Encyclopedia of Computer Science and Technology

DdataToday the term data is associated in many peoples’ mindsmainly with computers. However, data (as in “given facts”or measurements) has been used as a term by scientists andscholars for centuries. Just as with a counting bead, a notchin a stick, or a handwritten tally, data as stored in a computer(or on digital media) is a representation of facts aboutthe world. These facts might be temperature readings, customeraddresses, dots in an image, the characteristics ofa sound at a given instant, or any number of other things.But because computer data is not a fact but a representationof facts, its accuracy and usefulness depends not only onthe accuracy of the original data, but on its context in thecomputer.At bottom, computer data consists of binary states (representednumerically as ones or zeroes) stored using somephysical characteristic such as an electrical or magneticcharge or a spot capable of absorbing or reflecting light.A string of ones and zeroes in a computer has no inherentmeaning. Is the bit pattern 01000001 a number equivalentto 65 in the decimal system? Yes. Is it the capital letter “A”?It may be, if interpreted as an ASCII character code. Is itpart of some larger number? Again, it may be, if the memorylocation containing this pattern is interpreted as part ofa set of two, four, or more memory locations.In order to be interpreted, data must be assigned a categorysuch as integer, floating point (decimal), or character(see data types). The programming language compiler usesthe data type to determine how many memory locationsmake up that data item, and which bits in memory correspondto which bits in the actual number. Data items can betreated as a batch (see array) for convenience, or differentkinds of data such as names, addresses, and Social Securitynumbers can be grouped together into records or structuresthat correspond to an entity of interest (such as a customer).In creating a structure within the program to represent thedata, the programmer must be cognizant of its purpose andintended use.The programming language and code statements definethe context of data within the rules of the language. However,the meaning of data must ultimately be constructedby the human beings who use it. For example, whether atest score is good, bad, or indifferent is not a characteristicof the data itself, but is determined by the purposes ofthe test designer. This is why a distinction is often madebetween data, as raw numbers or characters, and informationas data that has been placed in a meaningful contextso that it can be useful and perhaps even enlightening tothe user.Further ReadingBierman, Alan W. Great Ideas in Computer Science: a Gentle Introduction.2nd ed. Cambridge, Mass.: MIT Press, 1997.Hillis, Daniel W. The Pattern on the Stone: the Simple Ideas thatMake Computers Work. New York: Basic Books, 1998.data abstractionAbstract data types are used to describe a “generic” type ofdata, specifying how the data is stored and what operationscan be performed on it (see object-oriented programming,list processing, stack, and queue).128