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This software is in development (TRL 6).

Knowledge Engine

DOI

Knowledge Engine logo

Welcome to the source code repository of the Knowledge Engine. This README should help you understand what the Knowledge Engine is, and how to use it.

In short, the Knowledge Engine is an interoperability solution that wants to make it easier for different knowledge bases to communicate.

Knowledge base is a term to describe "the system that connects with the interoperability platform". It can be anything. Examples include, databases, sensors, or even GUIs.

Communication is made easier by using concepts from an ontology: a common domain-specific model that the knowledge bases will have to agree upon.

For example, if one knowledge base is interested in some kind of data (e.g., names of dogs: ?dog a ex:Dog . ?dog ex:hasName ?dogName .), and several other knowledge bases provide such data, the data is automatically gathered and merged when such a query is executed.

The Knowledge Engine consists of a number of components:

  • A smart connector is used by knowledge bases to exchange data with other knowledge bases. The smart connector gives the knowledge base a way to (1) register the kind of knowledge they want to exchange and in which way, and (2) do the actual knowledge exchange.
  • A Knowledge Engine runtime is a runtime in which one or more smart connectors can exist. These can exchange data with eachother, and, if configured correctly, also with smart connectors in other Knowledge Engine runtimes.
  • (optional) A knowledge directory is used as a simple discovery mechanism for several Knowledge Engine runtimes to become aware of eachother's existence.

To quickly see how to use the Knowledge Engine through examples, see ./examples/.

The rest of this README is structured as follows:

Demonstration videos and tutorials

This video gives a high-level introduction to the Knowledge Engine, with a simple demonstration of how we aimed to use it in the InterConnect project.

Following the previous video, this video shows the realisation, and explains more about a pilot in the Netherlands that uses the Knowledge Engine to control energy flexibility in a 22-story building with 160 appartments.

This video tutorial gives technical details about how to develop knowledge bases and connect them with the Knowledge Engine.

Starting a Knowledge Engine runtime

Starting a Knowledge Engine runtime can be done in several ways, with Docker, with Java, and in a more minimal way with Java.

Remote runtimes* REST API Java API
Docker ✅ ✅ ❌
Java ✅ ✅ ✅
Java (minimal) ✅ ❌ ✅

* Requires additional configuration

Running with Docker

The easiest way to start a Knowledge Engine runtime is with Docker:

docker run \
	-p 8280:8280 \
	ghcr.io/tno/knowledge-engine/smart-connector:1.2.5

The Knowledge Engine runtime is now available to use via the REST API at base URL http://localhost:8280/rest on your host machine. For usage instructions, see the section on using the REST API.

However, running it in the above way does not support data exchange with remote runtimes; it can only be used to exchange data with other smart connectors in the same runtime.

To interact with other runtimes, it needs additional configuration:

  • An additional port mapping for the socket that listens for communication from other runtimes.
  • KE_RUNTIME_EXPOSED_URL: The URL via which the above socket is available for communication from the other runtime(s). You need to make sure the traffic is correctly routed to the container's port 8081 with a reverse proxy.
  • KD_URL: The URL on which to find the knowledge directory (to discover peers).

The configuration can be set as follows:

docker run \
  -p 8280:8280 \
  -p 8081:8081 \
  -e KD_URL=https://knowledge-directory.example.org \
  -e KE_RUNTIME_EXPOSED_URL=https://your-domain.example.org:8081 \
  ghcr.io/tno/knowledge-engine/smart-connector:1.2.5

Running with Java

If you prefer not to use Docker, you can also use the JAR to run it directly in your JVM:

# Where the knowledge directory is located
export KD_URL=https://knowledge-directory.example.org
# Port where the runtime will listen for connections from other
# smart connectors.
export KE_RUNTIME_PORT=8081
# URL where the runtime will be available from other runtimes.
export KE_RUNTIME_EXPOSED_URL=https://your-domain.example.org:8081

# Start it. The argument (8280) denotes the port number at which it
# will listen for connections to the Knowledge Engine REST API.
java -jar -Dorg.slf4j.simpleLogger.logFile=smart-connector.log \
  smart-connector-rest-dist-1.2.5-with-dependencies.jar 8280

The JAR can be retrieved by compiling the project:

mvn clean package -DskipTests
# the relevant JAR will be in `./smart-connector-rest-dist/target/`

Advanced administration

For further advanced instructions on administering a Knowledge Engine runtime, refer to the advanced section of this document.

Running with Java without the REST API

In constrained environments, it may be preferable to use the Java API directly, and not use the REST API.

For this, you need to be in a Java project, import our packages, implement the KnowledgeBase interface, and start a smart connector with a SmartConnectorBuilder. An example of this can be found in the ./examples/ folder.

Integrating with the Knowledge Engine

Again, there are several options here: use the REST API, the Java API or the Knowledge Mapper*.

Available in JVM Available whenever HTTP is possible Easy configuration for selected data sources
REST API ✅ ✅ ❌
Java API ✅ ❌ ❌
Knowledge Mapper* ❌ ❌ ✅

* Under development, and currently not available as open-source software.

Using the REST API

Assuming there is a REST API instance running at a known host, you can use these instructions to help you get started with making a client for it.

To make the client, it needs to talk HTTP, and conform to our API specification. With the API specification, you will be able to:

  • Register your knowledge base via the /sc path.
  • Register knowledge interactions for your knowledge base via the /sc/ki path.
  • Trigger new proactive knowledge requests via the /sc/ask and /sc/post paths.
  • Long-poll (GET) and respond to (POST) knowledge requests from the network via the /sc/handle path.

In the examples/rest-api folder, there is an example Docker Compose project with 3 knowledge bases that publish, store, and present sensor data through a single Knowledge Engine runtime. This example covers all four knowledge interaction types, but does not cover all features the REST API provides.

Using the Java API

In the Java API Example module, the Java API is used to share bindings through a POST knowledge interaction as they appear on an MQTT queue. Another knowledge base receives those bindings through a REACT knowledge interaction an prints them to the console.

Performance benchmark

A preliminary performence benchmark of the Knowledge Engine is available in this repository.

Based on this benchmark, the minimum requirements for the Knowledge Engine are:

  • i3-3040 Intel processor at 3.4 GHz
  • 8 Gbit RAM
  • 250Gb SSD drives

Of course, it highly depends on how you want to use the Knowledge Engine, because the reasoner, for example, increases these requirements.

Developer information

This section gives more detailed information about the project's structure, and is targeted towards developers who contribute code to the project.

Components

The Knowledge Engine project consists of the following Maven modules:

  • smart-connector
    • This is the implementation of the smart connector, with the Java developer API. For instructions on how to use it, refer to the documentation.
  • smart-connector-api
    • This module contains interfaces for the smart connector and other classes. It is made as a separate module so that it is easy to use different implementations of the interfaces.
  • smart-connector-rest-server
    • This module contains the REST API layer that is built on top of the Java Developer API.
  • smart-connector-rest-dist
    • A distribution of the server that provides the REST API layer for your smart connector(s), and uses the smart connector implementation from the smart-connector module. For instructions on how to use it, refer to the section below. For instructions on how to set it up, refer to this section.
  • admin-ui
    • A REST API which provides meta-data about smart connectors in a knowledge network. Can be used in an administration inferface for a knowledge network. It is implemented as a knowledge base that uses metadata of other knowledge bases.

Release steps

These are instructions on what to do when we release a new version of the knowledge engine.

  1. Update all relevant version references and make sure they are correct and non-SNAPSHOT:
    • this README.md file
    • all pom.xml files
    • openapi-sc.yaml version
    • Docker image tags in the Docker Compose examples.
  2. Make a commit for the release, and tag it with git tag {x}.{y}.{z}.
  3. mvn deploy (for this you need Deploy-Token or Private-Token configured in your Maven's settings.xml, see GitLab's documentation on this)
  4. Push the commit and the tag.
  5. Build and push the new Docker images to GitLab:
docker buildx build ./smart-connector-rest-dist --platform linux/arm64,linux/amd64 --tag docker-registry.inesctec.pt/interconnect/knowledge-engine/smart-connector-rest-dist:1.2.5 --push
docker buildx build ./knowledge-directory --platform linux/arm64,linux/amd64 --tag docker-registry.inesctec.pt/interconnect/knowledge-engine/knowledge-directory:1.2.5 --push
docker buildx build ./admin-ui --platform linux/arm64,linux/amd64 --tag docker-registry.inesctec.pt/interconnect/knowledge-engine/admin-ui:1.2.5 --push
  1. Build and push the new Docker images to GitHub:
docker buildx build ./smart-connector-rest-dist --platform linux/arm64,linux/amd64 --tag ghcr.io/tno/knowledge-engine/smart-connector:1.2.5 --push
docker buildx build ./knowledge-directory --platform linux/arm64,linux/amd64 --tag ghcr.io/tno/knowledge-engine/knowledge-directory:1.2.5 --push
docker buildx build ./admin-ui --platform linux/arm64,linux/amd64 --tag ghcr.io/tno/knowledge-engine/admin-ui:1.2.5 --push
  1. Prepare the next SNAPSHOT version and make a commit for that too.
    1. openapi-sc.yaml
    2. pom.xml
    3. Leave the non-SNAPSHOT version in this README, and in the Docker Compose examples.
  2. In GitLab, create a new release at https://gitlab.inesctec.pt/interconnect/knowledge-engine/-/releases
    1. Use the new tag for the release
    2. Write release notes
    3. Find the latest version of the package at https://gitlab.inesctec.pt/interconnect/knowledge-engine/-/packages/976 and copy the link to the JAR with dependencies. Include it in "Release assets" with type "Package" and link title "Knowledge Engine REST server JAR (with dependencies)" (see previous releases)
  3. In GitHub, create a new release at https://github.com/TNO/knowledge-engine/releases/new
    1. Use the new tag for the release
    2. Include the same release notes
  4. Inform mailing list(s) (and the blog) about the new release.

(advanced) Administering a Knowledge Engine runtime

To start a new instance of the REST API knowledge engine version 1.2.5, make sure you have git checkout 1.2.5 the tag 1.2.5. Now make sure you run the mvn clean install command successfully from the root of the repository.

Starting the Knowledge Engine in local mode

When no additional configuration parameters are provided, the Knowledge Engine will by default run in local mode. This means you can create multiple smart connectors that can communicate with each other through the REST API, but the Knowledge Engine will not connect to a knowledge directory and will not be able to connect with smart connectors running in other runtimes.

Now, go to the target directory of the smart-connector-rest-dist module:

cd smart-connector-rest-dist/target

Finally, start the server (note that you can configure a log file by including the -Dorg.slf4j.simpleLogger.logFile=ke.log system property to the JVM):

java -Dorg.slf4j.simpleLogger.logFile=ke.log -cp "smart-connector-rest-dist-1.2.5.jar:dependency/*" eu.knowledge.engine.rest.Main 8280

If you want to run in it in the background, you can use the nohup linux command (which does not use the simpleLogger configuration system property, but redirects the standard err/out):

nohup java -cp "smart-connector-rest-dist-1.2.5.jar:dependency/*" eu.knowledge.engine.rest.Main 8280 > ke.log

Starting the Knowledge Engine in distributed mode

The Knowledge Engine can also start in distributed mode, where it connects with a remote knowledge directory and where different instances of the Knowledge Engine (each instance hosting one or more smart connectors) can communicate with each other. More information about starting the Knowledge Engine in distributed mode can be found in the documentation.

Additional configuration environment variables

Increasing the wait time for other KBs to respond

By default, a Smart Connector waits 10 seconds max for a reply from another Smart Connector when sending an ASK/POST message. This time is configurable via the KE_KB_WAIT_TIMEOUT environment variable and setting it to 0 means the Smart Connector will wait indefinitely (this can be useful when dealing with Human KBs).

Increasing the HTTP timeouts

By default, a KER waits 5 seconds max for a HTTP response from another KER when sending a message via the inter-KER protocol. The time is configurable via the KE_HTTP_TIMEOUT environment variable.