A Ground Fact is a Predicate Function with instantiated Predicate Arguments that is assumed to be True.
- By "ground fact", we mean an assertion that uses specified values or literals, without variables.
- http://mb.eschew.org/11 (RDF)
- A ground fact (sometimes called a concrete fact) is a fact that is fully known. All the facts discussed so far in this chapter are ground facts. As an example, consider this statement: "Tom is the owner of Spot." It is easy to identify a subject (Tom), object (Spot), and predicate (owner). Everything is known about the statement, and so the statement is said to be ground. This means it has a solid basis. An equivalent ground fact can be written down right away: <- Tom, owner, Spot -> By comparison, a trickier statement might be: "Tom owns a dog." The subject, object, and predicate can still be identified so the statement is ground. An equivalent fact is <- Tom, owner, dog -> If, in this case, you happen to know that there are many dogs, then the question "Which dog does Tom own?" is left unanswered. In that case, "Tom owns a dog" is not ground because no object (a particular dog) can be identified.