ug_ch5c.htm

db.* (pronounced dee-be star) is an advanced, high performance, small footprint embedded database fo

<td width="18%" valign="top">
<p><font size="2"><b>z,z,0,Z</b></font></p>
</td>
<td width="82%" valign="top">
<p><font size="2"><b>bb5</b></font></p>
</td>
</tr>
<tr>
<td width="18%" valign="top">&nbsp;</td>
<td width="82%" valign="top">
<p><font size="2"><b>aB6</b></font></p>
</td>
</tr>
<tr>
<td width="18%" valign="top">&nbsp;</td>
<td width="82%" valign="top">
<p><font size="2"><b>Ab7</b></font></p>
</td>
</tr>
<tr>
<td width="18%" valign="top">&nbsp;</td>
<td width="82%" valign="top">
<p><font size="2"><b>BB8</b></font></p>
</td>
</tr>
</table>
<p><font size="2">The left column below shows how this data would
be sorted. The right column shows the internal representation used
during the sort.</font></p>
<table cellspacing="0" border="0" cellpadding="7" width="450">
<tr>
<td width="19%" valign="top">
<p><font size="2"><b>AA3</b></font></p>
</td>
<td width="81%" valign="top">
<p><font size="2"><b>AA3</b></font></p>
</td>
</tr>
<tr>
<td width="19%" valign="top">
<p><font size="2"><b>aa4</b></font></p>
</td>
<td width="81%" valign="top">
<p><font size="2"><b>AA4</b></font></p>
</td>
</tr>
<tr>
<td width="19%" valign="top">
<p><font size="2"><b>ab1</b></font></p>
</td>
<td width="81%" valign="top">
<p><font size="2"><b>AB1</b></font></p>
</td>
</tr>
<tr>
<td width="19%" valign="top">
<p><font size="2"><b>AB2</b></font></p>
</td>
<td width="81%" valign="top">
<p><font size="2"><b>AB2</b></font></p>
</td>
</tr>
<tr>
<td width="19%" valign="top">
<p><font size="2"><b>aB6</b></font></p>
</td>
<td width="81%" valign="top">
<p><font size="2"><b>AB6</b></font></p>
</td>
</tr>
<tr>
<td width="19%" valign="top">
<p><font size="2"><b>Ab7</b></font></p>
</td>
<td width="81%" valign="top">
<p><font size="2"><b>AB7</b></font></p>
</td>
</tr>
<tr>
<td width="19%" valign="top">
<p><font size="2"><b>bb5</b></font></p>
</td>
<td width="81%" valign="top">
<p><font size="2"><b>BB5</b></font></p>
</td>
</tr>
<tr>
<td width="19%" valign="top">
<p><font size="2"><b>BB8</b></font></p>
</td>
<td width="81%" valign="top">
<p><font size="2"><b>BB8</b></font></p>
</td>
</tr>
</table>
<p><font size="2">Note that case in the original data is intermixed
after the sorting. Because of the zero subsort value, if we used
<b>d_recwrite</b> to change the <b>bb5</b> to <b>BB5</b>,
<b><i>db.*</i></b> would not write the change to disk since,
according to the country table, the data did not change. Note that
this mapping of the lowercase letters to the uppercase letters with
a subsort value of zero is exactly what <b>ignorecase</b>
(explained later in this section) does in the country
table.</font></p>
<p>Suppose we use the same data with the same country table but we
change all the subsort values to one as listed below,</p>
<table cellspacing="0" border="0" cellpadding="7" width="450">
<tr>
<td width="19%" valign="top">
<p><font size="2"><b>a,a,1,A</b></font></p>
</td>
<td width="81%" valign="top">
<p><font size="2"><b>ab1</b></font></p>
</td>
</tr>
<tr>
<td width="19%" valign="top">
<p><font size="2"><b>b,b,1,B</b></font></p>
</td>
<td width="81%" valign="top">
<p><font size="2"><b>AB2</b></font></p>
</td>
</tr>
<tr>
<td width="19%" valign="top">
<p><font size="2"><b>c,c,1,C</b></font></p>
</td>
<td width="81%" valign="top">
<p><font size="2"><b>AA3</b></font></p>
</td>
</tr>
<tr>
<td width="19%" valign="top">
<p><font size="2"><b>...</b></font></p>
</td>
<td width="81%" valign="top">
<p><font size="2"><b>aa4</b></font></p>
</td>
</tr>
<tr>
<td width="19%" valign="top">
<p><font size="2"><b>z,z,1,Z</b></font></p>
</td>
<td width="81%" valign="top">
<p><font size="2"><b>bb5</b></font></p>
</td>
</tr>
<tr>
<td width="19%" valign="top">&nbsp;</td>
<td width="81%" valign="top">
<p><font size="2"><b>aB6</b></font></p>
</td>
</tr>
<tr>
<td width="19%" valign="top">&nbsp;</td>
<td width="81%" valign="top">
<p><font size="2"><b>Ab7</b></font></p>
</td>
</tr>
<tr>
<td width="19%" valign="top">&nbsp;</td>
<td width="81%" valign="top">
<p><font size="2"><b>BB8</b></font></p>
</td>
</tr>
</table>
<p><font size="2">The sorting sequence will be changed from the
normal ASCII ordering below</font></p>
<p><b>A B C ... Z ... a b c ... z</b></p>
<p>to the new ordering of:</p>
<p><b>A a B b C c ... Z z</b></p>
<p>The left column below shows how the above data will be sorted.
The right column shows the internal representation used during the
sort.</p>
<table cellspacing="0" border="0" cellpadding="7" width="450">
<tr>
<td width="19%" valign="top">
<p><font size="2"><b>AA3</b></font></p>
</td>
<td width="81%" valign="top">
<p><font size="2"><b>A A 3</b></font></p>
</td>
</tr>
<tr>
<td width="19%" valign="top">
<p><font size="2"><b>AB2</b></font></p>
</td>
<td width="81%" valign="top">
<p><font size="2"><b>A B 2</b></font></p>
</td>
</tr>
<tr>
<td width="19%" valign="top">
<p><font size="2"><b>Ab7</b></font></p>
</td>
<td width="81%" valign="top">
<p><font size="2"><b>A B'7</b></font></p>
</td>
</tr>
<tr>
<td width="19%" valign="top">
<p><font size="2"><b>aa4</b></font></p>
</td>
<td width="81%" valign="top">
<p><font size="2"><b>A'A'4</b></font></p>
</td>
</tr>
<tr>
<td width="19%" valign="top">
<p><font size="2"><b>aB6</b></font></p>
</td>
<td width="81%" valign="top">
<p><font size="2"><b>A'B 6</b></font></p>
</td>
</tr>
<tr>
<td width="19%" valign="top">
<p><font size="2"><b>ab1</b></font></p>
</td>
<td width="81%" valign="top">
<p><font size="2"><b>A'B'1</b></font></p>
</td>
</tr>
<tr>
<td width="19%" valign="top">
<p><font size="2"><b>BB8</b></font></p>
</td>
<td width="81%" valign="top">
<p><font size="2"><b>B B 8</b></font></p>
</td>
</tr>
<tr>
<td width="19%" valign="top">
<p><font size="2"><b>bb5</b></font></p>
</td>
<td width="81%" valign="top">
<p><font size="2"><b>B'B'5</b></font></p>
</td>
</tr>
</table>
<p><font size="2">Since the subsort value of one means that the
input characters are not identical, <b>bb5</b> could be easily
changed to <b>BB5</b> because <b><i>db.*</i></b> would see the
<b>bb</b> and <b>BB</b> as <i>not</i> exactly the same.</font></p>
<p>One other point to note is that the country table processing is
a one-pass lookup; it will not recursively lookup characters. For
example,</p>
<p><b>d,d,0,a<br>
a,a,0,A</b></p>
<p>maps <b>d</b> to <b>a</b> and also maps <b>a</b> to <b>A</b>.
However, transitive properties do not apply, which means that
<b>d</b> would not be mapped to <b>A</b>. To get <b>a</b> and
<b>d</b> to be sorted as the same character(s), the exact sort-as
string must be used for both as shown below:</p>
<p><b>d,d,X,A<br>
a,a,X,A</b></p>
<p>An additional country table directive may appear as the first
line in <b>db.star.ctb</b>. The first line may say
<b>ignorecase</b>, which will cause all lowercase letters <b>(a</b>
- <b>z)</b> to have their <b>sort-as</b> characters changed to
their uppercase counterparts (<b>A</b> - <b>Z</b>) using a subsort
value of zero. Sorting will ignore the case of the letters, but the
display of the characters will not be changed. If the
<b>ignorecase</b> option is not used, it is necessary to specify
all of the sort-as characters in uppercase to get the same
effect.</p>
<p>A possible German country table is shown below:</p>
<p><b>&Auml;,&Auml;,0,AE<br>
&auml;,&auml;,0,ae<br>
&Uuml;,&Uuml;,0,UE<br>
&uuml;,&uuml;,0,ue<br>
&Ouml;,&Ouml;,0,OE<br>
&ouml;,&ouml;,0,oe<br>
&szlig;,&szlig;,0,ss</b></p>
<p>Case insensitivity for the same data would be indicated as
follows:</p>
<p><b>ignorecase<br>
&Auml;,&Auml;,0,AE<br>
&auml;,&auml;,0,AE<br>
&Uuml;,&Uuml;,0,UE<br>
&uuml;,&uuml;,0,UE<br>
&Ouml;,&Ouml;,0,OE<br>
&ouml;,&ouml;,0,OE<br>
&szlig;,&szlig;,0,SS</b></p>
<p>A an example, given the case-sensitive, German table above, the
string "&Auml;lan" would be sorted as if it was the string
"AElan".</p>
<p>Note: The country table file is a binary file that just happens
to contain only text data. Usually the country table file will be
created though the use of a text editor. However, some text editors
put end-of-file (EOF) markers (ASCII 26) at the end of files they
create. It is important to ensure your editor does not do this as
it will cause problems during the interpretation of the file; the
EOF marker will be treated as part of the string being read from
the file.</p>
<p>The functionality of the country table can be created
programmatically using the <b>d_mapchar</b> and <b>d_on_opt</b>
functions (see the function descriptions in the <b><i>db.*</i>
Reference Manual</b>). The following calls can be made before
opening the database to create the case-sensitive German character
set mapping (note the change in the parameter ordering):</p>
<pre>
<font color=
"#0000FF">d_mapchar( '&Auml;', '&Auml;', "AE", 0, task );
d_mapchar( '&auml;', '&auml;', "ae", 0, task );
d_mapchar( '&Uuml;', '&Uuml;', "UE", 0, task );
d_mapchar( '&uuml;', '&uuml;', "ue", 0, task );
d_mapchar( '&Ouml;', '&Ouml;', "OE", 0, task );
d_mapchar( '&ouml;', '&ouml;', "oe", 0, task );
d_mapchar( '&szlig;', '&szlig;', "ss", 0, task );
</font>
</pre>
<p><font size="2">This is the case insensitive option:</font></p>
<pre>
<font color="#0000FF">d_on_opt( IGNORECASE );
d_mapchar( '&Auml;', '&Auml;', "AE", 0, task );
d_mapchar( '&auml;', '&auml;', "AE", 0, task );
d_mapchar( '&Uuml;', '&Uuml;', "UE", 0, task );
d_mapchar( '&uuml;', '&uuml;', "UE", 0, task );
d_mapchar( '&Ouml;', '&Ouml;', "OE", 0, task );
d_mapchar( '&ouml;', '&ouml;', "OE", 0, task );
d_mapchar( '&szlig;', '&szlig;', "SS", 0, task );
</font>
</pre>
<p><font size="2">The use of the functions eliminates the need for
the country table file, but there are big disadvantages to using
the functions instead of the country table file. The country table
file is used by all <b><i>db.*</i></b> utilities and applications
that call <b>d_open</b>. Hence if a database is built by an
application using the above function calls, and a utility such as
<b>ida</b> is used on the database, it may find the keys in an
order other than expected. Worse yet, if it adds keys to the
database, it will do so with a different collating sequence, which
will cause the key files to become corrupted.</font></p>
<p><font size="2">The safest way to use international characters is
to define them in a country table that will always be used when the
database is used. If the function calls are used in application
code (to eliminate the extra file), it will still be necessary to
use a country table file when the utilities are used on the same
database. Alternatively, the <b>ignorecase</b> and CTBPATH
information can be put into the <b>db.star.ini</b> file.</font></p>
<p><a href="UG_Ch6.htm">Next Page</a></p>
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