Encyclopedia of Computer Science and Technology

390 PrologGiven the scope and pace of today’s business, scientific, andother projects, project management software is often a vitaltool. However, using too elaborate a project tracking systemfor a relatively small and well-defined project may diverttime and energy away from the work itself. Fortunately, awide variety of project management programs are available,ranging from full-fledged products such as MicrosoftProject or Primavera Project Planner to simpler sharewareor free products.Further ReadingMarmel, Elaine. Microsoft Office Project 2007 Bible. Indianapolis:Wiley, 2007.Muir, Nancy C. Microsoft Office Project 2007 for Dummies. Hoboken,N.J.: Wiley, 2007.Open Workbench: Open-Source Project Scheduling for Windows.Available online. URL: http://www.openworkbench.org/.Accessed August 17, 2007.“Project Management Software.” Wikipedia. Available online.URL: http://en.wikipedia.org/wiki/Project_management_software. Accessed August 17, 2007.PrologSince the 1950s, researchers have been intrigued by thepossibility of automating reasoning behavior, such as logicalinference (see artificial intelligence). A number ofdemonstration programs have been written to prove theoremsstarting from axioms or assumptions. In 1972, Frenchresearcher Alain Colmerauer and Robert Kowalski at EdinburghUniversity created a logic programming languagecalled Prolog (for Programmation en Logique) as a way ofmaking automated reasoning and knowledge representationmore generally available.A conventional procedural program begins by definingvarious data items, followed by a set of procedures formanipulating the data to achieve the desired result. A Prologprogram, on the other hand, begins with a set of facts(axioms) that are assumed to be true. (This is sometimescalled declarative programming.)For example, the fact that Joe is the father of Bill wouldbe written:Father (Joe, Bill).The programmer then defines logical rules that apply tothe facts. For example:father (X, Y) :- parent (X, Y), is male (X)grandfather (X, Y) :- father (X, Z), parent(Z, Y)Here the first assertion says that a person X is the fatherof Y if he is the parent of Y and is male. The second assertionsays that X is Y’s grandfather if he is the father of aperson Z who in turn is a parent of Y.When a program runs, it processes queries, or assertionswhose truth is to be proven. Using a process calledunification, the Prolog system looks for facts or rules thatapply to the query and attempts to create a logical chainleading to proving the query is true. If the chain breaks(because no matching fact or rule can be found), the system“backtracks” by looking for another matching fact or rulefrom which to attempt another chain.Prolog aroused considerable interest among artificialintelligence researchers who were hoping to create a powerfulalternative to conventional programming languages forautomating reasoning. This interest was further spurredby the Japanese Fifth Generation Computer Program of the1980s, which sought to create logical supercomputers andmade Prolog its language of choice. Although some suchmachines were built, the idea never really caught on. However,Borland International (makers of the highly successfulTurbo Pascal) released a Turbo Prolog that made thelanguage more accessible to students using PCs, although itused some nonstandard language extensions.Despite its commercial success being limited, Prologhas been used in a number of areas of artificial intelligenceresearch. Its rules-based structure is naturally suitedfor expert systems, knowledge bases, and natural languageprocessing (see expert systems and knowledge representation).It can also be used as a prototyping languagefor designing systems that would then be recoded in conventionallanguages for speed and efficiency.Further ReadingBratck, Ivan. Prolog Programming for Artificial Intelligence. 3rd ed.Reading, Mass.: Addison-Wesley, 2000.Clocksin, W. F., and C. S. Mellish. Programming in Prolog: Usingthe ISO Standard. 5th ed. New York: Springer, 2003.Fisher, J. R. “Prolog: Tutorial.” Available online. URL: http://www.csupomona.edu/~jrfisher/www/prolog_tutorial/contents.html. Accessed August 17, 2007.Sterling, Leon, and Ehud Shapiro. The Art of Prolog: Advanced ProgrammingTechniques. 2nd ed. Cambridge, Mass.: MIT Press,1994.SWI-Prolog [free Prolog for Windows, Linux, and Mac OS]. Availableonline. URL: http://www.swi-prolog.org/. AccessedAugust 17, 2007.pseudocodeBecause humans generally think on a higher (or moreabstract) level than that provided by even relatively highlevelprogramming languages such as BASIC or Pascal, itis sometimes suggested that programmers use some formof pseudocode to express how the program is intended towork. Pseudocode can be described as a language that ismore natural and readable than regular programming languages,but sufficiently structured to be unambiguous. Forexample, the following pseudocode describes how to calculatethe cost of wall-to-wall carpet for a room:Get room length (in feet)Get room widthMultiply length by width to get area (insquare feet)Get price of carpet per square footMultiply price/sq. foot by area to get totalcost.Pseudocode generally includes the basic control structuresused in programming languages (see branching