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Outline

overview-architecture.png

In this tutorial you will:

  • Learn how to create a model composed of two parts, how to split it into two parts again and persist them with Spring Data CDO.
  • Subscribe to a ROS2 topic in Java, and write an incoming data stream into bigraph node attributes.
  • Define a conditional bigraph reaction rule that evaluates attributes and rewrites only the relevant part of the model.

The running example on the following pages models an agent (i.e., a drone) with an energy level that is updated based on a streamed integer value from ROS2 (e.g., /echo with std_msgs/Int16). When the value is "low enough," a rule turns the agent’s energy marker from HIGH to LOW.

The complete example project can be found here: bigraphs-by-examples.streaming-bigraphs

Software Stack:

Prerequisites​

ROS2​

ROS2 (Humble) and rosbridge websocket server running, for example:

# ROS 2 + rosbridge (example for Humble)
$ sudo apt install ros-humble-rosbridge-suite
$ source /opt/ros/humble/setup.bash
$ ros2 launch rosbridge_server rosbridge_websocket_launch.xml

Test publisher:

$ ros2 topic pub /echo std_msgs/Int16 "{data: 123}"

Eclipse CDO​

This is where the bigraphical models are stored.

The actual implementation provides an in-memory CDO repository, so you can experiment without setting up a full database. See the class CDOStandaloneServerTest for details.

To start the in-memory CDO database (non-persistent storage):

$ mvn test -DrunDisabledTests=true -Dtest="CDOStandaloneServerTest#run_server_test_01"

You can also run this method directly from your IDE, such as Eclipse, IntelliJ IDEA, or VSCode.