Common Voice Sentence Extractor

Common Voice is Mozilla's initiative to help teach machines how real people speak. For this we need to collect sentences that people can read out aloud on the website. Individual sentences can be submitted through the Sentence Collector. This only can scale so far, so we also use automated tools to extract sentences from other sources.

Right now this tool supports extractions from the following sources:

• Wikipedia - max 3 sentences per articles

For a source to be added, the dataset needs to be vetted by Mozilla to check license compatibility. If you know about a good source, please start a topic on Discourse. Once it's been verified that a source can be used, check the "Adding another scrape target" further below.

Setup

• Rust Nightly (follow the instructions and customize the install to select the nightly channel)

Note: as long as we're using the current punkt dependency, we need to use the Nightly version of Rust.

Clone this repo:

git clone https://github.com/Common-Voice/cv-sentence-extractor.git

Wikipedia Extraction

You need to download the WikiExtractor:

git clone https://github.com/attardi/wikiextractor.git

Extraction

Extract Wikipedia

We can only extract at most 3 sentences per article.

1. Download the latest Wikipedia dataset backup dump from Wikimedia, select the one with pages-articles-multistream in its name.

Example (you can change "en" to your locale code)

wget https://dumps.wikimedia.org/enwiki/latest/enwiki-latest-pages-articles-multistream.xml.bz2
bzip2 -d enwiki-latest-pages-articles-multistream.xml.bz2

2. Use WikiExtractor to extract a dump (this might take a few hours)

cd wikiextractor
python WikiExtractor.py --json ../enwiki-latest-pages-articles-multistream.xml

Important note: Please check the section about creating a rules file and a blocklist at this point, you might want to consider creating them and that process should happen before step 3.

3. Scrape the sentences into a new file from the WikiExtractor output dir (this might take more than 6h to finish)

cd ../cv-sentence-extractor
cargo run -- extract -l en -d ../wikiextractor/text/ >> wiki.en.txt

Tip: You don't need this last process to finish to start observing the output, wiki.en.txt should get a few thousands sentences in just a few minutes, and you can use that as a way to estimate the quality of the output early on and stop the process if you are not happy.

Using language rules

The following rules can be configured per language. Add a <language>.toml file in the rules directory to enable a new locale.

Name	Description	Values	Default
abbreviation_patterns	Rust regex defining abbreviations	Rust Regex Array	all abbreviations allowed
allowed_symbols_regex	Regex of allowed symbols or letters. Each character gets matched against this pattern.	String Array	not used
broken_whitespace	Array of broken whitespaces. This could for example disallow two spaces following each other	String Array	all types of whitespaces allowed
disallowed_symbols	Array of disallowed symbols or letters. Only used when allowed_symbols_regex is not set or is an empty String.	String Array	all symbols allowed
disallowed_words	Array of disallowed words	String Array	all words allowed
even_symbols	Symbols that always need an event count	Char Array	[]
matching_symbols	Symbols that map to another	Array of matching configurations: each configuration is an Array of two values: ["match", "match"]. See example below.	[]
max_word_count	Maximum number of words in a sentence	integer	14
may_end_with_colon	If a sentence can end with a : or not	boolean	false
min_characters	Minimum of character occurrences	integer	0
min_trimmed_length	Minimum length of string after trimming	integer	3
min_word_count	Minimum number of words in a sentence	integer	1
needs_letter_start	If a sentence needs to start with a letter	boolean	true
needs_punctuation_end	If a sentence needs to end with a punctuation	boolean	false
needs_uppercase_start	If a sentence needs to start with an uppercase	boolean	false
other_patterns	Rust regex to disallow anything else	Rust Regex Array	all other patterns allowed
quote_start_with_letter	If a quote needs to start with a letter	boolean	true
replacements	Replaces abbreviations or other words according to configuration	Array of replacement configurations: each configuration is an Array of two values: ["search", "replacement"]. See example below.	nothing gets replaced

Example for matching_symbols

matching_symbols = [
  ["„", "“"],
  ["(", ")"],
  ["[", "]"]
]

This matches all occurrence of „ with “, all occurrence of ( with ), all occurrence of [ with ].

Input: This is „a test“ and (another one)
Output: Valid

Input: This is (a test))
Output: Invalid

Example for replacements

replacements = [
  ["test", "hi"],
  ["etc.", "et cetera"],
  ["foo", ""],
]

This replaces all occurrence of test with hi, all occurrence of etc. with et cetera, and removes all foo.

Input: I am a test etc.
Output: I am a hi et cetera

Input: I am foo test a test
Output: I am hi a hi

Using disallowed words

In order to increase the quality of the final output, you might want to consider filtering out some words that are complex, too long or non-native.

You can do this by adding these words to the language rules file for your language under the disallowed_words setting.

If your list is too long, you can also place a <language>.txt file in the rules/disallowed_words directory to enable a new locale. Each word should be on a new line.

Create a blocklist based on less common words

You can create a solid blocklist by generating a list of the less common words from your Wikipedia.

To do so, first you should create a full export with all Wikipedia sentences. Note that all processes below will take a while to execute.

After running step 1 and 2 from the Usage section above, run:

cd ../cv-sentence-extractor
cargo run -- extract -l en -d ../wikiextractor/text/ --no_check >> wiki.en.all.txt

Then you can use the cvtools scripts to generate a list of the word frequency:

cd  ..
git clone https://github.com/dabinat/cvtools/
cd cvtools
python3 ./word_usage.py -i ../cv-sentence-extractor/wiki.en.all.txt >> word_usage.en.txt

You will have to read the word_usage.en.txt file to decide where you should put the limit. Usually words with less than 80-60 repetitions are bad.

grep -i "80" ./word_usage.en.txt

Once you know the frequency limit, you can generate your blocklist by running:

python3 ./word_usage.py -i ../cv-sentence-extractor/wiki.en.all.txt --max-frequency 80 --show-words-only >> ../cv-sentence-extractor/src/rules/disallowed_words/en.txt

You can use also --strip-by-apostrophe which is handy for languages using ' in their sentences to recognize more words.

When you run the scrapping in step 2 from the Usage section this list will automatically be used if present.

Getting your rules/blocklist incorporated

In order to get your language rules and blocklist incorporated in this repo, you will need to create a Pull Request explaining the following:

• How many sentences did you get at the end?
• How did you create the blocklist file?
• Get at least 3 different native speakers (ideally linguistics) to review a random sample of 100-500 sentences and estimate the average error ratio and comment (or link their comment) in the PR.

Once we have your rules into the repo, we will be able to run the extraction from our side and incorporate the sentences into the Common Voice repo. But please take note that we have limited resources and we can't guarantee a specific date for us to run this process (we are looking into automating it).

Adding another scrape target

If you find a new open data source that provides a lot of sentences (Example), we suggest to not go through through the Sentence Collector but rather adding a scrape target here. Before you do so, let's discuss it on Discourse first!

• In app.rs, add a new extraction command - same arguments as the extract task, but with a better - more descriptive - name identifying your data source
• In loader.rs write your own loader according to the data structure - the data structure should be fairly simple, you might need to consider writing a separate script to fetch and prepare the sentences first (as we do with the WikiExtractor for Wikipedia)
• In app.rs add a new else if in the start function to generate your config and start the extraction, passing your own custom loader you wrote

Automatic extraction

Currently the following data sources are available for automatic extraction:

• Wikipedia

On every Pull Request

On every PR we will trigger a sample sentence extraction which can be used for verification.

On pushes to master

On every push to master, we will run a full sentence extraction on the specified language if the commit message includes --full-wiki-extraction=<language> at the end of the message.

Manual trigger

Jobs can be triggered manually by adding a comment to an issue or Pull Request.

/action [job] [language] [otherParams]

• job: name of the job to run, this can be any of: extract, blocklist, and whatever new sources will use as "subcommand"
• language: language code to process for: en, de, ...
• otherParams: any other params needed depending on the job

The job will then add a comment with its URL, so you can check the output and download the files you need.

Extracting from Wikipedia - English

/action extract en

Create a blocklist for English - 80 occurrences threshold

/action blocklist en 80