Dale - Computer Science Illuminated 93

Dale - Computer Science Illuminated 93 - Keyword Encoding...

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Keyword encoding Substituting a frequently used word with a single character 66 Chapter 3 Data Representation to the extended ASCII character set, including the codes used to represent them. Therefore, programs that assume ASCII values are unaffected even if the underlying system embraces the Unicode approach. Text Compression Alphabetic information (text) is a fundamental type of data. Therefore, it is important that we find ways to store text efficiently and transmit text efficiently between one computer and another. The following sections examine three types of text compression: ± keyword encoding ± run-length encoding ± Huffman encoding As we discuss later in this chapter, some of the underlying ideas of these text compression techniques come into play when dealing with other types of data as well.
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Unformatted text preview: Keyword Encoding Consider how often you use words such as “the,” “and,” “which,” “that,” and “what.” If these words took up less space (that is, had fewer charac-ters), our documents would shrink in size. Even though the savings on each word would be small, they are used so often in a typical document that the combined savings would add up quickly. One fairly straightforward method of text compression is called keyword encoding , in which frequently used words are replaced with a single character. To decompress the document, you reverse the process: replace the single characters with the appropriate full word. For example, suppose we used the following chart to encode a few words: Word Symbol as the and that must well those ^ ~ + $ & % #...
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This note was uploaded on 01/13/2011 for the course CSE 1550 taught by Professor Marianakant during the Fall '10 term at York University.

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