Encyclopedia of Computer Science and Technology

characters and strings 81of an HTML document. The script can perform additionalfunctions such as logging the user’s query for marketingpurposes.The complexity of Web features and the heavy load onservers have prompted a number of strategies for servingdynamic content more efficiently. Traditionally, each timea CGI request is passed to the URL for a script, the appropriatelanguage interpreter must be loaded and initialized.However, modern Web servers such as Apache have built-inmodules for commonly used scripting languages such asPHP, Perl, Python, and Ruby. This allows the Web serverto run the script directly without the overhead of starting anew interpreter process.A more fundamental shift in implementation is thedevelopment of methods to tie together DHTML and XMLwith a document model and scripting languages to allowfor dynamic changes in page content without having toreload the page (see Ajax).Note: the acronym CGI can also stand for “computergeneratedimagery” (see computer graphics).Further Reading“A Guide to HTML and CGI Scripts.” Available online. URL: http://snowwhite.it.brighton.ac.uk/~mas/mas/courses/html/html.html. Accessed May 30, 2007.Hamilton, Jacqueline D. CGI Programming 101. Houston, Tex.:CGI101.com, 2000. (First six chapters are available freeonline at URL: http://www.cgi101.com/book/.) AccessedAugust 12, 2007.“The Most Simple Intro to CGI.” Available online. URL: http://bignosebird.com/prcgi.shtml. Accessed August 12, 2007.characters and stringsWhile the attention of the first computer designers focusedmainly on numeric calculations, it was clear that much ofthe data that business people and others would want tomanipulate with the new machines would be textual innature. Billing records, for example, would have to includecustomer names and addresses, not just balance totals.The “natural” representation of data in a computer is asa series of two-state (binary) values, interpreted as binarynumbers. The solution for representing text (letters of thealphabet, punctuation marks, and other special symbols) isto assign a numeric value to each text symbol. The result isa character code, such as ASCII (American Standard Codefor Information Interchange), which is the scheme usedmost widely today. (Another system, EBCDIC (ExtendedBinary-Coded Decimal Interchange Code) was used duringthe heyday of IBM mainframes, but is seldom used today.)The seven-bit ASCII system is compact (using one byteof memory to store each character), and was quite suitablefor early microcomputers that required only the basicEnglish alphabet, punctuation, and a few control characters(such as carriage return). In an attempt to use charactersto provide simple graphics capabilities, an “extendedASCII” was developed for use on IBM-compatible PCs.This used eight bits, increasing the number of charactersavailable from 128 to 256. However, the use of bitmappedgraphics in Windows and other operating systemsmade this version of ASCII unnecessary. Instead, the ANSI(American National Standards Institute) eight-bit characterset used the additional character positions to store avariety of special symbols (such as fractions and the copyrightsymbol) and various accent marks used in Europeanlanguages.Table of 7-Bit ASCII Character CodesThe following are control (nonprinting) characters:0 Null (nothing)7 Bell (rings on an old teletype; beeps on most PCs)8 Backspace9 Tab10 Line feed (goes to next line without changing columnposition)13 Carriage return (positions to beginning of next line)26 End of file27 [Esc] (Escape key)The characters with codes from 32 to 127 produce printablecharacters.32 [space] 64 @ 96 `33 ! 65 A 97 a34 “ 66 B 98 b35 # 67 C 99 c36 $ 68 D 100 d37 % 69 E 101 e38 & 70 F 102 f39 ‘ 71 G 103 g40 ( 72 H 104 h41 ) 73 I 105 i42 * 74 J 106 j43 + 75 K 107 k44 ‘ 76 L 108 l45 - 77 M 109 m46 . 78 N 110 n47 / 79 O 111 o48 0 80 P 112 p49 1 81 Q 113 q50 2 82 R 114 r51 3 83 S 115 s52 4 84 T 116 t53 5 85 U 117 u54 6 86 V 118 v55 7 87 W 119 w56 8 88 X 120 x57 9 89 Y 121 y58 : 90 Z 122 z59 ; 91 [ 123 {60 < 92 \ 124 |61 = 93 ] 125 }62 > 94 ^ 126 ~63 ? 95 - 127 [delete]