Encyclopedia of Computer Science and Technology

266 knowledge representationattended the Bronx High School of Science, home of manyof the nation’s top future engineers. However, when it cametime for college, the family had no money to pay for hishigher education, so he attended night courses at the CityCollege of New York while working as an electronics technicianand later as an engineer. Kleinrock graduated first inhis class in 1957 and earned a fully paid fellowship to theMassachusetts Institute of Technology.At MIT Kleinrock became interested in finding ways forcomputers and their users to communicate with each other.The idea of computer networking was in its infancy, but hesubmitted a proposal in 1959 for Ph.D. research in networkdesign.In 1961 Kleinrock published his first paper, “InformationFlow in Large Communication Nets.” Existing telephonesystems did what was called “circuit switching”: Toestablish a conversation, the caller’s line is connected to thereceiver’s, forming a circuit that existed for the durationof the call. This also meant that the circuit would not beavailable to anyone else, and that if something was wrongwith the connection there was no way to route around theproblem.Kleinrock’s basic idea was to set up data connectionsthat would be shared among many users as needed. Insteadof the whole call (or data transmission) being assigned to aparticular circuit, it would be broken up into packets thatcould be sent along whatever circuit was the most direct.If there was a problem, the packet could be resent on analternative route. This form of “packet switching” providedgreat flexibility as well as more efficient use of the availablecircuits. Kleinrock further elaborated his ideas in hisdissertation, for which he was awarded his Ph.D. in 1963.The following year MIT published his book CommunicationsNets, the first full treatment of the subject.Kleinrock joined the faculty at the University of California,Los Angeles. In 1968 the Defense Department’sAdvanced Research Projects Agency (ARPA) asked him todesign a packet-switched network that would be known asARPANET. The computers on the network would be connectedusing special devices called Interface Message Processors(IMPs). The overall project was under the guidanceand supervision of one of Kleinrock’s MIT office mates,Lawrence Roberts.On October 29, 1969, Kleinrock and his assistants sentthe first data packets between UCLA and Stanford overphone lines. Their message, the word “login,” was hardly asdramatic as Alexander Graham Bell’s “Watson, come here,I need you!” Nevertheless, a form of communication hadbeen created that in a few decades would change the worldas much as the telephone had done a century earlier.The idea of computer networking did not catch on immediately,however. Besides requiring a new way of thinkingabout the use of computers, many computer administratorswere concerned that their computers might be swampedwith users from other institutions, or that they might ultimatelylose control over the use of their machines. Kleinrockworked tirelessly to convince institutions to join thenascent network. By the end of 1969 there were just fourARPANET “nodes”: UCLA, the Stanford Research Institute,UC Santa Barbara, and the University of Utah. By the followingsummer, there were ten.During the 1970s Kleinrock trained many of theresearchers who would advance the technology of networking.While Kleinrock’s first network was not the Internet weknow today, it was an essential step in its development. Insuccessfully establishing communication using the packetswitchedARPANET, Kleinrock showed that such a networkwas practicable.By the early 1990s Kleinrock was looking toward a futurewhere most network connections were wireless and accessiblethrough a variety of computerlike devices such as handheld“palmtop” computers, cell phones, and others not yetimagined. In such a network the intelligence or capability isdistributed throughout, with devices communicating seamlesslyso the user no longer need be concerned about whatparticular gadget he or she is using. By the middle of the followingdecade, much of this vision had become reality.Although his name is not well known to the generalpublic, Kleinrock has won considerable recognition withinthe technical community. This includes Sweden’s L. M.Ericsson Prize (1982), the Marconi Award (1986), and theNational Academy of Engineering Charles Stark DraperPrize (2001).Further ReadingHafner, Katie, and Matthew Lyon. Where Wizards Stay Up Late: TheOrigins of the Internet. New York: Simon and Schuster, 1996.Kleinrock, Leonard. “Information Flow in Large CommunicationNets.” Available online. URL: http://www.lk.cs.ucla.edu/LK/Bib/REPORT/PhD/proposal.html. Accessed May 3, 2007.“Leonard Kleinrock’s Home Page.” Available online. URL: http://www.lk.cs.ucla.edu/. Accessed May 3, 2007.knowledge representationThe earliest concern of computer science was the representationof “raw” data such as numbers in programs (see datatypes). Such data can be used in calculations, and actionstaken based on tests of data values, using branching (IF) orlooping structures.However, facts are more than data. A fact is an assertion,for example about a relationship, as in “Joe is a son ofMike,” often expressed in a form such as son (Joe, Mike).Implications can also be defined as proceeding from facts,such asson (Joe, Mike) implies father (Mike, Joe) orson (Joe, Mike) and son (Mike, Phil) impliesgrandson (Joe, Phil)While it can be expressed in a variety of different formsof notation, this predicate calculus forms the basis formany automated reasoning systems that can operate on a“knowledge base” of assertions, prove the validity of a givenassertion, and even generate new conclusions based uponexisting knowledge (see also expert systems).An alternative form of knowledge representation usedin artificial intelligence programs is based on the idea offrames. A frame is a structure that lists various character-