Permanent knowledge base

[alex-mitrevski]

Problem description

The ROSPlan knowledge base, which we are interfacing with, is kept in memory, which means that knowledge is lost when the planning system is not running. In some scenarios, however, we should be able to preserve the available knowledge even if a robot is temporarily shut down (for example in the lab manager scenario introduced by b-it-bots/mas_domestic_robotics#233, where the robot should preserve the occupancy of lab sitting spots during the day).

Suggested solution

Adapt the knowledge base interface in ROPOD's task planner, which saves knowledge items to a MongoDB database instead of keeping them in memory.

Caveats

If the knowledge base is permanently kept, we will need a strategy for verifying the correctness of the stored knowledge, otherwise the robot might be acting on outdated information.