Technical documentation of the corpus conversion process

Conversion process

This text in Spanish ~ Este texto en español (translation: Maria Ramos)

This document describes the more technical side of the corpus infrastructure. The document corpus_conversion.html contains the user documentation as well as the description of the basic infrastructure. The usage of the script convert2xml.pl is documented there, this document describes the contents of the script.

All the binaries and scripts used in the corpus conversion process are stored under $GTHOME/gt/script/corpus, except the tools that are already installed to some common bin. The xsl-files which transfer the structural information of different source files (docbook2xml.xsl and xhtml2xml.xsl) and the template for file specific xsl-files (XSL-template.xsl) are also stored there. The directory $GTFREE|$GTBOUND/tmp/ is reserved for temporary files and log files that are created during the conversion. The log files contain the system commands executed during the conversion as well as the warnings and error messages. The log file is named after the file that is converted.

The next sections describe the conversion processes for each document type and the tools used. The conversion includes hyphen-detection and language recognition as well as decoding the wrongly utf-8 -encoded characters.

Word documents

Microsoft Word documents are converted with the program antiword to produce a docbook xml, and piped to the xslt program xsltproc, that converts to our XML-format. We have an xsl-document docbook2corpus.xsl, that is used in converting the document.

RTF documents

RTF documents are converted to html using unrtf, then to our xml format using xhtml2xml.xsl.

Ávvir xml documents

These documents are converted to our xml format using avvir2corpus.xsl

SVG documents

These documents are converted to our xml format using svg2corpus.xsl

Plain text document

Plain text documents that are stored to the database should have the extension .txt. The encoding of a text document is solved using the iconv -tool. If there are special markings for headings and paragraphs, like in some newspaper texts, they are used in creating the document structure. Otherwise, the empty lines mark paragraph breaks and short lines beginning with numbers are treated as titles.

Adobe document

Pdf documents are converted to plain text using pdftotext, and then converted to our xml format using langTools::Corpus::txt_clean

Web-document

Web documents are first cleaned using the program HTML Tidy , using several command line options.. The output is converted to xml using the xsl-file xhtml2xml.xsl.

Paratext document

Paratext is a file format for publishing and interchanging basic Scripture texts in multiple languages. It is intended to be used for all aspects for Bible layout and publishing. The paratext format is based on backslash codes, format called USFM, see e.g http://confluence.ubs-icap.org/display/USFM/Home The paratext files are converted using a Perl script paratext2xml.pl which forms basic xml-structure which roughly corresponds our corpus.dtd. The files that are added to the corpus repository should have the suffix .ptx.

Hyphenation: add-hyph-tags.pl

    Usage: add-hyph-tags.pl [OPTIONS] FILES
    Tag the hyphenation marks.
    Options
    --all            search the whole text for hyphenation points.
                 The default is to search only the end of the lines.
    --infile=<file>  the input file.
    --outfile=<file> output file.
    --help           prints the help text and exit.

The script replaces hyphens in the text with tag <hyph/>. The hyphens are searched by default at the end of the line. The option --all can be used for replacing the hyphens all over the text. The aim of the script is to replace only "real" hyphens, i.e. the ones that mark real hyphenation points. The hyphens in e.g. numeric expressions are not replaced. The words which precede a hyphen but are not hyphenation points such as "ja" in expression "davvi-, julev- ja oarjelsámegillii" are taken into account.

The reason why the hyphens are tagged by default only at the line ends is the existence of e.g. the following correct hyphenation marks which do not mark a hyphenation point. Some of these occur at the line ends and cause errors.

teknihkalaš-luonddudieđalaš
Norplus-prográmma
norgga-ruoŧa
dánska-norgalaš

The script takes into account the xml-notation of the file. If the last word of a paragraph marked with </p> ends with a hyphen, the next paragraph beginning with <p> is searched for the rest of the word. Some text extraction tools such as antiword may create this kind of structures. The script also reformats the text by removing white space, moving <p>-tags and changing the place of the line break.

Language recognition

The newly created xml-document is parsed and the language of each paragraph is recognized using the tool langrec. The tool is described in the document langrec.html. The langrec tool is not perfect in recognizing different Saami languages using short pieces of text and if the text is very short, it confuses to other languages as well. The tool is improved with word models, which are contain lists of most common words in each language. These wordlists are used in addition to the original language models that generated from text corpus using text_cat. The wordlists are used only if the anguage models failed to produce a unique result. The word models enhance the recognizion of short paragraphs, especially when e.g. Bokmål should be selected instead of some Saami language, since the short uninflected words occur so often also in short pieces of text.

The document always has a main language, and only the differing languages are marked in the xml-structure. By default, all the languages: sme, smj, sma, fin, swe, nob, nno, swe, isl, ger, dan, eng can occur in the document and they are taken into account in the categorization process. However, since the e.g. the different Sámi language easily confuse with each other and Finnish, the language recognizion can be restricted to some subset of these languages. The document can be explicitely marked as monolingual, or multilingual containg text fractions of some of the abovementioned languages. The variables are available in the file-specific xsl-file.

XSLT-scripts

The structural information, such as titles and paragraphs, that is contained in MS Word of pdf document is preserved in the xml-document. The antiword program that is used in converting the Word documents produces xml docbook format. That format is further transformed to our xml-format, using xsl-script docbook2xml.xsl. The similar script xhtml2xml.xsl is used in transforming the structural information in html document to our xml-format. Pdf-files are first converted to html and the same xsl-script is used.

Word documents may contain metainformation, such as the name of the owner of the file, which is preserved as well. The other metainformation is added to the xml-file through the file-specific xsl-script. The process is explained in the usage documentation. The file specific xml-file is copied from the file XSL-template.xsl, located in corp/bin -directory. It contains variables for adding the metainformation. These variables always overrides the metainformation coming from the original document. The metainformation recieved from the web upload script is stored straight to the file-specific xsl-file, so the information can be altered manually.

The script common.xsl contains instructions for building the final xml-structure of the corpus file. The structure is validated against the document type definition, http://giellatekno.uit.no/dtd/corpus.dtd common.xsl is included in every file-specific xsl-script.

There is a special script empty.xsl to be used instead of common.xsl when the document cannot be converted to xml-structure. This can happen for several reasons, but the most common reason is that the character encoding in the original document is somehow broken; the Saami characters may be missing or there are several character encodings used, when the result of the conversion is not satisfactory. The document could be removed from the database as well, but e.g. some newspaper documents are considered to be part of the distribution.

Useful scripts for corpus maintainer

There are several small scripts for corpus database maintenance and cleaning. They reside in gt/script -catalog. The most important ones are listed here:

corpus_summarize.sh
The script is used for generating summarizing information of the corpus files and storing them to cvs, under the catalog gt/doc/lang/corp. The script calls the Perl-script corpus_summary.pl, which generates the summaries. The file corpus-content.xml contains a list of all the files in the corpus database and some relevant information like the license and size. The files corpus-susummary.xml and corpus-summary-YYYY-MM-DD.xml contain the total count of the documents as well as the number of the documents in different subdirectories. The xml-files are further transformed to forrest documentation.
corpus_zip.sh
The script copies the free-catalog from the corpus database and creates zipped tar-archives of it. An archive is created of both the xml files and the files that contain only the extracted text in the selected language. The archives are copied to the download area.
corpus_chmod.sh
The script is used for correcting the group ids and permissions of the corpus files in different catalogs. Running the script requires sudo rights.
change_xsl_generic.py
for i in `find . -name \*.xsl`
do
change_xsl_generic.py translator_fn Pirjo translator_ln Paavaniemi
translator_gender fem translator_nat FI $i
done
gt2ga.sh
Copies the selected files to G5 for analysis, compiles the latest versions of the tools and runs the analysis for the whole corpus. The analyzed files are stored under ga/lang/genre, the whole genre in one file. The script is currently used only in G5.
corpus_fix_meta.sh
Some of the corpus directories contain several files with similar metainformation, e.g. all the newspaper texts may have the same collection information, the name of the newspaper. This script is planned for updating several file-specific xsl-files at the same time. The directory where the files are searched is given in variable inside the script. The script uses xsl-script change_xsl.xsl for the transformation. The xsl-script should be modified for the different uses and the variable containing the path to the script changed. The version control of the xsl-files is handled automatically, although sometimes stealing a lock is necessary and requires some typing.
corpus_rename.sh
The names of the corpus files have to face some basic requirements: They should be in utf-8 encoding, in NFC, not contain any special characters that would harm the shell ("´? etc.), have spaces replaced by underscores or removed and have the correct extensions (.txt, .html, .doc, .pdf or .ptx). This script searches whole directories for filenames and changed them to confront these requirements. If the file already has some extension, it is not changed.
corpus_bad_encoding.sh
Some of the character set conversions do not succeed well enough for the purposes of linguistic analysis. The files may contain different encodings in different parts of the file, single unrecognized characters or the character set is not recognized at all. Those files can be located using this script.
Makefile
There is a Makefile in /usr/local/share/corp for converting files that are not up-to-date concerning the original or file-specific xsl-file. Usage: make LANGUAGE=sme GENRE=facta or make path/to/file.xml.

corpus.dtd

corpus.dtd contains the document type definition for the xml-structure. It is stored in http://giellatekno.uit.no/dtd/corpus.dtdThe fields are briefly described in the following:

document (header,body)

header

The document is divided into to elements: header that contains the metainformation and body for the document content. The header contains the following fields:

title
The title of the document
genre
The document genre can be one of the following: admin, bible, facta, ficti or news.
author+
The author of the document is either person or "unknown".
person
Person consist of following attributes: firstname, lastname, born, sex and nationality.
translator*
If the document is translated, the translator is either "unknown" or person.
translated from*
year?
Publishing year, or if the document is unpublished, the year the document was written.
place?
Publishing place, or if the document is unpublished, the country or place where the document was written.
publChannel
Either publication or unpublished
publication
Consists of elements publisher, ISBN and ISSN.
collection
The name of the journal, book or article collection.
wordcount
availability
Either free or license
license
License type is "standard" or "other". The type "standard" indicates a license agreed with the basic contract
submitter?
The person or instance who stored the document to the database. Contains elements for name and email address.
multilingual?
If the document is multilingual, this element describes the languages that occur in the document.
language+
Language is given as an xml:lang attribute.
origFileName?
The original name of the file. The filename may change during the conversion to xml.
metada
Either "complete" or "uncomplete".
version
Contains version information of different conversion tools.

body

The document body contains sections and text-entities (%text.ent):

%text.ent
Basic text-entites are list, table, p and pre.
section
Contains sections and text-entities.
list
Consists of paragraphs p with type "listitem".
table
Consist of rows:
row
Contains paragraphs p with type "tablecell".
p
The paragraph type is given as an attribute: title, listitem, text or tablecell. Paragraph contains text and elements em, hyph and error:
em
Emphasis type: bold, italic, underline or delimited.
hyph
Empty hyphenation tag
error
Error marking in the text, has the correct replacement as an attribute.
pre
Programlisting or other unformatted text.

Character decoding: samiChar::Decode.pm

Some of the sámi characters are wrongly utf-8-encoded by the conversion tools, like pdftotext. There is a Perl module samiChar::Decode.pm for decoding the sámi characters.

SYNOPSIS

           use samiChar::Decode;

           my $file = "file.txt";
           my $outfile = "file.txt";
           my $encoding;
           my $lang = "sme";

           $encoding = &guess_encoding($file, $lang);
           &decode_file($file, $encoding, $outfile);

           $encoding = &guess_text_encoding($file, $outfile, $lang);
           &decode_text_file($file, $encoding, $outfile);

DESCRIPTION

samiChar::Decode.pm decodes characters to utf-8 byte-wise, using code tables. It is planned for decoding the Saami characters in a situation, where the document is converted to utf-8 without knowing the original encoding. The decoding is implemented by using code table files, so the module can be used for other conversions as well. The output is however always utf-8.

The function guess_encoding is used for guessing the original encoding. It takes into account only the most common Sámi characters and their frequency in the text. The file is further decoded using the function decode_file.The functions guess_text_encoding and decode_text_file can be used for guessing the encoding and decoding a file which is not utf-8 encoded but in it's original encoding. This is the case with many text files that are not converted by any tool. Thes functions are implemented using the iconv conversion tool.

Code tables

Code tables are text files with the following format: Three space-separated columns:

       Column #1 is the input char (in hex as 0xXX or 0xXXXX))
       Column #2 is the Unicode char (in hex as 0xXXXX)
       Column #3 the Unicode name

Most of the code tables are available at the Unicode Consortium: ftp://ftp.unicode.org/Public/MAPPINGS/

. Some of the code tables like samimac_roman and levi_winsam are composed from two code tables, the one that is used as input encoding and another that is used as the file was converted to utf-8.

       samimac_roman: codetables samimac.txt and ROMAN.txt
       levi_winsam: codetables levi.txt and CP1258.txt

levi.txt and samimac.txt are available under Trond’s home page at: smi-kodetabell.html. The codetables are composed using the function "combine_two_codings($coding1, $coding2, $outfile)" which is available in this package.

These encodings are available:

       latin6 => iso8859-10-1.txt
       plainroman => ROMAN.txt
       CP1258 => CP1258.txt
       iso_ir_197 => iso_ir_197.txt
       samimac_roman => samimac_roman.txt
       levi_winsam => levi_CP1258.txt
       8859-4 => 8859-4.txt
       winsam => winsam.txt

Guessing the input encoding

The original input encoding is guessed by examining the text and searching the most common characters. The unicode characters in hex are listed in hash %Char_Tables for North Saami for example. The uncommented characters are the ones that take part into guessing the encoding.

The encodings are listed in the hash %Charfiles, they are tested one at the time. The occurences of the selected characters in that encoding are counted and the one with most occurences is returned. There is a place for more statistical analysis, but this simple test worked for me.

If there is no certain amount of characters found, the test returns -1, which means that the characters should be already correctly utf-8 encoded. Or, the encoding was not found from the code tables.

INSTALL

To your own computer: copy the directory gt/script/samiChar to /System/Library/Perl/5.8.6/. The module is now installed to victorio.

Web upload interface

The main page of the web upload interface is http://www.divvun.no/upload/upload_corpus_file.html

The source of the page can be found in directory xtdoc/sd/src/documentation/content/xdocs/upload/. There are two cgi-scripts involved in the upload, upload.cgi and xsl-process.cgi. They are both in gt/script/cgi-scripts/ -catalog. upload.cgi uploads the file the user has selected, converts it to xml and prints out the metainformation form. The xsl-process.cgi handles the metainformation form and stores the contents of the fields to the file-specific xsl-file. The xml-file is converted once more with the updated metainformation.

All the files remain in the corp/tmp -directory. Every succeeded upload triggers an email message to the maintainer, who has to move the files manually to their place. The email notification is send as well if there is an error during the upload.

The file names are changed to secure ones and orig-hierarchy is checked for a file with the same content.

Corpus DTD