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The Distance Machine

The Distance Machine is a Web-based tool that finds words in a text that are uncommon in texts from a given year. This Git repository includes both the source code for this Web application (written in an Ajaxy way with JavaScript and PHP) and some scripts that were used to create the data underlying it. The tool relies on a statistical model for determining when words come into or go out of common usage, and this model may be useful for other applications.

The Distance Machine is under the MIT license. This package incorporates D3 3.4.8, jQuery 1.10.2, jQuery UI 1.10.4, jQuery UI Touch Punch, and the jQuery cookie and watermark modules. D3 is under the BSD license; the other packages are all available under the MIT license.

The Word Count Data

In order to determine when words come in and go out of common usage, this tool needs information about how frequently each word in the language was used in each year. The live version of the program does this using data based on Google Books and EEBO-TCP.

The script is used to load the 1-grams data from Google (available here) into a MySQL database. It is designed to work with the 2012 version of the 1-grams and total_counts files. This script might also be useful if you are attempting to load the data into MySQL for other applications. For this script to work, you will need to set up a MySQL database using "usage.sql", and then modify the code so that it has the correct MySQL connection information.

You do not necessarily need to use the data from Google Books; the rest of the system will work with any data in the appropriate format. The source code also includes scripts for loading data from either plain text or TEI-encoded corpora. To load word counts from a plain-text corpus, use; if the corpus is in TEI format, use the script beforehand to convert it to plain text. This is the method used to load the EEBO-TCP corpus.

In some versions of MySQL, it is necessary to mess around with the text encoding and collation settings to ensure that accented characters are handled correctly. If things are working right, you will get different results for these two queries:

SELECT * FROM count WHERE word = 'tree';

SELECT * FROM count WHERE word = 'trée';

The Usage Period Model

Based on the yearly word counts, we need to determine the periods in which each word was in use. This is done using a two-state hidden Markov model, which we compute using the Viterbi algorithm. This happens in the script, which goes through every single word in the word count data set, computes the model, and deposits the results in the usage_periods table. For each word, this table will contain a string representing the periods in which that word was in common use, separated by semicolons (e.g. "1810-1840;1952-"). By default, this script will only look at data going back to 1750, because before then the number of books printed is so small that the statistics are unstable. You can change this by modifying the source code.

Since this script can take a very long time to run on an ordinary computer (on the order of weeks, even on a high-end workstation), I have included the results in the file usage_periods.txt.gz. This file includes the usage periods for every word in the US and UK English data sets from Google in a format that can be loaded directly into the usage_periods table in MySQL.

If you just want to work with the usage period algorithm, you can stop here; however, if you want to get the Distance Machine Web application working, you will need to do a few more things.

The Processed Data

Further processing is needed to get the data into an efficient format for the Web interface to work with. This is done with the script, which converts the usage periods from a human-readable format (e.g. "1851-1910") to a format from which the status of a word in any given year can be determined with a regular expression search (in that case, "n18lxn1850o1911o1912o1913o1914o191ro192xo193xo194xo19rx"). Each 5-character sequence in this string represents a period in which a word is either more common later (indicated with first character "n" for "new"), more common earlier ("o" for "old"), or more common both earlier and later ("l" for "lapsed"). The remaining four characters represent either a year, a decade ("192x"), a half-decade ("192l" for 1920-1924 or "192r" for 1925-1929), a century ("18xx"), or a half-century ("18lx" for 1800-1849 or "18rx" for 1850-1899). The reason for this complex representation is that the JavaScript frontend needs to figure out which words to highlight near-instantaneously in order for the slider to be responsive. Inelegant as this format is, it proved to be far more efficient than any alternative I could devise.

Finally, the application uses a cache of the data for a list of very common words, which is generated with the script. The resulting file (named "CACHE") needs to be stored on the server in a location accessible by the Web server. If you are using data for a language other than English, you should alter this script to use a different list of words.

WordNet and Other Dictionaries

The Web application uses a copy of WordNet to provide definitions of words. You can use these scripts to load the WordNet data into MySQL.

It is possible to include other dictionaries by loading them into the dict table in MySQL and listing them in the config.php and config.js files. Headwords should be in lowercase.

The Web Application

In order to get the Web application running, you will need to load the MySQL data as described above, and then you will need to set up a few things on the server. The application needs two directories in which to store the texts that users upload (a temporary storage location for unsaved texts and a permanent one for saved texts); it also needs access to the CACHE file and a lockfile to prevent operations from interfering with one another. You will need to modify config.php to specify the MySQL credentials and the locations of these resources. If you are using a different data set from the default one (e.g. different time period limits or different languages), you should also modify config.js and config.php accordingly. You will, finally, need to set up URL aliases as indicated in the htaccess file and create a cronjob to remove unused texts (see the "crontab" file in the database directory).

The admin_tools directory contains some scripts that are useful in monitoring the usage of the site. If you want them to work, you will need to alter connection.php with the correct MySQL credentials. These scripts will need to be run under a user account that has access to the directories where texts are stored. There is also a Web-accessible interface to most of these tools available in the public_html/admin directory. You will probably want to password-protect this directory if you include it.

Archive Mode

In addition to providing an interface in which the user can enter their own texts, the Distance Machine can be used to host an already-prepared collection of texts. When this is set up, there will be a search interface that the user can use to find texts. The search interface provides some handy features that are not always part of search engines. The search box includes a visualization that shows the frequency of each search term over time, which can be useful in determining whether you need to account for language change. The list of search results includes excerpts showing the first few instances of the search terms in each text, with context on both sides. When you click through into a text, you get all of the Distance Machine features for highlighting words, plus a feature that makes it easy to jump to the specific parts of the text where search terms occur. This functionality is experimental at the moment; it is not guaranteed to be scalable and the user interface is not ideal.

To set this up, you will need to enable archive mode in the config.php file. You will also have to create the archive directory, which will contain the annotated versions of the texts, and the MySQL tables defined in archive/archive.sql, which will contain plain-text versions that are indexed for search. You should then compute the word count and usage period data for your collection, as described above. You will also need a file containing some metadata, such as the publication years, titles, and authors. If you are building your archive based on TEI-encoded texts you can extract this information automatically using archive/

Once this is all ready, create a directory within the base archive directory with the same name as your corpus; this will be where you put the processed files. Then run the script archive/create_archive.php to populate both this directory and the MySQL table by processing a plain-text version of your corpus. Finally, add the additional Apache rewrite rules stored in archive/htaccess. Once this is all done, you should be able to access the search engine by opening /archive//search in your Web browser.


A Web-based tool for identifying words in a text that were unusual at a given point in time







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