data structure Way in which data are stored for efficient search and retrieval. The simplest data structure is the one-dimensional (linear) array, in which stored elements are numbered with consecutive integers and contents are accessed by these numbers. Data items stored nonconsecu- tively in memory may be linked by pointers (memory addresses stored with items to indicate where the “next” item or items in the structure are located). Many algorithms have been developed for sorting data efficiently; these apply to structures residing in main memory and also to structures that constitute information systems and databases.
data transmission Sending and receiving data via cables (e.g., tele¬ phone lines or fibre optics) or wireless relay systems. Because ordinary telephone circuits pass signals that fall within the frequency range of voice communication (about 300-3,500 hertz), the high frequencies associated with data transmission suffer a loss of amplitude and transmission speed. Data signals must therefore be translated into a format compatible with the signals used in telephone lines. Digital computers use a modem to transform outgoing digital electronic data; a similar system at the receiv¬ ing end translates the incoming signal back to the original electronic data. Specialized data-transmission links carry signals at frequencies higher than those used by the public telephone network. See also broadband tech¬ nology; cable modem; DSL; ISDN; fax; radio; teletype; T1 ; wireless commu¬ nications.
database Collection of data or information organized for rapid search and retrieval, especially by a computer. Databases are structured to facili¬ tate storage, retrieval, modification, and deletion of data in conjunction with various data-processing operations. A database consists of a file or set of files that can be broken down into records, each of which consists of one or more fields. Fields are the basic units of data storage. Users retrieve database information primarily through queries. Using keywords and sorting commands, users can rapidly search, rearrange, group, and select the field in many records to retrieve or create reports on particular aggregates of data according to the rules of the database management sys¬ tem being used.
database, relational See relational database
database management system (DBMS) System for quick search and retrieval of information from a database. The DBMS determines how data are stored and retrieved. It must address problems such as security, accuracy, consistency among different records, response time, and memory requirements. These issues are most significant for database systems on computer networks. Ever-higher processing speeds are required for effi¬ cient database management. Relational DBMSs, in which data are orga¬ nized into a series of tables (“relations”) that are easily reorganized for accessing data in different ways, are the most widely used today.
Date Line See International Date Line
date palm Tree (Phoenix dactylifera) of the palm family, found in the Canary Islands and northern Africa, the Middle East, Pakistan, India, and California. The trunk, strongly marked with the pruned stubs of old leaf bases, ends in a crown of long, graceful, shining, pinnate leaves. The fruit, called the date, is a usually oblong brown berry. Dates have long been an important food in desert regions, and are the source of syrup, alcohol, vin¬ egar, and a strong liquor. All parts of the tree yield products of economic value, being used variously for timber, furniture, basketry, fuel, rope, and packing material. The seeds are sometimes used as stock feed. The tree is grown as an ornamental along the Mediterranean shores of Europe. Its leaves are used for the celebration of Palm Sunday (among Christians) and the Feast of Tabernacles (among Jews). Date sugar, a product of India, is obtained from the sap of a closely related species, P. sylvestris.
dating In geology and archaeology, the process of determining an object’s or event’s place within a chronological scheme. Scientists may use either relative dating, in which items are sequenced on the basis of stratigraphic clues (see stratigraphy) or a presumed evolution in form or structure, or absolute dating, in which items are assigned a date indepen¬ dent of context. The latter type includes potassium-argon and carbon- 14 dating; both are based on the measurement of radioactive decay. The record of changes in polarity of the Earth’s magnetic field has provided a timescale for seafloor spreading and long-term marine sedimentation. Den¬ drochronology has proved useful in archaeology and climatology. See also FISSION-TRACK DATING; HELIUM DATING; LEAD-210 DATING; RUBIDIUM-STRONTIUM
dating; URANIUM-234-URANIUM-238 dating; uranium-thorium-lead dating.
Daubenton \do-ba n -'to n \, Louis-Jean-Marie (b. May 26, 1716, Montbard, Cote d’Or, Fr.—d. Jan. 1, 1800, Paris) French naturalist. A prolific scientist, he completed many zoological descriptions and dissec¬ tions and undertook productive studies in the comparative anatomy of recent and fossil animals, plant physiology, and mineralogy. He intro¬ duced Merino sheep to France.
Daubigny \do-ben-'ye\, Charles-Francois (b. Feb. 15, 1817, Paris, Fr.—d. Feb. 19, 1878, Paris) French landscape painter of the Barbizon school. He was trained by his father, also a painter. He began by paint¬ ing historical and religious works but soon turned to landscapes, painting rivers, beaches, and canals from a boat. His images were notable for their uncrowded composition and accurate depiction of natural light. One of the earliest proponents of painting directly from nature, he is considered the link between mid-19th-century naturalism and Impressionism.
Daudet \do-'de\, Alphonse (b. May 13, 1840, Nimes, France—d. Dec. 16, 1897, Paris) French short-story writer and novelist. Daudet wrote his first novel at age 14. Unable to finish his schooling after his parents lost all their money, he took a position in a duke’s household. He later joined the army but fled the terrors of the Paris Commune of 1871. His health was long undermined by poverty and by the venereal disease that eventually cost him his life. He is remembered for his humorous, senti¬ mental portrayals of the life and characters of southern France, inspired by his experiences at several social levels. His many works include the
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Daughters of the American Revolution ► David I 515
story collection Monday Tales (1873), the play L’Arlesienne (1872), the novels The Nabob (1877) and Sappho (1884), and several volumes of memoirs. His son, Leon Daudet (1867-1942), edited with Charles Mau- rras the reactionary review L’Action Frangaise and was a virulent sati¬ rist and polemicist on the subjects of medicine and psychology as well as public affairs.
Daughters of the American Revolution (DAR) U.S. patriotic society for direct descendants of soldiers or others who aided the cause of independence. It was organized in 1890 and chartered by Congress in 1895. Its historical division stresses the study of U.S. history and preservation of Americana. Its educational division provides scholarships and loans, helps support schools for underprivileged youth and for Americanization train¬ ing, sponsors prizes, and publishes manuals. Its patriotic division publishes the Daughters of the American Revolution Magazine and The National Defense News. It was long known for its conservatism; its refusal in 1939 to let the black singer Marian Anderson perform at Washington’s Consti¬ tution Hall led to her famous concert at the Lincoln Memorial.
Daumier \dom-'ya\, Honore (-Victorin) (b. Feb. 20/26, 1808, Marseille, Fr.—d. Feb. 11, 1879, Valmondois) French painter, sculptor, and caricaturist. He was bom into a family of artists. From age 13 he worked for a bailiff in a law court and later as a clerk in a bookstore, where he observed and analyzed the appearance and behaviour of people of different social classes. In 1829, after studying lithography, he began contributing cartoons and drawings satirizing 19th-century French poli¬ tics and society to periodicals and came to enjoy a wide reputation. He produced more than 4,000 lithographs and 4,000 illustrative drawings. His paintings, drawing upon literary themes and documenting contemporary life and manners, were executed in a vigorous, sketchy style; they were rarely exhibited, and he remained unknown as a painter. In sculpture he specialized in caricature heads and figures; some 15 small clay busts occupy an important place in the history of sculpture.