benjaminalt / knowrob

KnowRob is a knowledge base for robots. It equips robots with the capability to organize information in re-usable knowledge chunks, and to perform reasoning in an expressive logic formalism. It further provides a set of tools for visualization and acquisition of knowledge.

KnowRob

KnowRob is a knowledge processing system designed for robots. Its purpose is to equip robots with the capability to organize information in re-usable knowledge chunks, and to perform reasoning in an expressive logic. It further provides a set of tools for visualization and acquisition of knowledge.

Getting Started

These instructions will get you a copy of KnowRob up and running on your local machine.

Prerequisites

• ROS (ROS melodic for the master branch)
• SWI Prolog >= 8.2.4 (see Further Information)
• mongo DB server >= 4.4 and libmongoc (see Further Information)
• rosprolog

Installation

KnowRob uses the catkin buildsystem that has been the main ROS buildsystem. We have prepared different .rosinstall setup files that you can add to your ROS workspace as described here.

rosdep update
cd ~/catkin_ws/src
wstool init
wstool merge https://raw.github.com/knowrob/knowrob/master/rosinstall/knowrob-base.rosinstall
wstool update
rosdep install --ignore-src --from-paths .
cd ~/catkin_ws
catkin_make

You may further need to set the SWI_HOME_DIR environment variable to the installation location of swipl:

export SWI_HOME_DIR=/usr/lib/swi-prolog

Launching

In order to interact with other robot components, the Robot Operating System (ROS) is used via rosprolog. rosprolog provides a ROS node that manages a pool of Prolog engines in which KnowRob can be loaded such that its querying interface is exposed via the node. KnowRob provides a launch file that starts the rosprolog node, and initializes KnowRob:

roslaunch knowrob knowrob.launch

Please refer to the rosprolog documentation for how to interact with this node. However, KnowRob can also be launched without ROS node through a script offered by rosprolog:

rosrun rosprolog rosprolog knowrob

Launching KnowRob without the ROS node may help debugging (at the moment the GUI tracing tool of SWI Prolog gtrace does not work via the rosprolog node).

Getting Familiar

Here we provide an overview about functionality of KnowRob.

Querying

The core of KnowRob is an extendible querying interface that provides basic operations ask, tell, forget, and remember. Their argument is some statement written in the KnowRob Querying Language. Language phrases are terms whose semantics is defined in form of Prolog rules using special operators such as ?> (the ask operator), or +> (the tell operator).

One useful CLI for queries is launched with rosrun rosprolog rosprolog_commandline.py

Model

KnowRob structures knowledge according to models represented using RDF. Some models are very basic and domain-independent such as the OWL model that e.g. distinguishes between object and datatype properties, or the toplevel ontology SOMA which is supported by KnowRob. KnowRob Models is a collection of such models that are explicitely supported by KnowRob. However, support for other models may be added through plugins.

Triple Store and Data Access

Knowledge is represented in form of temporalized triples -- each subject-predicate-object triple has an additional field that restricts the temporal scope in which the statement represented by the triple is true. A configurable backend is used to store and retrieve temporalized triples -- as a falback implementation, KnowRob provides a simple MongoDB implementation of a temporalized triple store.

One important aspect in knowledge representation for robots is that a lot of knowledge is implicitly encoded in the control structures of the robot. Hence, one goal is to make the knowledge in robot control structures explicit. KnowRob does that through Ontology-based Data Access (OBDA). So called, semantic data accessors are used to map data to symbols in an ontology, often by accessing some database, or by reading from a message queue, etc.

For more information on database backends in KnowRob, please have a look here.

Reasoning

KnowRob uses an ensemble of reasoners approach where inferences of different reasoners are combined into correlated knowledge pieces. The reason for choosing this approach is that there is no single formalism that is suited for every reasoning tasks. Instead, given a problem, one should decide what the most suitable formalism is to tackle it. Consequently, KnowRob can be configured to solve specific problems by loading corresponding reasoning modules that implement a common interface. KnowRob also ships with a set of reasoning modules including an (incomplete) OWL reasoner, a SWRL reasoner, and some specialized reasoning modules that handle domain-specific problems such as reasoning about time intervals using Allen's interval calculus. More complete information about reasoning in KnowRob can be found here.

Further Information

• Sourcecode documentation is available here
• A blog and more wiki pages are avaiabale at knowrob.org

Installation of SWI-Prolog and MongoDB

• SWI Prolog latest stable version

# If swi-prolog is already installed, check the version
swipl --version
# If it's under 8.2.4, add the ppa of the latest stable version
sudo apt-add-repository -y ppa:swi-prolog/stable
# And update it
sudo apt update
sudo apt upgrade
# or install it, if not present before.
sudo apt install swi-prolog

• MongoDB

# Check the mongodb version
mongod --version
# If below 4.4, an update is needed.
# Updating the mongodb requires either wiping all existing DBs or dumping/restoring them.
# Newer versions are not compatible with old DBs and wouldn't even allow the mongodb service to start
# Therefore, if you want to keep old DBs, store them BEFORE upgading mongodb.
# The following procedure reinstalls mongodb completely with the desired version. 
# All previous deps, settings, DBs of mongodb will be lost!

# Stop the service
sudo systemctl stop mongod.service
# Remove all DBs
sudo rm -r /var/log/mongodb
sudo rm -r /var/lib/mongodb
# Uninstall all mongo packages
# Be aware that this also removes unrelated packages starting with 'mongo*'
sudo apt purge mongo*
# Fetch the latest packages of mongodb-org
wget -qO - https://www.mongodb.org/static/pgp/server-4.4.asc | sudo apt-key add -
echo "deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.4 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-4.4.list
# Update references and install mongodb
sudo apt update
sudo apt install mongodb-org

# Troubleshoot: If dpkg errors occurr, the deps still refer to old versions. Force the new version
# Replace the <version> with your own new version. To this day it is '4.4.10'. 
sudo dpkg -i --force-overwrite /var/cache/apt/archives/mongodb-org-tools_4.4.<version>_amd64.deb

# Try to run the mongodb service
sudo systemctl start mongod.service
# Check if the service is running properly
sudo systemctl status mongod.service
# Refer to the mongodb error code explaination for further insight: 
# https://github.com/mongodb/mongo/blob/master/src/mongo/util/exit_code.h
# Status 62 identifies old DBs in /var/log and /var/lib, so delete them.
# To instead keep them, you'll need to downgrade mongo, dump DBs, upgrade mongo, recreate DBs.
# When it fails to open /var/log/mongodb/mongod.log the permissons for that file are incorrect.
# Either set owner and group of these two paths to mongodb, or reinstall mongodb.