a master. A typical program would play a mixtureof reasonable moves, odd-looking but justifiable moves,and moves that showed the chess version of “nearsightedness.”By the 1970s, however, computing power was rapidlyincreasing, and a new generation of programs such as Chess4.0 from Northwestern University abandoned most pruningtechniques in favor of brute-force searches that could nowextend further ahead. In practice, each programmer chose aparticular balance between brute force and pruning-selectionFurther ReadingA.L.I.C.E. Artificial Intelligence Foundation. Available online.URL: http://www.alicebot.org/. Accessed April 27, 2007.Chatterbot Central (The Simon Laven Page). Available online.URL: http://www.simonlaven.com/. Accessed April 27, 2007.Loebner Prize. Available online. URL: http://www.loebner.net/Prizef/loebner-prize.html. Accessed April 27, 2007.chess and computersWith simple rules but endless permutations, chess has fascinatedmillions of players for hundreds of years. Whenmechanical automatons became fashionable in the 18thcentury, onlookers were intrigued by “the Turk,” a chessplayingautomaton. While the Turk was eventually shownto be a hoax (a human player was hidden inside), the developmentof the electronic digital computer in the mid-20thcentury provided the opportunity to create a true automaticchess player.In 1950 Claude Shannon outlined the two basic strategiesthat would be used by future chess-playing programs.The “brute force” strategy would examine the possibleIn the 18th century the Turk, a mechanical chess player, astonishedonlookers. Although the original Turk was a fraud (a small humanplayer was hidden inside), the modern computer chess programFritz 9 pays its homage by simulating its predecessor. (Fritz 9,Chessbase GmbH, www.chessbase.com)