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Backend for Korp, Språkbanken's corpus search tool
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Korp Backend

This is the backend for Korp, a corpus search tool developed by Språkbanken at the University of Gothenburg, Sweden.

The code is distributed under the MIT license.

The Korp backend is a Python 3 WSGI application, acting as a wrapper for Corpus Workbench.


To use the basic features of the Korp backend you need the following:

To use the additional features such as the Word Picture you also need:

For optional caching you need:

Installing the required software

These instructions assume you are running a UNIX-like operating system (Linux, macOS, etc).

Corpus Workbench

You will need the latest beta version of CWB. Install by following these steps:

Check out the latest version of the source code using Subversion by running the following command in a terminal:

$ svn co cwb

Refer to the INSTALL text file for instructions on how to build and install on your system. The source code comes with a bunch of install scripts, so if you're lucky all you have to do is run one of them. For example:

$ sudo ./install-scripts/install-linux

Once CWB is installed, by default you will find it under /usr/local/cwb-X.X.X/bin (where X.X.X is the version number). Confirm that the installation was successful by running:

/usr/local/cwb-X.X.X/bin/cqp -v

CWB needs two directories for storing the corpora. One for the data, and one for the corpus registry. You may create these directories wherever you want, but from here on we will assume that you have created the following two:


Setting up the Python environment and requirements

Optionally you may set up a virtual Python environment:

$ python3 -m venv venv
$ source venv/bin/activate

Install the required Python modules using pip with the included requirements.txt.

$ pip3 install -r requirements.txt

Configuring Korp

Normally nothing needs to be changed in the file, and all configuration is done by editing The following variables need to be set:

    The absolute path to the CQP binary. By default /usr/local/cwb-X.X.X/bin/cqp

    The absolute path to the cwb-scan-corpus binary. By default /usr/local/cwb-X.X.X/cwb-scan-corpus

    The absolute path to the CWB registry files. This is the /corpora/registry folder you created before.

If you are planning on using functionality dependent on a database, you also need to set the following variables:

    The name of the MySQL database where the corpus data will be stored.

    Username and password for accessing the database.

For caching to work you need to specify both a cache directory (CACHE_DIR) and a list of Memcached servers or sockets (MEMCACHED_SERVERS).

Running the backend

To run the backend, simply run


The backend should then be reachable in your web browser on the port you configured in, for example http://localhost:1234.

During development or while testing your configuration, use the flag dev for automatic reloading.

python3 dev

For deployment, Gunicorn works well.

gunicorn --worker-class gevent --bind --workers 4 --max-requests 250 --limit-request-line 0 korp:app

Cache management

Most caching is done using Memcached, except for CWB query results which are temporarily saved to disk to speed up KWIC pagination. While Memcached handles removing old cache by itself, you will still have to tell it to invalidate parts of the cache when one or more corpora are updated or added. This, and cleaning up the disk cache, is easily done by accessing the /cache endpoint. It might be a good idea to set up a cronjob or similar to regularly do this, making the cache maintenance fully automatic.

API documentation

The API documentation is available by accessing the backend without any arguments, or in docs/

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