Unicode Canonical Decomposition for Hangeul Syllables in Regular Expression

Owing to the high expressiveness of regular expression, it is frequently used in searching and manipulation of text based data. Regular expression is highly applicable in processing Latin alphabet based text, but the same cannot be said for Hangeul∗, the writing system for Korean language. Although Hangeul possesses alphabetic features within the script, expressiveness of regular expression pattern using Hangeul is hindered by the absence of syllable decomposition. Without decomposition support in regular expression, searching through Hangeul text is limited to string literal matching. Literal matching has made enumeration of syllable candidates in regular expression pattern definition indispensable, albeit impractical, especially for a large set of syllable candidates. Although the existing implementation of canonical decomposition in Unicode standard does reduce a pre-composed Hangeul syllable into smaller unit of consonantvowel or consonant-vowel-consonant letters, it still leaves quite a number of the individual letters in compounded form. We have observed that there is a necessity to further reduce the compounded letters into unit of basic letters to properly represent the Korean script in regular expression. We look at how the new canonical decomposition technique proposed by Kim can help in handling Hangeul in regular expression. In this paper, we examine several of the performance indicators of full decomposition of Hangeul syllable to better understand the overhead that might incur, if a full decomposition were to be implemented in a regular expression engine. For efficiency considerations, we propose a semi decomposition technique alongside with a notation for defining Hangeul syllables. The semi decomposition functions as an enhancement to the existing regular expression syntax by taking in some of the special constructs and features of the Korean language. This proposed technique intends to allow an end user to have a greater freedom to define regular expression syntax for Hangeul. key words: regular expression, Hangeul, Unicode, NFD, Korean script