With this article I'm starting the "SciOntology" series in which I'll talk about interesting aspects of ontologies and semantic technologies using examples I hope to be entertaining. I will take for granted that you have installed an ontology editor such as Protégé, or alternatively that you are comfortable with writing ontologies manually and running a reasoner such as Pellet separately. If not, you can take a look at any tutorial you can find online or you can write a comment and I'll be happy to try and help you.