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Use KnowRob from your program

The interactive Prolog shell that rosprolog provides is good for exploring KnowRob, visualizing knowledge, developing new functions and debugging Prolog code. However, if you would like to use KnowRob in your robot's control program, you need a way to send queries from your program. This functionality is provided by the json_prolog package. It provides a service that exposes a Prolog shell via ROS.

You can run the json_prolog service using the following command. It has the same structure as rosprolog, taking a KnowRob package as final argument.

rosrun json_prolog json_prolog ias_semantic_map

Client libraries

The communication with the json_prolog service uses a JSON-encoded format for representing the Prolog terms that form the query. While you can construct these terms manually and call the service directly, it is usally much easier to use one of the provided client libraries. There are libraries for Python, C++, Java and Lisp. Example clients are available in the json_prolog/examples folder; below is the code for sending KnowRob queries from Python via json_prolog.

Python client

#!/usr/bin/env python
import roslib; roslib.load_manifest('json_prolog')
import rospy
import json_prolog
if __name__ == '__main__':
    prolog = json_prolog.Prolog()
    query = prolog.query("member(A, [1, 2, 3, 4]), B = ['x', A]")
    for solution in
        print 'Found solution. A = %s, B = %s' % (solution['A'], solution['B'])

C++ client

#include <string>
#include <iostream>
#include <ros/ros.h>
#include <json_prolog/prolog.h>
using namespace std;
using namespace json_prolog;
int main(int argc, char *argv[])
  ros::init(argc, argv, "test_json_prolog");
  Prolog pl;
  PrologQueryProxy bdgs = pl.query("member(A, [1, 2, 3, 4]), B = ['x', A], C = foo(bar, A, B)");
  for(PrologQueryProxy::iterator it=bdgs.begin();
      it != bdgs.end(); it++)
    PrologBindings bdg = *it;
    cout << "Found solution: " << (bool)(it == bdgs.end()) << endl;
    cout << "A = "<< bdg["A"] << endl;
    cout << "B = " << bdg["B"] << endl;
    cout << "C = " << bdg["C"] << endl;
  return 0;

Java client

import edu.tum.cs.ias.knowrob.json_prolog.Prolog;
import edu.tum.cs.ias.knowrob.json_prolog.PrologBindings;
import edu.tum.cs.ias.knowrob.json_prolog.PrologQueryProxy;
public class JSONPrologTestClient {
	public static void main(String args[]) {
	 Prolog pl = new Prolog();
	 PrologQueryProxy bdgs = pl.query("member(A, [1, 2, 3, 4]), B = ['x', A], C = foo(bar, A, B)");
	 for(PrologBindings bdg : bdgs) {
      System.out.println("Found solution: ");
      System.out.println("A = " + bdg.getBdgs_().get("A") );
      System.out.println("B = " + bdg.getBdgs_().get("B") );
      System.out.println("C = " + bdg.getBdgs_().get("C") );