Encyclopedia of Computer Science and Technology

Dreyfus, Hubert 161gle computer) to a more comprehensive “network objectmodel.”Document and object models are also increasinglyimportant for working on the Web. This can be seen inthe increasing use of XML documents and the DocumentObject Model (see xml and dom). This involves the use of aconsistent programming interface (see api) by which manyapplications can create or process XML documents for datacommunication or display.Further ReadingBornestein, Niel M. .NET and XML. Sebastapol, Calif.: O’ReillyMedia, 2003.“Document Object Model (DOM).” World Wide Web Consortium.Available online. URL: http://www.w3.org/DOM/. AccessedAugust 12, 2007.Lowry, Juval. Programming .NET Components. 2nd ed. Sebastapol,Calif.: O’Reilly Media, 2005.“Open Document Format for Office Applications: OASIS Standard.”Available online. URL: http://docs.oasis-open.org/office/v1.0. Accessed July 10, 2007.DOM (Document Object Model)The Document Object Model (DOM) is a way to representa Web document (see html and xml) as an object thatcan be manipulated using code in a scripting language (seeJavaScript). The DOM was created by the World Wide WebConsortium (W3C) as a way to standardize methods ofmanipulating Web pages at a time when different browsersused different access models. The full specification isdivided into four levels (0 through 3). By 2005, most DOMspecifications were supported by the major Web browsers.Using DOM, a programmer can navigate through thehierarchical structure of a document, following links or“descending” into forms and user-interface objects. WithDOM one can also add HTML or XML elements, as well asload, save, or format documents.Code can also be written to respond to a number of“events,” including user keyboard or mouse activity andinteractions with specific user-interface elements andHTML forms. For example, the “mouseover” event will betriggered when the user moves the mouse cursor over adefined region. The code can then perform an action suchas popping up a box with explanatory text. The “submit”event will be triggered when the user has finished fillingin a form and clicked the button to send it to the Website. When an event occurs, the event object is used topass detailed information about it to the program, such aswhich key or button was pressed, the location of the mousepointer, and so on.Although learning the DOM methods and how to usethem takes some time, and familiarity with JavaScript ishelpful, the syntax for accessing DOM methods should befamiliar to anyone who has used an object-oriented programminglanguage. Here are some simple sample statements.Get the document with the specified ID:document.getElementById(ID)Get the element with the specified tag:document.getElementByTagName(tagname)Get the specified attribute (property) ofthe specified element:myElement.getAttribute(attributeName)Create an element with the specified tag andreference it through a variable:var myElementNode = document.createElement(tagname)EvaluationAlthough dynamic HTML (DHTML) also has an objectmodel that can be used to access and manipulate individualelements, DOM is more comprehensive because it providesaccess to the document as a whole and the ability to navigatethrough its structure.By providing a uniform way to manipulate documents,DOM makes it easier to write tools to process them in aseries of steps. For example, database programs and XMLparsers can produce DOM document “trees” as output, andan XSLT (XML style sheet processor) can then be used toformat the final output.For working with XML, another popular alternative isthe Simple API for XML (SAX). The SAX model is quite differentfrom DOM in that the former “sees” a document asa stream of events (such as element nodes) and the parseris programmed to call methods as events are encountered.DOM, on the other hand, is not a stream but a tree that canbe entered arbitrarily and traversed in any direction. Onthe other hand, SAX streams do not require that the entiredocument be held in memory, and processing can sometimesbe faster.Further ReadingDocument Object Model FAQ. World Wide Web Consortium.Available online. URL: http://www.w3.org/DOM/faq.html.Accessed September 16, 2007.Heilmann, Christian. Beginning JavaScript with DOM Scripting andAjax: From Novice to Professional. Berkeley, Calif.: APress, 2006.Keith, Jeremy. DOM Scripting: Web Design with JavaScript and theDocument Object Model. Berkeley, Calif.: APress, 2005.Robie, Jonathan. “What Is the Document Object Model?” WorldWide Web Consortium. Available online. URL: http://www.w3.org/TR/WD-DOM/introduction.html. Accessed September14, 2007.Sambells, Jeffrey, and Aaron Gustafson. Advanced DOM Scripting:Dynamic Web Design Techniques. Berkeley, Calif.: APress,2007.DOS See ms-dos.Dreyfus, Hubert(1929– )AmericanPhilosopher, Cognitive PsychologistAs the possibilities for computers going beyond “numbercrunching” to sophisticated information processing becameclear starting in the 1950s, the quest to achieve artificial intelligence(AI) was eagerly embraced by a number of innovative