Editing Description logic (section)

=== TBox vs Abox ===
In DL, a distinction is drawn between the so-called [[abox|TBox]] (terminological box) and the [[ABox]] (assertional box). In general, the TBox contains sentences describing concept hierarchies (i.e., relations between [[concept]]s) while the ABox contains [[ground sentence]]s stating where in the hierarchy, individuals belong (i.e., relations between individuals and concepts). For example, the statement:

{{NumBlk|:|Every employee is a person|{{EquationRef|1}}}}

belongs in the TBox, while the statement:

{{NumBlk|:|Bob is an employee|{{EquationRef|2}}}}

belongs in the ABox.

Note that the TBox/ABox distinction is not significant, in the same sense that the two "kinds" of sentences are not treated differently in first-order logic (which subsumes most DL). When translated into first-order logic, a subsumption [[axiom]] like ({{EquationNote|1}}) is simply a conditional restriction to [[unary operation|unary]] [[Predicate (logic)|predicate]]s (concepts) with only variables appearing in it. Clearly, a sentence of this form is not privileged or special over sentences in which only constants ("grounded" values) appear like ({{EquationNote|2}}).