Use HermiT in Python

Question

We have an ontology but we need to use the reasoner HermiT to infer the sentiment of a given expression. We have no idea how to use and implement a reasoner in python and we could not find a good explanation on the internet. We found that we can use sync_reasoner() for this, but what does this do exactly? And do we have to call the reasoner manually everytime or does it happen automatically?

Answer 1

You do not need to implement the reasoner. The sync_reasoner() function already calls HermiT internally and does the reasoning for you.

A reasoner will reclassify individuals and classes for you which means it creates a parent-child hierarchy of classes and individuals. When you load an ontology only explicit parent-child relations are represented. However, when you call the reasoner, the parent-child hierarchy is updated to include inferred relations as well.

An example of this is provided in Owlready2-0.5/doc/intro.rst. Before calling sync_reasoner() calling test_pizza.__class__ prints onto.Pizza, which is explicit information. However, after calling sync_reasoner() calling test_pizza.__class__ prints onto.NonVegetarianPizza, which is the inferred information.