This set of lessons (tutorial) is intended to give a broad overview of the content of the Knowledge Base. In an effort to expose you to as much of the knowledge base as possible, we included many examples to illustrate the topics we address. Some of the slides in this tutorial are so simple and self-explanatory that we will give no explanation, others will have many examples of a common type, only some of which will be explained, with the expectation that the reader can fill in the explanation for the rest.
There are many methods for representing knowledge, including written documents, text files, databases, etc. The advantage that Cyc has over these methods is the language in which its knowledge is written, CycL. In CycL, the meanings of statements and inferential connections between statements are encoded in a way that is accessible to a machine. At the present time Natural Languages are virtually meaningless to machines. I can say “all animals have spinal cords. All dogs are animals. My pet is a dog.” From these sentences, a person can infer that my pet has a spinal cord, but a machine cannot, at least not until a machine can understand English sentences.
In the formal language Cyc uses, inference is reduced to a matter of symbol manipulation, and thus something that a machine can do. When an argument is written in CycL, its meaning is encoded in the shape, or symbolic structure, of the assertion it contains. Determining whether or not an argument is valid can be achieved by checking for certain simple physical patterns in the CycL sentence representing its premises and conclusions.
The Knowledge Base (KB) itself comprises a massive taxonomy of concepts and specifically-defined relationships that describe how those concepts are related.
This figure represents the context of the knowledge arranged by degrees of generality, with a small layer of abstract generalizations at the top and a large layer of real-world facts at the bottom.
The Upper Ontology doesn’t say much about the world at all. It represents very general relations between very general concepts. For example, it contains the assertions to the effect that every event is a temporal thing, every temporal thing is an individual, and every individual is a thing. “Thing” is Cyc’s most general concept. Everything whatsoever is an instance of “thing.”
The KB contains several core theories that represent general facts about space, time, and causality. These are the theories that are essential to almost all common-sense reasoning.
Domain-Specific Theories are more specific than core theories. These theories apply to special areas of interest like military movement, the propagation of diseases, finance, chemistry, etc. These are the theories that make Cyc particularly useful, but are not necessary for common sense reasoning.
The final layer contains what is sometimes called “ground-level facts.” These are statements about particular individuals in the world. For example, “John has anthrax” is a specific statement about one person. Generalizations would not go here, they would go in a layer above. Anything you can imagine as a headline in a newspaper would probably go here.
This concludes the introduction to the tutorial that surveys the contents of the Knowledge Base.