The Public Domain Calculator is a project developed by students of FU Berlin. It is a service which is able to determine if an artistic or literary work is likely to be in the public domain.
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DDB Public Domain Calculator

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The DDB Public Domain Calculator (or DDB-PDC in short) is a service which, based on the the database of the Deutsche Digitale Bibliothek, is able to determine if an artistic or literary work is likely to be in the public domain. It consists of two parts:

  • A backend service which provides a REST API for calculating the public-domain status of any work in the DDB.

  • A Drupal module which allows querying the public domain calculator through a simple web interface.

Installation and Setup

The following sections describe how to set up both the DDB-PDC backend and Drupal module on a server. Both were mainly tested on Ubuntu Server, but are likely to work on any other Unix-based system.


Installing and running the DDB-PDC backend requires the following:

  • An API key for access to the Deutsche Digitable Bibliothek API. See the DDB API documentation for instructions.

  • Java 7 or newer (both OpenJDK and the Oracle Java work). For being able to build the code, install the full JDK. Maven is also required for building. On Ubuntu, you can use the following command for installing:

    sudo apt-get install openjdk-7-jdk maven

    On OS X, the easiest way to install Maven is with Homebrew:

    brew install maven
  • MongoDB if you want to use the PDC result database (see Configuring the PDC Result Database). This is entirely optional.

    # Ubuntu
    sudo apt-get install mongodb-server
    # OS X + Homebrew
    brew install mongodb

The Drupal module needs Drupal 7 or higher; see the Drupal Installation Guide for setup instructions.

Building the Backend

After cloning this repository, move to its root folder and run

mvn install

This will compile the DDB-PDC backend, test it, and finally create an executable JAR file named ddb-pdc-<version>.jar in the target/ sub-directory. You can copy it anywhere you want, e.g.:

mkdir -p /opt/ddb-pdc
cp target/ddb-pdc-<version>.jar /opt/ddb-pdc/ddb-pdc.jar

Configuring the Backend

Configuration of the DDB-PDC backend is done in the file, which can be found in config/. When running the backend, this file must be either in the current working directory or in the config/ sub-directory thereof. The easiest approach is to copy into the same folder as the backend JAR file.

You can pretty much leave the default configuration as-is. However, you do need to fill out the ddb.apikey option, which tells the backend which API key to use for accessing the DDB API:


Configuring the PDC Result Database

Optionally, you can configure the backend to save the result of every public-domain calculation - including a trace explaining why a work was considered public-domain or not - to a MongoDB database. If the same work is queried afterwards, the backend will serve the result directly from the database instead of hitting the DDB API and re-calculating the public-domain status. (If the stored result is outdated because it is from an earlier year, it is re-calculated anyway.)

This feature doesn't only speed up multiple public-domain calculation requests for the same work, but also makes it possible to do further processing on the collected results in the future, for instance to generate reports.

To enable the result database, set in and configure the database connection parameters:

Running the Backend

To start the backend server, simply run the JAR file with java -jar:

cd /opt/ddb-pdc
java -jar ddb-pdc.jar

Make sure that you are in the directory containing (or config/ when you run the command. The backend will now listen for HTTP requests on the port configured through the server.port option (8080 by default).

For Ubuntu, this repository contains a Upstart job file that lets you run the backend as a background service. Simply copy extras/ddb-pdc.conf to /etc/init and adapt it to suit your needs. After this is done, you can control the backend server like any other Upstart job:

sudo start ddb-pdc
sudo restart ddb-pdc
sudo stop ddb-pdc

Installing the Drupal Module

The Drupal module is contained in drupal/ddb_pdc/. To install it, copy the directory to sites/all/modules or sites/<your_site>/modules/ in your Drupal installation. An accompanying example theme is available in drupal/ddb_fuberlin/ and can be installed by copying it to sites/all/themes/ or sites/<your_site>/themes/. After that, enable everything through the Drupal admin controls as usual.

The ddb_pdc module needs to know where to find the backend service. By default, it looks for it at http://localhost:8000. To change this URL in the module's configuration.


The backend service is a Java-based Spring Boot application. See the Spring Boot Manual for more information about the general structure of Spring Boot projects and the available Maven goals. Below is a quick overview of the most common commands.


The backend is accompanied by a suite of unit and integration tests based on JUnit. To run them, execute

mvn test

Running mvn verify will also generate a code coverage report with JaCoCo and save it to target/site/jacoco/.

By default, the tests for the PDC result database are skipped so that running the test suite doesn't require a running MongoDB. To enable them, set to true in


You can run the backend server from the command line during development with

mvn spring-boot:run

The configuration in config/ will be used. Of course, you can also run the server from your IDE as normal (the main class is de.ddb.pdc.Main).

Coding Style

All code is written according the Google Java Style Guide. To enforce this, a matching Checkstyle configuration is included in this repository. To check the code for style violations, run

mvn checkstyle:checkstyle