Revisiting the Hardness of Query Answering in Expressive Description Logics

  • Magdalena Ortiz
  • Mantas Šimkus
Part of the Lecture Notes in Computer Science book series (LNCS, volume 8741)


Answering conjunctive queries over Description Logic (DL) knowledge bases is known to be 2ExpTime-hard for the DLs \(\mathcal{ALCI}\), \(\mathcal{SH}\), and their extensions. In this technical note, we revisit these results to identify other equally hard settings. In particular, we show that a simple adaptation of the proof for \(\mathcal{SH}\) proves that query answering is 2ExpTime-hard already for \(\mathcal{ALC}\) if we consider more expressive query languages such as positive existential queries and (restricted classes of) conjunctive regular path queries.


Description Logic Query Language Computation Tree Conjunctive Query Query Answering 
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Copyright information

© Springer International Publishing Switzerland 2014

Authors and Affiliations

  • Magdalena Ortiz
    • 1
  • Mantas Šimkus
    • 1
  1. 1.Institute of Information SystemsVienna University of TechnologyAustria

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