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zim_to_corpus

Scripts to extract the text from (mostly) Wikipedia pages from .zim archives. The repository contains two components: zim_to_dir, a C++ program to extract pages from zim archives; and a number of Python scripts to process its output and convert the data into various formats (such as inputs for BERT, fasttext, etc).

zim_to_dir

zim_to_dir is a C++ program that reads a Wikipedia .zim file and extracts all valid articles in it to files in a(n existing or newly created) directory. For now, it only works for Wikipedia dumps downloaded from the Kiwix archives.

An article is deemed valid if it is

  • in the article namespace (A)
  • not marked as deleted
  • not a redirect
  • not a disambiguation page

Suppored languages

As of now, only English and Hungarian dumps are supported. However, "support" for other languages can be added easily by modifying a very obvious line in zim_to_dir.cpp.

How to acquire

The zim_to_dir executable can be acquired in several ways:

  • Downloading a release from the zim_to_corpus repository
  • Building the docker image from the Dockerfile in the docker directory
  • Compiling the code manually

Usage

The executable

The executable has two main arguments: -i is used to specify the input .zim file, and -o the output directory. The rest of the arguments can be used to tune some of the aspects of the process; use the -h/--help option to list them. An example run:

zim_to_dir -i wikipedia_hu_all_mini.zim -o hu_mini/ -d 2000

One thing worth mentioning: the number of threads the program uses to parse records can be increased (from 4) to speed it up somewhat. However, since the zim format is sequential, the whole task is, to a large extent, I/O bound; because of this, the speed tops at a certain number of threads depending on the storage type: slow HDDs max out around 4 threads, while fast SSDs can scale even up to 24.

Docker image

The docker image can be used in two ways:

  1. The zim_to_dir executable can be copied out of a container and used as described above. For instance:
$ docker create zim_to_dir
e892d6ff245b55e03e41384d1e7d2838babd944a8e31096b3677a05359f38aba
$ docker cp e892d6ff245b:/zim_to_dir .
$ docker rm e892d6ff245b
e892d6ff245b
  1. The container is also runnable and will run zim_to_dir by default. However, in order for the container to see the input and output directories, they must be mounted as volumes:
docker run --rm --mount type=bind,source=/home/user/data/,target=/data zim_to_dir -i /data/wikipedia_hu_all_mini.zim -o /data/hu_mini/ -d 2000

Compiling the code

The script can be compiled with issuing the make command in the src directory. There are a few caveats, and because of this, it is easier to build the docker image, which compiles the source and all its dependencies:

cd docker
docker build -t zim_to_dir .

This method has the added benefit of not polluting the system with potentially unneeded libraries and packages and it also works without root access.

For those who wish to compile the code manually, here we present the general guidelines. Check out the Dockerfile for the detailed list of commands.

Compiler

Currently only g++ is supported and at least version 8 is required for proper C++17 support.

Libraries

The program requires a few libraries to work. Three of these (cxxopts, zstr and spdlog) are added as submodule to this repository. Make sure to clone it recursively (i.e.

git clone --recursive https://github.com/DavidNemeskey/zim_to_corpus

) or to activate the submodules after cloning normally:

git submodule init
git submodule update

Aside from these, two other libraries (and their sources or -dev packages) are required:

  1. zlib, for compression (e.g. zlib1g-dev in Ubuntu);
  2. libzim (also called Zimlib) to process the files. Libzim can be installed from the repositories of Linux distributions (libzim-dev), but e.g. Ubuntu only has version 4, so depending on how recent is the file to process, it might have to be compiled from source.

Note that some of the files in the Kiwix archives (most importantly, the English WP dump) require a fresh version of libzim. libzim version 6.3 is recommended; note that the API changed in 7.0, and zim_to_dir is not yet compatible with it.

Troubleshooting

Compilation fails because of article_index_type not found

You have an older version of libzim. Either upgrade it to version 4 or newer, or compile the code with -DARTICLE_SIZE_TYPE.

Invalid zim-file header

If zim_to_dir fails to read a zim file with the message "error reading zim-file header", then it was compiled against an outdated libzim version. Upgrade libzim to a more recent one. against is

extract_zim_htmls.py

Extracts all (Wikipedia, Project Gutenberg) HTMLs from the files output by zim_to_dir. Each page is cleaned up, filtered and converted into a minimal HTML, and then saved as a JSON string. In theory, this step could have been skipped, and the script that creates the final format(s) could have operated on the output of zim_to_dir. However, filtering substantially decreases the size of, and access time to, the data. This factor becomes important, as there are several output formats and the converter script might be called for all of them. Finally, the JSON-per-line format is ubiquitous, while the output of zim_to_dir is not.

Example usage converting the Wikipedia pages to simple HTML, retaining links and converting mathematical formulas to a placeholder symbol:

extract_zim_htmls.py -i hu_mini -o hu_json_htmls -t wikipedia -p '{"retain_tags": {"a": true}, "tag_replacements": {"math": "$MATH$"}, "delete_footnotes": true}' -P 4

filter_htmls.py

Filters documents and sections from the output of extract_zim_htmls.py.

Example usage:

filter_htmls.py -i hu_json_htmls -o hu_filtered_htmls -s skip_sections.lst -S skip_sections.regex -P 4

, where

  • skip_sections.regex contains one regex per line, such as ^Source, .* reading$
  • skip_sections.lst contains full section names on a line such as Notes

See section_statistics.py, below.

convert.py

Converts documents (Wikipedia pages, Project Gutenberg books, etc.) in the "simple HTML" format (i.e. the output of extract_zim_htmls.py) to various other formats (WT-2, BERT, CoNLL-U tsv, etc.)

Various output formats are supported, each of which has its own set parameters. The same can be said of the supported tokenizers. The available parameters can be found in the zim_to_corpus.converters module and zim_to_corpus.tokenization package.

Usage example with converting the filtered htmls to tsv, tokenized with emtsv:

convert.py -i hu_filtered_htmls -o hu_tokenized_tsvs -u doc -f tsv -t "qun:http://localhost:5000" -P 4

Note that the paragraphs are sent to the tokenizers one-by-one. The tokenizer in emtsv exhibits abysmal performance in this use-case, taking more than a second to process a single page. Use with caution.

section_statistics.py

Collects statistics of each section title in the corpus. The output is a tsv file with the following columns:

  • section title
  • number of times it occurs in the corpus
  • the number of times it is "empty", i.e. it only contains lists
  • the "empty ratio": the quotient of the last two numbers
  • the sum of the positions of the section, counted from the read $--$ probably not a very useful metric
  • the average position of the section, counted from the rear. Sections such as Sources or References have typically a low average position

The resulting statistics can be used to generate section filtering lists for filter_htmls.py.