> The problem with ontological purity is that it would need complicated features that aren't worth bothering with. I think that might be true, but I don't thin

> The problem with ontological purity is that it would need complicated features that aren't worth bothering with. I think that might be true, but I don't think that's usually the problem. I think the problem is that there is almost never one "true" ontology, there are usually multiple overlapping ontologies. And in most cases of real programs, you don't need an ontology anyway. Most programs, if they need to handle ellipses as well as circles, should simply treat everything as an ellipse. If there is a specific time you need to know if something is a circle, write a function to check that. If performance is eaten up checking for circles repeatedly, sort the data into two lists of circular ellipses and non-circular.