Knowledge and reasoning#

PAL’s robots includes a knowledge base called KnowledgeCore. Thanks to the knowledge base, you can store, query and reason on facts about the robot activities and environment.

KnowledgeCore stores triples (like RDF/OWL triples), and provides an API accessible via a simple Python wrapper or a ROSAPI.

KnowledgeCore can also perform symbolic reasoning: it integrates with the reasonable OWL2 RL reasoner to provide OWL2 semantics and fast knowledge materialisation.

Simple example#

This example uses our simple Python wrapper to interact with the knowledge base:

from knowledge_core.api import KB

rospy.init_node("test_knowledge_base")

kb = KB()

def on_robot_entering_clara_property(evt):
  print("A robot entered Clara's %s: %s" (evt[0]["place"], evt[0]["robot"]))

kb += "ari rdf:type Robot"
kb += ["clara looksAt ari", "ari isIn kitchen"]

kb.subscribe(["?robot isIn ?place", "?place belongsTo clara", "?robot rdf:type Robot"], on_robot_entering_clara_property)

# ...nothing happens yet, as we have not told the robot that the 'kitchen'
# belonged to 'clara'...

kb += "kitchen belongsTo clara"

# the event is now triggered!


# try as well:
# kb -= "clara looksAt ari" to remove facts
# kb["* rdf:type Robot"] to query the knowledge base

rospy.spin()

will print:

A robot entered Clara's kitchen: ari

Special features#

In addition to storing and querying facts, KnowledgeCore has several advanced features.

Multi-models#

KnowledgeCore is intended for dynamic environments, with possibly several contexts/agents requiring separate knowledge models.

New models can be created at any time and each operation (like knowledge addition/retractation/query) can operate on a specific subset of models.

Each models are also independently classified by the reasoner.

See KnowledgeCore models for details.

Event system#

KnowledgeCore provides a mechanism to subscribe to some conditions (like: an instance of a given type is added to the knowledge base, some statement becomes true, etc.) and get notified back.

Reasoning#

KnowledgeCore provides RDFS/OWL reasoning capabilities via the reasonable reasoner.

See reasonable README for the exact level of support of the different OWL2 RL rules.