Han unification is an effort by the authors of Unicode and the Universal Character Set to map multiple character sets of the Han characters of the so-called CJK languages into a single set of unified characters. Han characters are a feature shared in common by written Chinese (hanzi), Japanese (kanji), Korean (hanja) and Vietnamese (chữ Hán). Modern Chinese, Japanese and Korean typefaces typically use regional or historical variants of a given Han character. In the formulation of Unicode, an attempt was made to unify these variants by considering them as allographs – different glyphs representing the same "grapheme" or orthographic unit – hence, "Han unification", with the resulting character repertoire sometimes contracted to Unihan. Nevertheless, many characters have regional variants assigned to different code points, such as Traditional 個 (U+500B) versus Simplified 个 (U+4E2A).
Rationale and controversy
The Unicode Standard details the principles of Han unification. The Ideographic Research Group (IRG), made up of experts from the Chinese-speaking countries, North and South Korea, Japan, Vietnam, and other countries, is responsible for the process. One rationale was the desire to limit the size of the full Unicode character set, where CJK characters as represented by discrete ideograms may approach or exceed 100,000 characters. Version 1 of Unicode was designed to fit into 16 bits and only 20,940 characters (32%) out of the possible 65,536 were reserved for these CJK Unified Ideographs. Unicode was later extended to 21 bits allowing many more CJK characters (101,996 are assigned, with room for more). An article hosted by IBM attempts to illustrate part of the motivation for Han unification:
The problem stems from the fact that Unicode encodes characters rather than "glyphs," which are the visual representations of the characters. There are four basic traditions for East Asian character shapes: traditional Chinese, simplified Chinese, Japanese, and Korean. While the Han root character may be the same for CJK languages, the glyphs in common use for the same characters may not be. For example, the traditional Chinese glyph for "grass" uses four strokes for the "grass" radical [⺿], whereas the simplified Chinese, Japanese, and Korean glyphs [⺾] use three. But there is only one Unicode point for the grass character (U+8349) [草] regardless of writing system. Another example is the ideograph for "one," which is different in Chinese, Japanese, and Korean. Many people think that the three versions should be encoded differently. In fact, the three ideographs for "one" (一, 壹, or 壱) are encoded separately in Unicode, as they are not considered national variants. The first is the common form in all three countries, while the second and third are used on financial instruments to prevent tampering (they may be considered variants). Han unification has also caused considerable controversy, particularly among the Japanese public, who, with the nation's literati, have a history of protesting the culling of historically and culturally significant variants. (See Kanji § Orthographic reform and lists of kanji. Today, the list of characters officially recognized for use in proper names continues to expand at a modest pace.) In 1993, the Japan Electronic Industries Development Association (JEIDA) published a pamphlet titled "未来の文字コード体系に私達は不安をもっています｡" (We are worried for the future character encoding system JPNO 20985671), summarizing major criticism against the Han Unification approach adopted by Unicode.
Graphemes versus glyphs
A grapheme is the smallest abstract unit of meaning in a writing system. Any grapheme has many possible glyph expressions, but all are recognized as the same grapheme by those with reading and writing knowledge of a particular writing system. Although Unicode typically assigns characters to code points to express the graphemes within a system of writing, the Unicode Standard (section 3.4 D7) cautions:
An abstract character does not necessarily correspond to what a user thinks of as a "character" and should not be confused with a grapheme.
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