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Initial revision X-SVN-Rev: 2
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<title>International Classes for Unicode - Collation</title>
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Initial revision X-SVN-Rev: 2
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</head>
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<body bgcolor=white lang=EN-US link=blue vlink=blue style='tab-interval:.5in'>
Initial revision X-SVN-Rev: 2
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<div class=Section1>
ICU-227 backslashes X-SVN-Rev: 805
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<h1>International Components for Unicode</h1>
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<h2>Collation Framework</h2>
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<div class=MsoNormal align=center style='text-align:center'>
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</div>
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<h3><u>Contents</u></h3>
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<ul type=disc>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l4 level1 lfo1;tab-stops:list .5in'>What is collation?</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l4 level1 lfo1;tab-stops:list .5in'>The rule symbols and their
usage</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l4 level1 lfo1;tab-stops:list .5in'>Interesting Examples</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l4 level1 lfo1;tab-stops:list .5in'>Implementation Details</li>
<ul type=circle>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:
auto;mso-list:l4 level2 lfo1;tab-stops:list 1.0in'>Building the Collation
Table</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:
auto;mso-list:l4 level2 lfo1;tab-stops:list 1.0in'>Incremental Comparison
Diagram</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:
auto;mso-list:l4 level2 lfo1;tab-stops:list 1.0in'>Generating a Collation
Table</li>
</ul>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l4 level1 lfo1;tab-stops:list .5in'>Q and A</li>
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</ul>
<h3><u>What is collation?</u></h3>
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<p>Collation framework performs locale-sensitive string comparison. The user of
this class can use this class to build searching and sorting routines for
natural language text, build table of contents for large documentation or
create efficient index look up for database entries.<br>
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<br>
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The ICU Collator classes provides services to allow: </p>
<ul type=disc>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l10 level1 lfo2;tab-stops:list .5in'>Simple, data-driven, table
based collation.</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l10 level1 lfo2;tab-stops:list .5in'>Easily customizble for your
needs.</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l10 level1 lfo2;tab-stops:list .5in'>Merging different resources
made possible.</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l10 level1 lfo2;tab-stops:list .5in'>Behind the scene
transforming the ASCII data file into a binary file for efficiency.</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l10 level1 lfo2;tab-stops:list .5in'>Offering both incremental
comparison for simple comparison and collation keys for batch processes.</li>
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</ul>
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<p>There are 4 comparison levels in the Collator classes to allow different
levels of difference to be considered significant: </p>
<ul type=disc>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l6 level1 lfo3;tab-stops:list .5in'>Primary: a letter difference.
For example, 'a' and 'b'.</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l6 level1 lfo3;tab-stops:list .5in'>Secondary: an accent
difference. For example, '<27>' and '<27>'.</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l6 level1 lfo3;tab-stops:list .5in'>Tertiary: a case difference.
For example, 'a' and 'A'.</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l6 level1 lfo3;tab-stops:list .5in'>Identical: no difference. For
example, 'a' and 'a'.</li>
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</ul>
<h3><u>The rule symbols and their usage</u></h3>
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<p>A string is decomposed to be one or more collation elements when using with
the collation classes. The collation rules specify the order of these collation
elements. The collation table is composed of a list of collation rules, where
each rule is of three forms: </p>
<ol start=1 type=1>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l3 level1 lfo4;tab-stops:list .5in'>&lt;modifier&gt;</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l3 level1 lfo4;tab-stops:list .5in'>&lt;relation&gt;
&lt;text-argument&gt;</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l3 level1 lfo4;tab-stops:list .5in'>&lt;reset&gt;
&lt;text-argument1&gt; &lt;relation&gt; &lt;text-argument2&gt;</li>
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</ol>
<h4>&lt;modifier&gt;</h4>
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<ul type=disc>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l7 level1 lfo5;tab-stops:list .5in'>'@': French secondary, accent
weights sorted backwards.</li>
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</ul>
<h4>&lt;text-argument&gt;</h4>
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<p>A text-argument is any sequence of characters, excluding special characters
(that is, common whitespace characters [0009-000D, 0020] and rule syntax
characters [0021-002F, 003A-0040, 005B-0060, 007B-007E]). If those characters
are desired, you can put them in single quotes (e.g. ampersand =&gt; '&amp;').
Note that unquoted white space characters are ignored; e.g. &quot;b c&quot; is
treated as &quot;bc&quot;.</p>
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<h4>&lt;relation&gt;</h4>
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<ul type=disc>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l9 level1 lfo6;tab-stops:list .5in'>'&lt;' : Greater, as a letter
difference (primary)</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l9 level1 lfo6;tab-stops:list .5in'>';' : Greater, as an accent
difference (secondary)</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l9 level1 lfo6;tab-stops:list .5in'>',' : Greater, as a case
difference (tertiary)</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l9 level1 lfo6;tab-stops:list .5in'>'=' : Equal</li>
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</ul>
<h4>&lt;reset&gt;</h4>
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<ul type=disc>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l0 level1 lfo7;tab-stops:list .5in'>'&amp;': Indicates that
text-argument2 follows the position to where the reset text-argument1
would be sorted.</li>
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</ul>
<h3><u>Interesting Examples</u></h3>
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<p>The following is a list of interesting examples of the rules and some string
comparison results using those rules. The comparison relation will be denoted
as &quot;&lt;&quot; of primary difference of less than, &quot;&lt;&lt;&quot; of
secondary difference of less than, &quot;&lt;&lt;&lt;&quot; of teriatry
difference of less than and &quot;==&quot; of equal to relationships: </p>
<ul type=disc>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l1 level1 lfo8;tab-stops:list .5in'>Rule &quot; a, A &lt; b, B
&lt; c, C &lt; ch, cH, Ch, CH &lt; d, D &lt; e, E&quot;: this rule simply
says, sorts letters 'a', 'b', 'c', 'd' and 'e' in that order with primary
weights. 'ch' is sorted as a significant letter between 'c' and 'd' with
primary weights and upper cased letters sorts after lower cased letters
with tertiary weights. For example, &quot;abc&quot; &lt;&lt;&lt;
&quot;ABC&quot; and &quot;achb&quot; &lt; &quot;adb&quot;.</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l1 level1 lfo8;tab-stops:list .5in'>Rule &quot; a, A &lt; b, B
&lt; c, C &lt; d, D &lt; e, E &amp; AE; <20> &quot;: this will sort letters
'a', 'b', 'c', 'd' and 'e' in that order with primary weights. '<27>' will
sort as with a secondary less than to the sequence of 'A' following 'E'.
For example, &quot;aeb&quot; &lt;&lt; &quot;<EFBFBD>b&quot; and &quot;acb&quot;
&lt; &quot;<EFBFBD>b&quot;.</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l1 level1 lfo8;tab-stops:list .5in'>Rule &quot;.... q, Q &amp;
Question'-'mark = '?' ....&quot;: the rule shows how to sort symbols to be
equivalent to the corrsponding text. In this example, &quot;?&quot; ==
&quot;Question-mark&quot;. Note that the special symbols need to be quoted
in the rule.</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l1 level1 lfo8;tab-stops:list .5in'>Rule &quot;.... &amp; aa ; a-
&amp; ee ; e- &amp; ii ; i- &amp; oo ; o- &amp; uu ; u- ....&quot;: this
rule demonstrates how to specify prolonged vowels in Japanese. In this
case, &quot;aa&quot; is sorted as with a secondary less than to
&quot;a-&quot;. For example, &quot;baab&quot; &lt;&lt; &quot;ba-b&quot;.</li>
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</ul>
<h3><u>Implementation Details</u></h3>
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<p>Three parts of the code will be carefully examined here: </p>
<ul type=disc>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l5 level1 lfo9;tab-stops:list .5in'>Building the collation rule
table. (see mergecol.cpp, ptnentry.cpp and tblcoll.cpp)</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l5 level1 lfo9;tab-stops:list .5in'>Incremental comparison
algorithm for simple string comparison. (RuleBasedCollator.compare() in
tblcoll.cpp)</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l5 level1 lfo9;tab-stops:list .5in'>Collation key generation and
its format. (RuleBasedCollator.getCollationKey() in tblcoll.cpp)</li>
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</ul>
<h3><u>Building the Collation Table</u></h3>
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<p>The process of building a collation table is as following: </p>
<ul type=disc>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l8 level1 lfo10;tab-stops:list .5in'>Parse the rule text into a
list of pattern entries. Each pattern has the content of current core
characters, extension character and the strength relation. (In
ptnentry.cpp)</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l8 level1 lfo10;tab-stops:list .5in'>Inserts each entry at the
correct position based on the &lt;reset&gt; arguements. (In mergecol.cpp)</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l8 level1 lfo10;tab-stops:list .5in'>Build the compacted, highly
efficient look-up table based on the list of pattern entries. (In
tblcoll.cpp)</li>
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</ul>
<p>&nbsp;</p>
<h3><u>Incremental Comparison Diagram</u></h3>
<p>&nbsp;</p>
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<p><img width=468 height=800 id="_x0000_i1026" src=collflow.gif></p>
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<h3><u>Generating a Collation Key</u></h3>
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<p>The control flow of generating a collation key is as the following: </p>
<ol start=1 type=1>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l2 level1 lfo11;tab-stops:list .5in'>Retrieve the next collation
element of the source string. Go to step 5 when reaches the end of string.</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l2 level1 lfo11;tab-stops:list .5in'>Append the primary weight of
element to the primary weight buffer.</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l2 level1 lfo11;tab-stops:list .5in'>Checks if it's necessary to
process secondary weights. If so, append the secondary weights to the
secondary weight buffer. If the collator is marked to process French
secondary, reverse the order of all the secondary weights before encounters
the next primary weight.</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l2 level1 lfo11;tab-stops:list .5in'>Checks if it's necessary to
process tertiary weights. If so, append the tertiary weights to the
tertiary weight buffer. </li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l2 level1 lfo11;tab-stops:list .5in'>Concatenate the primary
weight buffer, secondary weight buffer and tertiary weight buffer and add
a null delimiter among the weights. Return the concatenated buffer as the
collation key.</li>
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</ol>
<h3><u>Q &amp; A</u></h3>
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<ol start=1 type=1>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l11 level1 lfo12;tab-stops:list .5in'>How do I customize the
collation sequence?<br>
A: Using the RuleBasedCollator constructor, the user of the collation
framework can then create his/her own Collator with a customized rule.</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l11 level1 lfo12;tab-stops:list .5in'>Will the collation framwork
support the surrogate and private use characters?<br>
A: It's part of our future work items.&nbsp; However, no firm schedule has
been set for this yet.</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l11 level1 lfo12;tab-stops:list .5in'>How does the French
secondary turn-on affect the generation of collation key?<br>
A: In French, the secondary differences are sorted backwards so this will
invoke the collation key to reverse the secondary weights in the keys.</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l11 level1 lfo12;tab-stops:list .5in'>Is there any support for
composing characters? If so, how does it work?<br>
A: Yes, it is based on the Normalizer interface.&nbsp; When a expanding
character is detected, the rule builder will construct collation entries
for the precomposed version internally to handle the composed characters
correctly.</li>
<li class=MsoNormal style='mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;
mso-list:l11 level1 lfo12;tab-stops:list .5in'>Is there any plan for
performance improvement, for instance, contracting/expanding character
lookup?<br>
A: Yes, the performance enhancement is an ongoing work item.</li>
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</ol>
<p>&nbsp;</p>
ICU-227 backslashes X-SVN-Rev: 805
2000-02-21 21:38:59 +00:00
<p><a href="../readme.html">ReadMe for </a><a href="../readme.html#API">International
Components for Unicode</a></p>
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<div class=MsoNormal align=center style='text-align:center'>
<hr size=2 width="100%" align=center>
</div>
</div>
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</body>
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Initial revision X-SVN-Rev: 2
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</html>
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