Computers & Society/Semantic Web/Ontology

According to a fundamental principle that "Everything is mediated through language" we can infer the derived and more precise principle that "Everything computable is mediated through programming language". Let us canonize these two principles as axioms:

  • Axiom 1: Everything is mediated through language.
  • Axiom 2: Everything computable is mediated through programming language.

We may regard them as self-evident truths. But if you are worried about such canonization then you ought to delve further and seek evidence and proof. In other words, do not believe in them unless you feel very sure that they are worth taking as foundation for further work. How might we find such evidence?

Ontology is considered to be about "that which exists". Do not be surprised to find that many people have very different views on what that means exactly. For example, one often reads about the Unicorn (a kind of one-horned animal). Some people say that it is non-existent. It is just a figment of the imagination. Other people say that it exists, precisely because we have the language to talk about it. In this book we will take the latter view that if we can talk about it in a precise way then for all practical purposes the Unicorn is with us. One might imagine a future where we might be able to bring the Unicorn into actual physical existence. But that is futuristic.

One thing we can be more or less certain about is that in the Western Tradition of Philosophy, the Father of Ontology was Aristotle.

OWL—the Semantic Web Ontology LanguageEdit

There are three variants of OWL:

  • OWL-Lite
  • OWL-DL, where the DL stands for description logic
  • OWL-Full

We recommend OWL-DL in this course.


The most important thing to do is to get started as soon as possible in describing our world in terms of OWL-DL. What world is that you might say? Well, it is the world of Computers & Society.

How will we describe the Unicorn? Is it not (like) a horse with one horn? We introduce two concepts: horse and horn. Using these we might describe the unicorn as

  • Unicorn isa Horse
  • Unicorn hasThing Horn


  • For practical work on Semantic Web Ontology (OWL) we recommend the Protégé Editor from Stanford.