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<h1>The Gedcom parser library</h1>
<div align="left">The intention of this page is to provide some explanation
of the gedcom parser, to aid development on and with it. First,
some practical issues of testing with the parser will be explained.<br>
- <br>
+<br>
+<h2>Index</h2>
+<ul>
+ <li><a href="#Testing">Testing</a></li>
+ <ul>
+ <li><a href="#Basic_testing">Basic testing</a></li>
+ <li><a href="#Preparing_for_further_testing">Preparing for further testing</a></li>
+ <li><a href="#Testing_the_parser_with_debugging">Testing the parser with debugging</a></li>
+ <li><a href="#Testing_the_lexers_separately">Testing the lexers separately</a><br>
+ </li>
+ </ul>
+ <li><a href="#Structure_of_the_parser">Structure of the parser</a></li>
+ <ul>
+ <li><a href="#Character_encoding">Character encoding</a><br>
+ </li>
+ </ul>
+</ul>
+<br>
+<hr width="100%" size="2">
+<h2><a name="Testing"></a>Testing<br>
+</h2>
+
-<h2>Basic testing<br>
- </h2>
+<h3><a name="Basic_testing"></a>Basic testing<br>
+
+ </h3>
+
You should be able to perform a basic test using the commands:<br>
<blockquote><code>./configure<br>
make check</code><br>
</blockquote>
If everything goes OK, you'll see that some gedcom files are parsed,
- and that each parse is successful. Note that the used gedcom files
+ and that each parse is successful. Note that some of the used gedcom files
are made by <a href="http://heiner-eichmann.de/gedcom/gedcom.htm">Heiner
Eichmann</a> and are an excellent way to test gedcom parsers thoroughly.<br>
<br>
- <h2>Preparing for further testing</h2>
- The basic testing described above doesn't show anything else than
-"Parse succeeded", which is nice, but not very interesting. Some
+
+ <h3><a name="Preparing_for_further_testing"></a>Preparing for further testing</h3>
+Some
more detailed tests are possible, via the <code>testgedcom</code> program
-that is generated by <code>make test</code>. <br>
+that is generated by <code>make</code>. <br>
<br>
However, since the output that <code>testgedcom</code> generates
is in UTF-8 format (more on this later), some preparation is necessary
and see the result.<br>
<br>
- <h2>Testing the parser with debugging</h2>
+
+ <h3><a name="Testing_the_parser_with_debugging"></a>Testing the parser with debugging</h3>
+
Given the UTF-8 capable terminal, you can now let the <code>testgedcom</code>
program print the values that it parses. An example of a command
line is (in the <code>gedcom</code> directory):<br>
show a lot of special characters.<br>
<br>
- <h2>Testing the lexers separately</h2>
+
+ <h3><a name="Testing_the_lexers_separately"></a>Testing the lexers separately</h3>
+
The lexers themselves can be tested separately. For the 1-byte
lexer (i.e. supporting the encodings with 1 byte per characters, such as
- ASCII, ANSI and ANSEL), the sequence of commands would be:<br>
+ ASCII, ANSI and ANSEL), the command would be (in the <code>gedcom</code> subdirectory):<br>
- <blockquote><code>make clean<br>
- make test_1byte<br>
+ <blockquote><code>make lexer_1byte<br>
</code></blockquote>
- This will show all tokens in the <code>t/allged.ged</code> test file.
- Similar tests can be done using <code>make test_hilo</code> and <code>
-make test_lohi</code> (for the unicode lexers).<br>
+ This will generate a lexer program that can process e.g. the <code>t/allged.ged</code>
+ test file. Simply cat the file through the lexer on standard input
+and you should get all the tokens in the file. Similar tests can be
+done using <code>make lexer_hilo</code> and <code>
+make lexer_lohi</code> (for the unicode lexers). In each of the cases you need to know yourself which of the test files are appropriate to pass through the lexer.<br>
<br>
This concludes the testing setup. Now for some explanations...<br>
- <br>
+ <hr width="100%" size="2"><br>
- <h2>Structure of the parser</h2>
+ <h2><a name="Structure_of_the_parser"></a>Structure of the parser</h2>
I see the structure of a program using the gedcom parser as follows:<br>
<br>
<img src="images/schema.png" alt="Gedcom parsing scheme">
<br>
<br>
<br>
- TO BE COMPLETED...<br>
+ The parser is based on <code>lex/yacc</code>, which means that a module generated by <code>lex</code>
+ takes the inputfile and determines the tokens in that file (i.e. the smallest
+units, such as numbers, line terminators, GEDCOM tags, characters in GEDCOM
+values...). These tokens are passed to the parser module, which is
+generated by yacc, to parse the syntax of the file, i.e. whether the tokens
+appear in a sequence that is valid. <br>
+ <br>
+For each recognized statement in the GEDCOM file, the parser calls some callbacks,
+which can be registered by the application to get the information out of
+the file.<br>
+ <br>
+This basic description ignores the problem of character encoding. The next section describes what this problem exactly is.<br>
+ <br>
+ <h3><a name="Character_encoding"></a>Character encoding</h3>
+ <h4><i>The character encoding problem</i><br>
+ </h4>
+Developers are usually familiar with the ASCII character set. This
+is a character set that assigns a unique number to some characters, e.g.
+an "A" has ASCII code 65 (or 0x41 in hex), and an "a" has ASCII code 97 (or
+0x61 in hex). Some people may also have used ASCII codes for several
+drawing characters (such as a horizontal bar, a vertical bar, or a top-right
+corner) in the old DOS days, to be able to draw nice windows in text mode.<br>
+ <br>
+However, these last characters are strictly spoken not part of the ASCII
+set. The standard ASCII set contains only the character positions from
+0 to 127 (i.e. anything that fits into an integer that is 7 bits wide). An
+example of this table can be found <a href="http://web.cs.mun.ca/%7Emichael/ascii-table.html">here</a>. Anything that has an ASCII code between 128 and 255 is in principle undefined.<br>
+ <br>
+Now, several systems (including the old DOS) have defined those character
+positions anyway, but usually in totally different ways. Some well
+known extensions are:<br>
+ <ul>
+ <li>the <a href="http://czyborra.com/charsets/cp437.gif">DOS</a>
+ character set, nowadays usually known as Code Page 437, but sometimes also
+named LatinUS, ECS (Extended Character Set) or PC-8; note that the table
+displayed in the link also contains the standard ASCII part</li>
+ <li>the <a href="http://czyborra.com/charsets/cp1252.gif">ANSI</a> character set, also known as Code Page 1252, and usually the default on Windows</li>
+ <li>the <a href="http://czyborra.com/charsets/iso8859-1.gif">ISO-8859-1</a> character set (also called Latin-1), which is an ISO standard for Western European languages, mostly used on various Unices</li>
+ <li>the <a href="http://czyborra.com/charsets/adobe-stdenc.gif">Adobe Standard Encoding</a>, which is by default used in Postscript, unless overridden</li>
+ </ul>
+And these are only examples of character sets used in West-European languages.
+ For Japanese, Chinese, Korean, Vietnamese, ... there are separate character
+sets in which one byte's meaning can even be influenced by what the previous
+byte was, i.e. these are multi-byte character sets. This is because
+even 256 characters is totally inadequate to represent all characters in
+such languages.<br>
+ <br>
+So, summarizing, if a text file contains a byte that has a value 65, it is
+pretty safe to assume that this byte represents an "A", if we ignore the
+multi-byte character sets spoken of before. However, a value 233 cannot
+be interpreted without knowing in which character set the text file is written.
+ In Latin-1, it happens to be the character "é", but in another
+character set it can be something totally different (e.g. in the DOS character
+set it is the Greek letter theta).<br>
+ <br>
+Vice versa, if you need to write a character "é" to a file, it depends
+on the character set you will use what the numerical value will be in the
+file: in Latin-1 it will be 233, but if you use the DOS character set it
+will be 130.<br>
+ <br>
+ <h4><i>Unicode</i></h4>
+Enter the Unicode standard...<br>
+ <br>
+TO BE COMPLETED<br>
+
<hr width="100%" size="2">
- <pre>$Id$<br>$Name$<br></pre>
+ <pre><font size="-1">$Id$<br>$Name$</font><br></pre>
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