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<HTML>
<HEAD>
<TITLE>BoPoMoFo system and encoding in libtabe</TITLE>
</HEAD>
<BODY>
<H2>Table Of Content</H2>
<OL>
<LI><A HREF="#intro">Introduction</A>
<LI><A HREF="#encoding">Encoding System</A>
<LI><A HREF="#credits">Credits</A>
</OL>
<HR>
<H2><A NAME="intro">Introduction</A></H2>
<P>
<I>BoPoMoFo</I>, similar to PinYin or other Romanization system used
elsewhere, is the most common method for learning Mandarin/Chinese
pronunciation in Taiwan area. The system consists of 37 phonetic
plus 5 tone symbols. Each basic pronunciation of Chinese is made up
of at most 3 phonetic symbols and exactly one tone symbol. Each of
the 37 phonetic symbol can appear once in a pronunciation, and not all
the combinations of phonetic symbols are meaningful. The 37 phonetic
symbols are exclusively divided into 3 groups, only one symbols out
of a group can be used to make up pronunciation. The 3 phonetic
symbols used to make up a pronunciation come out of the 3 groups, one
for each group.
</P>
<H2><A NAME="encoding">Encoding System</A></H2>
<P>
Each of the 37 phonetic symbols are assigned number for 1 to 37. The 5
tone symbols are assigned number from 38 to 42. `0' is used to
designate there's no symbol in the position. The word `electricity''s
pronunciation code thus is (5, 22, 33, 41).
</P>
<P>
To help processing of the code, we designed an encoding system that
uses 15bit, i.e., less than 2 bytes to represent it. The reason is
try to maintain all the combinations while be space-efficient. The
first group have phonetic symbols has 21 symbols, the second group has
3, the third group has 13, as shown in Table 1. So we use 6 bits for
the first group, 2 bits for the second group and 4 bits for the third
group, plus 3 bits for the tone symbols.
</P>
<TABLE BORDER="2" CELLPADDING="5" ALIGN="CENTER">
<TH></TH>
<TH>1st Group</TH>
<TH>2nd Group</TH>
<TH>3rd Group</TH>
<TH>Tone Symbols</TH>
<TR>
<TH># of Symbols</TH>
<TD>21</TD>
<TD>3</TD>
<TD>13</TD>
<TD>5</TD>
<TR>
<TH># of Bits</TH>
<TD>6</TD>
<TD>2</TD>
<TD>4</TD>
<TD>3</TD>
<TR>
</TABLE>
<BR>
<CENTER>Table 1. Numbers and Bits of Each BoPoMoFo Group</CENTER>
<P>
The symbol value stored is the offset in it's group plus 1. (0 is
reserved) So the encoding for the example code in the previous
paragraph is
<BLOCKQUOTE>
"0 000101<TT>(5)</TT> 01<TT>(22-21=1)</TT>
1001<TT>(33-24=9)</TT> 100<TT>(41-37=4)</TT>"
</BLOCKQUOTE>
It's 2764 in decimal. All the pronunciation related functions used the
encoding as internal pronunciation representations and storage format.
</P>
<H2><A NAME="credits">Credits</A></H2>
<P>
The encoding system was inspired by the ETen Chinese System's hashing
function, and brought to attention by Yung-Ching Hsiao.
</P>
<HR>
<CENTER>
<TINY>
$Id: BoPoMoFo.shtml,v 1.2 2001/08/20 03:53:02 thhsieh Exp $<BR>
Copyright 2000, libtabe Project. All rights reserved.
</TINY>
</CENTER>
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