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Kurator-Akka Framework

The kurator-akka repository hosts source code for the Kurator-Akka workflow engine component of the Kurator workflow automation toolkit. This software toolkit is being developed as part of the Kurator project and is designed to make it easy to develop and run high-performance data cleaning workflows.

Kurator-Akka is based on the Akka actor toolkit and runtime. It aims to accelerate development of new data cleaning actors and to facilitate development of new workflows assembled from these actors. Kurator-Akka supports actors implemented either in Java or Python, and the framework shields actor developers from the complexities of using the Akka API directly. Workflows are specified using a YAML-based language that defines how data flows between the actors at run time.

The remainder of this README provides simple examples of actors and workflows that employ Kurator-Akka, describes how to run example workflows at the command line, and outlines the setup required to develop with or extend the Kurator-Akka source code. Detailed user documentation will be provided elsewhere.

The TDWG 2015 presentation Data cleaning with the Kurator toolkit provides an overview of the Kurator project and tools described in this README. Also see the list of publications on the Kurator project wiki.

Citing Kurator-Akka


Obtaining Kurator-Akka

An executable jar is available in the current release

Also see the Kurator-Web application for running Kurator-Akka workflows through a web interface.

Kurator-Akka is available as a dependency in maven central:


Example actor and workflow

A workflow is a collection of actors configured to carry out some set of tasks. An actor is a software component that receives data either from outside the workflow, or from other actors within the same workflow; and either communicates the results of its computations to other actors, or saves the results outside the running workflow. Actors in a Kurator-Akka workflow run concurrently in different threads.

Kurator-Akka simplifies use of the underlying Akka actor framework by providing the KuratorActor class as an alternative to Akka's UntypedActor class. A sub-class of UntypedActor, KuratorActor makes scientific-workflow specific capabilities available to actor and workflow authors, most critically through the onData() event handling method. When Akka triggers events handled by the UntypedActor.onRecieve() method, the KuratorActor implementation of onRecieve() makes calls to the onData() methods defined by Kurator-Akka actors. Kurator-Akka further provides automated means for orchestrating actors in ways compatible with computational pipelines typically used to automate scientific workflows. For example, Kurator-Akka correctly times actor initialization and actor shutdown events so that workflow authors need not concern themselves with these otherwise complex--yet critical--workflow management details.

Actors in Kurator-Akka may be implemented either in Java or in Python.

Java implementation of a Multiplier actor

The Java class below defines a simple actor for multiplying an integer by a configurable constant:

import org.kurator.akka.KuratorActor;

public class Multiplier extends KuratorActor {
    public double factor = 1;
    @Override public void onData(Object i) {
    	broadcast((double)i * factor);

As shown above, a new Java actor can be implemented by declaring a new Java class that overrides the onData() method of the org.kurator.akka.KuratorActor base class. This method will be called by the Kurator-Akka framework each time the actor receives any data. The call to broadcast() within the onData() method sends data (usually the results of performing some computation on the data received by the actor) to any other actors in the workflow configured to listen to this one.

An alternative approach to defining a Kurator-Akka Java actor is to implement the actor as a Plain Old Java Object (POJO) and declare to the Kurator-Akka framework which public method is to be called for each received data object. By default the method named onData() will be used. This method must be a function that returns the value to be broadcast to other actors. A POJO implementation of the above Multiplier actor is as follows:

public class Multiplier {
    public double factor = 1;
    public void multiply(Object i) {
    	return((double)i * factor);

No class inheritance is required when using using the POJO approach. However, POJO actors have the limitation that only one output data item may be returned and communicated to other actors for each input data item the actor receives. In contrast, Java actors derived from org.kurator.akka.KuratorActor may call the broadcast() method multiple times within the onData() method and so produce multiple outputs per input.

Both approaches for Java actors support event handlers in addition to onData(). These include onInitialize(), called before any actor produces output; onStart(), which allows actors to produce output data before any input data is received; and onEnd(), which is called after an actor has handled the last data item it will receive during a workflow run.

Python implementations of the Multiplier actor

An implementation of the same actor in Python is analogous to the POJO approach above, with the difference that the input data handler can, but does not need to be, defined as a method in a class. Any name may be used for the input data handing function; on_data() is assumed by default.

Thus, the following Python snippet can serve as a valid actor implementaion:

factor = 1
def multiply(i):
    return factor * i

And methods defined in Python classes work as well:

class MultiplierActor(object):
    def __init__(self):
        self.factor = 1
    def multiply(i):
        return self.factor * i

As for POJOs, the Kurator-Akka framework can be configured to call the multiply() function on each data item received by either of the above implementations of the actor. The value returned from the function is automatically broadcast to listeners. Unlike POJO actors, actors implemented as Python functions alternatively may produce a sequence of output data items for each input data item received by using the yield keyword instead of return.

Similar to Java actors, Python actors may provide on_initialize(), on_start(), and on_end() event handlers (and may name these functions arbitrarily).

YAML declaration of a Python implementation of the Multiplier actor

In addition to the Java or Python definition of an actor, an actor type declaration authored in YAML is needed to make the actor available for use in workflows. The following declares that actors of type Multiplier, a subtype of PythonActor, invoke the multiply() function defined in the file to handle incoming data:

- id: Multiplier
  type: PythonActor
    onData: multiply

The argument to the script: property is an absolute path to the Python file defining the function, or a path relative to the directory in which the workflow is invoked. A less fragile way of defining a Python actor is to make the Python script part of a Python package, and use the module property to refer to the script. For example, if is in the math.operators package, then the following declaration will work:

- id: Multiplier
  type: PythonActor
    module: math.operators.multiplier
    onData: multiply

A declaration corresponding to a Python class implementation of the actor defined in a math.actors package would be as follows:

- id: Multiplier
  type: PythonClassActor
    pythonClass: math.actors.MultiplierActor
    onData: multiply

Analogous declarations must be provided for Java actors as well.

Defining a workflow that uses the Multiplier actor

With either of the above YAML snippets saved to a file named actors.yaml, the Python-based Multiplier actor can be used in a workflow also defined in YAML. The workflow below accepts an input value from the user, multiplies it by 3, and outputs the result:


- file:actors.yaml


- id: MultiplyByThreeWorkflow
  type: Workflow
      - !ref ReadOneNumber
      - !ref MultiplyByThree
      - !ref PrintProduct

- id: ReadOneNumber
  type: NumReader

- id: MultiplyByThree
  type: Multiplier
      - !ref ReadOneNumber
      factor: 3

- id: PrintProduct
  type: NumPrinter
      - !ref MultiplyByThree

The above declaration states the following: MultiplyByThreeWorkflow is a workflow comprising three actors, ReadOneNumber, MultiplyByThree, and PrintProduct. MultiplyByThree listens to (receives its input from) ReadOneNumber, and PrintProduct receives its input in turn from MultiplyByThree. MultiplyByThree is declared to be an instance of the Multiplier actor type defined previously; this instance of Multiplier is configured to multiply each value it receives by a factor of 3. The YAML declarations for the underlying actor types NumReader, Multiplier, and NumPrinter are all imported from actors.yaml.

The YAML definition of a workflow using Java implementations of each actor looks identical to a workflow using Python actors. Java actors and Python actors can be used together in the same workflow.

Inlining Python actors

Kurator-Akka allows the code for Python actors to be provided inline, i.e. within the workflow definition itself. No additional Python script file or YAML actor type declaration is needed in this case (the type of the actor is simply PythonActor). For example, the block of YAML defining the MultiplyByThree actor in the workflow definition above depends on an additional YAML declaration for the Multiplier actor defined in the actors.yaml file, which in turn depends on a Python script file named Because the code for this actor is only a few lines long, it may be reasonable to define the actor entirely inline. In other words, this block of YAML in the workflow:

- id: MultiplyByThree
  type: Multiplier
      - !ref ReadOneNumber
      factor: 3

can be replaced with:

- id: MultiplyByThree
  type: PythonActor
      - !ref ReadOneNumber
    onData: triple
    code: |
      def triple(n):
        return 3 * n

The Python code defining the multiply() function is now defined within the same YAML file that declares the workflow as a whole. Inlined Python actors are useful for implementing simple actors needed for specific workflows.

Preparing to run Kurator-Akka

This section describes how to set up an environment for writing your own actors and workflows, and executing them using Kurator-Akka. Instructions for building and extending the Kurator-Akka framework itself are provided following this section.

Check installed version of Java

Kurator-Akka requires Java version 1.8.0 or higher. To determine the version of java installed on your computer use the -version option to the java command. For example,

$ java -version
java version "1.8.0_65"
Java(TM) SE Runtime Environment (build 1.8.0_65-b17)
Java HotSpot(TM) 64-Bit Server VM (build 25.65-b01, mixed mode)

Instructions for installing Java may be found at If you plan to develop new actors in Java (not just in Python) be sure to install the JDK. Otherwise a JRE is sufficient.

Download the Kurator-Akka jar

Kurator-Akka is distributed as an executable jar (Java archive) file that can be invoked using the java -jar command. To download the most recent build of the latest Kurator-Akka code, navigate to the Latest Release and click on the kurator-akka-1.0.1-jar-with-dependencies.jar link under the Assets tab to download the executable jar artifact for the kurator-akka job.

Install Kurator-Akka on your system

Once you have downloaded the Kurator-Akka jar, save the file in a convenient location and rename it to something like kurator-akka.jar. Kurator-Akka can now be run using the java -jar command. The jar file includes several sample workflow scripts which can be accessed from the command line.

Test your installation by running the hello.yaml workflow. Assuming kurator-akka.jar is in your current working directory type:

java -jar kurator-akka.jar -f classpath:/org/kurator/akka/samples/hello.yaml

If the Kurator-Akka jar is stored elsewhere, qualify kurator-akka.jar with the path to that file. For example, if you stored the jar file in the bin subdirectory of your home directory, running Kurator-Akka would look something like this on Linux or OS X:

$ java -jar ~/bin/kurator-akka.jar -f classpath:/org/kurator/akka/samples/hello.yaml
Hello World!

On Windows platforms the command is similar:

$ java -jar %USERPROFILE%\bin\kurator-akka.jar -f classpath:/org/kurator/akka/samples/hello.yaml
Hello World!

Define a short command for running Kurator-Akka at the prompt

If you are running Kurator-Akka on an Apple OSX or Linux system (or use Git Bash or Cygwin on Windows), you may define an alias to simplify running Kurator-Akka at the command line. On Windows platforms you similarly may define a doskey macro for running Kurator-Akka at the prompt.

For example, if you have saved kurator-akka.jar to the bin subdirectory of your home directory, the following command will create a bash alias for running Kurator-Akka simply by typing ka:

alias ka='java -jar ~/bin/kurator-akka.jar'

If you use csh or tcsh the command is:

alias kurator-akka java -jar ~/bin/kurator-akka.jar

On Windows the command to create the ka doskey macro is:

 doskey ka=java -jar %USERPROFILE%\bin\kurator-akka.jar $*

On all platforms the hello.yaml demo now can be run using the short command:

$ ka -f classpath:/org/kurator/akka/samples/hello.yaml
Hello World!

Extract and run sample workflows (optional)

If you would like to browse and edit the sample workflows included in the Kurator-Akka jar, type the following (qualifying the path to kurator-akka.jar as necessary) to extract its contents to your filesystem:

jar xf kurator-akka.jar org/kurator/akka/samples

To run a script residing on the filesystem, you can use the file: qualifier instead of classpath::

$ java -jar kurator-akka.jar -f file:org/kurator/akka/samples/hello.yaml
Hello World!

The file: qualifier is optional, however. By default Kurator-Akka looks for workflows on your filesystem. So this will work, too:

$ java -jar kurator-akka.jar -f org/kurator/akka/samples/hello.yaml
Hello World!

Note that the path to hello.yaml above is relative (it does not start with a /).

Developing new Java actors

New Java actors can be implemented using standard Java development tools. Simply make sure that the kurator-akka.jar file is on the CLASSPATH when compiling your actors, and that the compiled .class files are on the CLASSPATH when running Kurator-Akka.

For example, if your new actor is defined in the file, and kurator-akka.jar is stored in ~/bin, the following command will compile your actor to produce MyActor.class:

javac -classpath ~/bin/kurator-akka.jar

Note that including kurator-akka.jar on the classpath during compilation is unnecessary if your actor is a POJO, i.e. not a subclass of org.kurator.akka.KuratorActor.

Developing new Python actors

New Python actors can be used in Kurator-Akka workflows without any manual compilation step. Python actors that depend only on packages provided as part of a standard Python distribution can be developed without any preparation other than downloading the Kurator-Akka jar file. The kurator-akka.jar also includes within it all of the 3rd-party Python packages requierd by the basic actors provided in the jar.

However, if you develop new Python actors that depend on 3rd-party packages not included in the Kurator-Akka jar file, you will need to install these packages to a local Jython installation. Jython is a Java implementation of the Python language and runtime, and comes with the same package management tools as Python, including pip.

Install the Jython 2.7.1b3 distribution to support 3rd party Python packages

  • Download the Jython 2.7.1.b3 installer jar. The downloaded jar file will be named jython_installer-2.7.1b3.jar.

  • The Jython installer can be started either by double-clicking the downloaded jar file (on Windows or OS X) or executing the downloaded jar at the command prompt using the java -jar command:

      java -jar jython_installer-2.7.1b3.jar
  • Note the location of the Jython installation directory created by the installer.

Install dependencies for native actor support

As an alternative to the actors that used the Java based Python interpreter Jython, native actor support is provided for embedded Python and R.

On Linux, install the native dependencies for R and Python via:

sudo apt-get install r-base python python-dev

On MacOS, install the native dependencies via:

brew install python r

Make installed Python packages available to Kurator

Define the environment variable JYTHONHOME to indicate the path to the newly installed Jython 2.7.0 distribution. Kurator-Akka uses this variable to locate 3rd-party Python packages that specific actors depend upon.

In a bash shell the environment variable can be assigned with the following command (assuming, for example, that Jython was installed to the jython2.7.1b3 directory within your home directory):

export JYTHONHOME=$HOME/jython2.7.1b3/

On Windows it is easiest to define the variable using the Advanced system settings Environment Variables dialog:

Control Panel -> System -> Advanced system settings -> Advanced -> Environment Variables

Kurator-Akka now will have access to all Python packages installed to your Jython installation. Jython 2.7 includes the pip tool (in the bin subdirectory of the Jython installation) which makes it easy to install 3rd-party Python packages and to install their dependencies automatically. For example, this following command installs the suds-jurko package which subsequently can be imported by Python actors:

$JYTHON_HOME/bin/pip install suds-jurko

Make your own Python code available to Kurator-Akka

To make your own Python code available to Kurator-Akka specify the directory (or directories) containing your Python packages using the JYTHONPATH variable. For example, if you have defined a Python function add_two_numbers() in a file named, and placed this Python module (file) in the $HOME/packages/math/operators directory, you can make your function available for use in an actor via the math.operators.adders module by defining JYTHONPATH to include the $HOME/packages/ directory and then declaring the module and onData properties of the actor as follows:

- id: Adder
  type: PythonClassActor
    module: math.operators.adders
    onData: add_two_numbers

Note that Python packages always require that a file named be present in each directory comprising the package. In the above example, the directories $HOME/packages/math and $HOME/packages/math/operators must each contain a file named These files may be empty.

For native actor support set the PYTHONPATH environment variable to the same value.

Instructions for Kurator-Akka workflow engine developers

If you would like to build, modify, or extend the Kurator-Akka workflow engine you may set up your development environment as follows.

JDK and Maven configuration

The Kurator-Akka framework is built using Maven 3. Before building Kurator-Akka confirm that the mvn command is in your path, that your version of Maven is at least 3.0.5, and that a JDK version 1.8.0 (or higher) is found by Maven:

$ mvn --version
Apache Maven 3.3.3 (7994120775791599e205a5524ec3e0dfe41d4a06; 2015-04-22T04:57:37-07:00)
Maven home: /Users/tmcphill/DropBox/Library/Java/apache-maven-3.3.3
Java version: 1.8.0_65, vendor: Oracle Corporation
Java home: /Library/Java/JavaVirtualMachines/jdk1.8.0_65.jdk/Contents/Home/jre
Default locale: en_US, platform encoding: UTF-8
OS name: "mac os x", version: "10.11.3", arch: "x86_64", family: "mac"

JDK 7 and Maven 3 downloads and detailed installation instructions can be found at the following links:

Project directory layout

Kurator-Akka adopts the default organization of source code, resources, and tests as defined by Maven. See for more information. The most important directories are listed below:

Directory Description
src/main/java Source code to be built and packaged for distribution.
src/main/resources Resource files to be packaged with production code.
src/test/java Source code for unit tests. Not included in packaged distributions.
src/test/resources Resource files available to tests. Not included in packaged distributions.
target Destination directory for packaged distributions (jar files) built by maven.
target/classes Compiled java classes for source code found under src/main/java.
target/test-classes Compiled java classes for test code found under src/test/java.
target/dependency Automatically resolved and downloaded dependencies (jars) that will be included in the standalone distribution.
target/apidocs/ Local build of Javadoc documentation.
packages Custom Python packages to be included in the distribution.

Note that the final directory, packages contains all of the Python source files developed and delivered with the Kurator-Akka engine. Any new packages added to this directory are automatically made available to Kurator-Akka.

Building and testing with maven

Kurator-Akka can be built and tested from the command line using the following commands:

Maven command Description
mvn clean Delete the target directory including all compiled classes.
mvn compile Download required dependencies and compile source code in src/main/java. Only those source files changes since the last compilation or clean are built.
mvn test Compile the classes in src/test/java and run all tests found therein. Peforms mvn compile first.
mvn package Package the compiled classes in target/classes and files found in src/main/resources in two jar files, kurator-akka-1.0.1-SNAPSHOT.jar and kurator-akka-1.0.1-SNAPSHOT-jar-with-dependencies.jar. The latter also contains all jar dependencies. Performs mvn compile and mvn test first, and will not perform packaging step if any tests fail. Use the -DskipTests option to bypass tests.
mvn javadoc:javadoc Build Javadoc documentation. The mvn package command also builds Javadoc.

Continuous integration with Bamboo

All code is built and tests run automatically on a build server at NCSA whenever changes are committed to directories used by maven. Please confirm that the automated build and tests succeed after committing changes to code or resource files (it may take up to two minutes for a commit-triggered build to start). Functional tests depend on the scripts in src/main/resources and are likely to fail if not updated following changes to these scripts.

Site Url
Build history
Last build
Last successful build

The link to the latest successful build is useful for obtaining the most recently built jar file without building it yourself. Follow the link to the last successful build, click the Artifacts tab, then download the executable jar.

Maintainer deployment:

To deploy a snapshot to the snapshotRepository:

mvn clean deploy

To deploy a new release to maven central, set the version in pom.xml to a non-snapshot version, then deploy with the release profile (which adds package signing and deployment to release staging:

mvn clean deploy -P release

After this, you will need to login to the sonatype oss repository hosting nexus instance, find the staged release in the staging repositories, and perform the release. It should be possible (haven't verified this yet) to perform the release from the command line instead by running:

mvn nexus-staging:release -P release
You can’t perform that action at this time.