Published online by Cambridge University Press: 15 October 2021
The inexpressive Description Logic (DL) ${\cal F}{{\cal L}_0}$, which has conjunction and value restriction as its only concept constructors, had fallen into disrepute when it turned out that reasoning in
${\cal F}{{\cal L}_0}$ w.r.t. general TBoxes is ExpTime-complete, that is, as hard as in the considerably more expressive logic
${\cal A}{\cal L}{\cal C}$. In this paper, we rehabilitate
${\cal F}{{\cal L}_0}$ by presenting a dedicated subsumption algorithm for
${\cal F}{{\cal L}_0}$, which is much simpler than the tableau-based algorithms employed by highly optimized DL reasoners. Our experiments show that the performance of our novel algorithm, as prototypically implemented in our
${\cal F}{{\cal L}_0}$wer reasoner, compares very well with that of the highly optimized reasoners.
${\cal F}{{\cal L}_0}$wer can also deal with ontologies written in the extension
${\cal F}{{\cal L}_ \bot }$ of
${\cal F}{{\cal L}_0}$ with the top and the bottom concept by employing a polynomial-time reduction, shown in this paper, which eliminates top and bottom. We also investigate the complexity of reasoning in DLs related to the Horn-fragments of
${\cal F}{{\cal L}_0}$ and
${\cal F}{{\cal L}_ \bot }$.
This paper is under consideration in Theory and Practice of Logic Programming (TPLP).