Chinese character description languages

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Several systems have been proposed for describing the internal structure of Chinese characters, including their strokes, components, and the stroke order, and the location of each in the character's ideal square. This information is useful for identifying variants of characters that are unified into one code point by Unicode and ISO/IEC 10646, as well as to provide an alternative form of representation for rare characters that do not yet have a standardized encoding in Unicode. Many aim to work for regular script, as well as to provide the character's internal structure which can be used for easier look-up of a character by indexing the character's internal make-up and cross-referencing among similar characters.

Contents

CDL

Character Description Language (CDL) is an XML-based declarative language co-created by Tom Bishop and Richard Cook for the Wenlin Institute. It defines characters by the arrangement of components, which are not required to reflect the semantic or etymological history of the character. In order for a component to fit into the allotted portion of the whole character's square, A set of fewer than 50 strokes allow one to construct approximately 1,000 components, which may in turn describe tens of thousands of characters. [1]

Ideographic Description Sequences

Chapter 18 of The Unicode Standard (version 15.0) defines the "Ideographic Description Sequences" (IDS) syntax used to describe characters in featural terms, by arrangements of components with code points. Sixteen special characters in the range U+2FF0..U+2FFF act as prefix operators to combine other characters or sequences to form larger characters.

Ideographic Description Characters in Unicode
CharacterUnicode Character NumberFull Unicode Name
U+2FF0Ideographic description characterleft to right
U+2FF1Ideographic description characterabove to below
U+2FF2Ideographic description characterleft to middle and right
U+2FF3Ideographic description characterabove to middle and below
U+2FF4Ideographic description characterfull surround
U+2FF5Ideographic description charactersurround from above
U+2FF6Ideographic description charactersurround from below
U+2FF7Ideographic description charactersurround from left
U+2FFCIdeographic description charactersurround from right
U+2FF8Ideographic description charactersurround from upper left
U+2FF9Ideographic description charactersurround from upper right
U+2FFAIdeographic description charactersurround from lower left
U+2FFDIdeographic description charactersurround from lower right
U+2FFBIdeographic description characteroverlaid
U+2FFEIdeographic description characterhorizontal reflection
⿿U+2FFFIdeographic description characterrotation

Two additional ideographic description characters are scattered in other Unicode blocks. U+303EIDEOGRAPHIC VARIATION INDICATOR is not officially an ideographic description character, but is sometimes used in ideographic description sequences.

Other Ideographic Description Characters in Unicode
CharacterCode pointBlockName
U+303E CJK Symbols and Punctuation Ideographic variation indicator
U+31EF CJK Strokes Ideographic description charactersubtraction

These sequences are useful in describing to the reader a character that is not directly printable, either because it is absent in a given font, or is absent from the Unicode standard altogether. For example, the sawndip character Saw sawndip.svg encoded in CJK Unified Ideographs Extension F as U+2DA21 𭨡 can be described as ⿰書史. Another use is for dictionary lookup purposes, as a rough input method for queries.

These sequences can be rendered either by keeping the individual characters separately or by parsing the Ideographic Description Sequence and drawing the ideograph so described. They do not, by themselves, provide unambiguous rendering for all characters. For instance, the sequence ⿱十一 represents both 'EARTH' with the middle bar being narrower, and 'SCHOLAR' with the middle bar being wider.

Unicode's specification for these sequences is based on the characters and syntax of the earlier GBK encoding. Additional symbols are later encoded to fill in the missing combinations.

The IDSgrep free software package by Matthew Skala [2] [3] extends Unicode's IDS syntax to include additional features for dictionary lookup; it is capable of converting KanjiVG's database to its own extended IDS format, or of searching EIDS files generated by the related Tsukurimashou font family.

See also

Related Research Articles

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The Chinese, Japanese and Korean (CJK) scripts share a common background, collectively known as CJK characters. During the process called Han unification, the common (shared) characters were identified and named CJK Unified Ideographs. As of Unicode 15.1, Unicode defines a total of 97,680 characters.

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CJK Unified Ideographs Extension-A is a Unicode block containing rare Han ideographs submitted to the Ideographic Research Group between 1992 and 1998, plus ten ideographs added in Unicode 13.0 which had previously been mistakenly unified with others.

Kangxi Radicals is a Unicode block. In version 3.0 (1999), this separate Kangxi Radicals block was introduced which encodes the 214 radicals in sequence, at U+2F00–2FD5. These are specific code points intended to represent the radical qua radical, as opposed to the character consisting of the unaugmented radical; thus, U+2F00 represents radical 1 while U+4E00 represents the character meaning "one". In addition, the CJK Radicals Supplement block (2E80–2EFF) was introduced, encoding alternative forms taken by Kangxi radicals as they appear within specific characters. For example, ⺁ "CJK RADICAL CLIFF" (U+2E81) is a variant of ⼚ radical 27 (U+2F1A), itself identical in shape to the character consisting of unaugmented radical 27, 厂 "cliff" (U+5382).

A variant form is an alternate glyph for a character, encoded in Unicode through the mechanism of variation sequences: sequences in Unicode that consist of a base character followed by a variation selector character.

CJK Unified Ideographs Extension B is a Unicode block containing rare and historic CJK ideographs for Chinese, Japanese, Korean, and Vietnamese submitted to the Ideographic Research Group between 1998 and 2000, plus seven gongche characters for kunqu added in Unicode 13.0, and two characters for the Macao Supplementary Character Set added in Unicode 14.0.

CJK Unified Ideographs Extension C is a Unicode block containing rare and historic CJK ideographs for Chinese, Japanese, Korean, and Vietnamese submitted to the Ideographic Research Group between 2002 and 2006, plus five "urgently needed" characters added in Unicode versions 14.0 and 15.0, some of which had previously been mistakenly unified with other characters.

CJK Unified Ideographs Extension D is a Unicode block containing uncommon CJK ideographs for Chinese, Japanese, Korean, and Vietnamese, some of which are in current use. Much smaller than most Unicode blocks for CJK unified ideographs, Extension D consists of characters which were submitted to the Ideographic Research Group as "urgently needed characters" between 2006 and 2009. Characters submitted during the same period which were needed less urgently were included in CJK Unified Ideographs Extension E instead.

CJK Compatibility Ideographs is a Unicode block created to contain mostly Han characters that were encoded in multiple locations in other established character encodings, in addition to their CJK Unified Ideographs assignments, in order to retain round-trip compatibility between Unicode and those encodings. However, it also contains 12 unified ideographs sourced from Japanese character sets from IBM.

Ideographic Description Characters is a Unicode block containing graphic characters used for describing CJK ideographs. They are used in Ideographic Description Sequences (IDS) to provide a description of an ideograph, in terms of what other ideographs make it up and how they are laid out relative to one another. An IDS provides the reader with a description of an ideograph that cannot be represented properly, usually because it is not encoded in Unicode; rendering systems are not intended to automatically compose the pieces into a complete ideograph, and the descriptions are not standardized.

CJK Unified Ideographs Extension E is a Unicode block containing rare and historic CJK ideographs for Chinese, Japanese, Korean, and Vietnamese submitted to the Ideographic Research Group between 2006 and 2013, excluding the characters submitted as "urgently needed" between 2006 and 2009, which were included in CJK Unified Ideographs Extension D.

CJK Unified Ideographs Extension F is a Unicode block containing rare and historic CJK ideographs for Chinese, Japanese, Korean, and Vietnamese, as well as more than a thousand Sawndip characters for writing the Zhuang language, which were submitted to the Ideographic Research Group between 2012 and 2015.

References

Citations

  1. Bishop & Cook (2003c), pp. 2, 9.
  2. "IDSgrep", Tsukurimashou Project, 2024, archived from the original on Feb 7, 2024
  3. Skala, Matthew (2015), "A Structural Query System for Han Characters" (PDF), International Journal of Asian Language Processing, vol. 23, no. 2, pp. 127–159, arXiv: 1404.5585 , archived from the original (PDF) on 2016-03-04, retrieved 2016-01-13

Works cited