Compression Using Context Free Grammers

Matej Mežik (2011) Compression Using Context Free Grammers. EngD thesis.

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Abstract

The emergence of computers and their operating systems caused the transmition and storing huge amounts of data, which operating system can manage. We are limited with memory space and also with the transfer data time. This was the reason for invention of first algorithms for compression data to small packages, intended for the storage and transmission. Such packages can be later extended in the source data, which means that they are intended to lower consumption of available resources, either space or time. The main theme is the comparison of a handful of existing compression algorithms based on context-free grammar. It will identify one of them in selected file formats behave optimally. For comparison I took a basic version of the LZW algorithm, the Re-Pair algorithm and the bisection algorithm. All algorithms are used for core compression context-free grammar and dictionary. I also implemented algorithms in the Pascal programming language, with Delphi development environment and made the user interface for testing. I chose to compare the time (speed) and compression ratio between the source and the compressed file. The main purpose was to determine behavior of algorithms on the selected files of different formats: graphic BMP (bitmap) format, TXT format, PostScript format, and Java source.

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