Chinese Character Code for Information Interchange

The Chinese Character Code for Information Interchange (Chinese: 中文資訊交換碼) or CCCII is a character set developed specifically to address the problem of interchange of Chinese information. It is used mostly by libraries because the code contains various properties considered to be desirable by libraries. Its 94 ISO 2022 planes are grouped into 16 layers of 6 planes each. Layer 2 contains Simplified Chinese characters, with their row and cell numbers being the same as the Traditional Chinese equivalent in layer 1. Layers 3 through 12 contain further variant forms, at row and cell numbers homologous to the first two layers. Layer 13 contains kana and Japanese kokuji, and layer 14 contains hangul.[1]

CCCII is a superset of ASCII designed to conform to ISO 2022. Each Chinese character is represented by a 3-byte code in which each byte is 7-bit. Thus, the maximum number of Chinese characters representable in CCCII is 94×94×94 = 830584. In practice the number of characters encodable by CCCII would be less than this number, because variant characters are encoded in related ISO 2022 planes under CCCII, so most of the code points would have to be reserved for variants.

The code is adopted as the character set for Library of Congress with the name East Asia Coded Character (EACC, ANSI/NISO Z39.64). However, some CCCII characters don't have EACC equivalent.[2]