Saturday, October 2, 2010


One part of our project will be to build an ontology for our robot. An ontology is a model of the world, condensed into the relevant parts for a given problem. For example, our robot will have motors, digital and analog sensors, and so on. These would be represented in the ontology, but possibly more, like a simple model of the robot's surrounding: Hills, obstacles and so on.

At school, we're using a really easy-to use Ontology editor called Protégé; it also has some nice visualization features. The result might be an "owl" file; a standard xml file for ontologies that can easily be accessed from a program.

I'm just starting to learn this topic and not quite sure what the advantage of an ontology as opposed to e.g. an object graph is. Both model reality in some way, both are hierarchical and have properties, reference objects and so on.

One of the differences is that an ontology also models the objects, the individual instances. For example, you might model a city's subway network. In a class hierarchy, you could only model things like Subway, Station and whatever is needed for the model. Creating the objects will either mean hardcoding them or writing some code that reads the objects from a file; the former is inflexible and the second is error-prone and redundant. An ontology can (and will) contain the explicit lines and stations of the city along with the definitions, and neither of the above is needed.

The second diference is its position in context with reasoning. Reasoning is the main reason for the existence of ontologies, and therefore there are a few (hopefully good) APIs out there that make it easy to write statements like "how many stations are there on subway line 1?" or "should I go left or right around the obstacle to reach my target faster?"

And this is where we get to rule-based programming. Pulling conclusions out of the ontology is half of the work of writing a rule. See you next time!

1 comment:

nantuko84 said...

I worked with ontologies in a project (I used Protégé either, and it was version 3.4.4 (against 4.x) as it allowed to use sparql). For reasoning you may be interested in the reasoner we used: