L2/04-050

Ideograph Variation Selector and Variation Collection Identifier

1. Introduction

Though there is a clear distinction between a concept of character and a concept of glyphic representation, in natural language processing, depending on the field of operation, same text stream often requires different operational domains. Representative two domains are as follows:

Character/contents-based processing domain:

Search and Retrieval, sort, natural language processing, machine translation.

Appearance-based processing domain:

A person's name, a place name, a geographical dictionary, a biographical dictionary, historical/geographical description.

A different methodology applies to a different field, however, the appearance-based processing domain is often misunderstood as a simple font typeface issue within the character-based processing domain. The requirements in the appearance-based processing domain will not satisfactory be fulfilled by ordinary font typeface settings in higher level protocol and even worse, there still be a strong demand on the appearance-based processing domain for plain text. The Unicode Standard Variation Selectors is a great step toward the solution to the issues with appearance-based processing domain, however, the requirements in this domain with Han ideographs involve further enhancement of the Unicode standard due to the nature of diverse usage of variations as common practice.

1.1 Problems and Requirements in use of Variation Selector for Ideographs

There need be a single comprehensive and definitive variation set and base characters definition as the well maintained standard which all whom need to resolve the problems in appearance-based processing domain, including national bodies who use ideographs and include ideographs in their national standards as well as all different research and study purposes, if we have to go with single set of variations as currently defined in Unicode 4.0 standard.

On the other hand, huge comprehensive variation collection does not fit with the needs of whom only requires target specific smaller but efficient set of variations due to the cost of system and effectiveness, in both data processing and rendering, as too much is as bad as too little.

There had been several attempts in academic field and national standard field to address the issues of the appearance-based processing domain, and the study shows it is practically too costly to develop such comprehensive one-fits-all set, if not impossible to develop.

The studies show the fact that the taxonomy of ideograph variations are diverse due to its historical and geographical background. One taxonomy classified based on particular set of historical document may not necessarily suitable for the use with other historical document written in different geographic region and/or in different era.

Requirements vary depending on the parties needing own variations and often are conflicting among them.

1.3 Definition

Variation Collection

2. Ideograph Variation Selector for Registration

2.1 Ideograph variation selector

Ideograph variation selector, proposed to be allocated in plane 14, can also change the visual appearance of the preceding base character as variation selector does, however, sequences involving those characters are not defined in the file Standardized-Variants.txt in the Unicode Character Database. Instead, the meaning of such a variation sequence is defined by an outside agreement between producers and consumers, called a Ideograph variation registry.

2.2 Ideograph variation registry

The ideograph variation registry consists of two information.

                                                                               
        File 1 contents:
                Adobe;Glyph Collection A;http://www.adobe.com/...
                JustSystem;Glyph Collection N;http://www.justsystem.co.jp/...
                                                                               
        File 2 contains:
                U+4E00 U+IVS17;JustSystem
                U+4E00 U+IVS18;JustSystem
                U+4E00 U+IVS19;Adobe
                U+4E01 U+IVS17;Adobe

2.2 Ideograph variation Registration Authority

Registration Authority works as an arbitrator of name space management as well as the central directory to find out the registered Ideograph Variation Selectors.
The registration authority only guarantees that for any given Unicode Han character NNNN, there is only one registered sequence NNNN + IVSn. That is, uniqueness of the *sequence* is guaranteed.
The registration authority does not test or guarantee that two sequences S1 and S2 have distinct or distinguishable glyphs.

2.3 Ideograph Variation Registrant

To make sure that piles of "garbage" don't get registered, the registration authority first qualifies the submitters in some way. Once qualified, a submitter can submit any number of sequences. The work of identifying, cataloging, and sequencing is done by the registrant, not by the registration authority. The registration authority just checks to see that the sequences are unique.
The registrant is strongly recomended to maintain pictures of variation in some form they register and any relevant reference information so that the variations they register can be identified by whom interested in.

2.4 Registration Methods

Ideograph Variation Registrant can choose the method of registration from two ways.

 general category Mn
 canonical combining class 0 
 bidirectional category NSM 
 no decomposition mapping
 no numeric value
 not mirrored
 no case mapping