The following lectures and exercises are based on the material I have developed for the course on Open Information Systems at the Vrije Universteit Brussel. I was the lecturer from 2013-2014 to 2015-2016 (three years), and in 2019-2020. Some of the material presented here haas also been repurposed and refined for public seminars.
All work is licensed under a CC BY-NC-SA 4.0 International License, unless where explicitely mentioned otherwise.
The first in a series of lectures on knowledge representation on the Web. We introduce the notion of "ontology" and its role in so-called "open information systems". We conclude by introducing ontologies for the Semantic Web.
In this lecture, we will cover both RDF and RDF(S). The first is a data model, and the latter a simple ontology language built on top of that model. Graduate students are assumed to be familiar with XML and XML Schema, but that assumption is not necessary for the lectures presented here.
Remember, RDF is a data model. Ontologies require ontology languages (such as the Web Ontology Language described later on) for which adequate tools exist. For RDF, however, most adequate tooling for "merely" performs syntactic checks rather than semantic checks.
Two fairly "fancy" editors with support for RDF (via plugins) are Visual Studio Code and Atom. The former might be more lightweight, easier to install, and proposes the installation of plugins upon or saving files of a particular type.
TURTLE syntax highlighting in Visual Studio Code
RDF(S) is too weak if we want to adequately capture our Universe of Discourse in an ontology. The Web Ontology Language (OWL) provides a language that allows us to do just that. Description Logics (DL) provided the foundations of OWL. To understand OWL in the next lecture, we need to understand DLs. In this lecture, I introduce important concepts of DLs: vocabulary, grammar, and semantics; the Open World and Unique Name Assumptions; and reasoning tasks with the Tableau Algorithm.