Editing Description logic (section)

===First-order logic===
Many DLs are [[Decidability (logic)|decidable]] [[fragment (logic)|fragments]] of [[first-order logic]] (FOL)<ref name="DLHB"/> and are usually fragments of [[two-variable logic]] or [[guarded logic]]. In addition, some DLs have features that are not covered in FOL; this includes ''concrete domains'' (such as integer or strings, which can be used as ranges for roles such as ''hasAge'' or ''hasName'') or an operator on roles for the [[transitive closure]] of that role.<ref name="DLHB"/>