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<p>Dear members of the DL community,<br>
<br>
<br>
We are happy to announce that the next <b>Description Logic
Online Seminar</b> will take place this <b>Friday, 11th of
April at 2pm CE(S)T</b>. This time, we have two speakers: <b>Lukas
Gerlach</b> from the TU Dresden and <b>Raoul Koudijs</b> from
the University of Amsterdam. <br>
<br>
Join us online on zoom!</p>
<p><br>
<br>
<b>Zoom</b>:
<a class="moz-txt-link-freetext" href="https://uni-leipzig.zoom-x.de/j/69906856451?pwd=j7Kw7SnwwdzUG39346baEElefmBhXS.1">https://uni-leipzig.zoom-x.de/j/69906856451?pwd=j7Kw7SnwwdzUG39346baEElefmBhXS.1</a>
<br>
<br>
<br>
Speaker: <b>Lukas Gerlach</b><br>
<b>Chase Termination - Analytical Hierarchy, Disjunctions,
Sufficient Conditions</b><br>
<br>
I will give an overview of my recent and ongoing works revolving
around chase termination. The chase is a fundamental algorithm for
reasoning with ontologies featuring existential rules. There are
different nuances when asking for termination of this algorithm.
While all of these questions are undecidable, some are more
undecidable than others. We have recently shown that a particular
termination question is complete for the first level of the
analytical hierarchy. I will also give a recap on advances that we
have made in the recent years in pushing generality of some
sufficient conditions for chase termination and non-termination,
particularly for existential rules that also allow disjunctions.<br>
<br>
<br>
Speaker: <b>Raoul Koudijs</b><br>
<b>On the Power and Limitations of Examples for Description Logic
Concepts</b><br>
<br>
Labeled examples are an attractive medium for communicating
complex concepts. Finite characterisations are relevant for
debugging purposes and their existence is a necessary condition
for exact learnability with membership queries. We investigate the
power of labeled examples for describing DL concepts coming from a
specific concept language. Specifically, we systematically study
the existence and efficient computability of finite
characterisations, i.e., finite sets of labeled examples that
uniquely characterise a single concept, for a wide variety of
description logics between EL and ALCQI, both without an ontology
and in the presence of a DL-Lite ontology. We also comment on the
repercussions of our result for exact learning DL concepts with
membership queries only.<br>
<br>
<br>
Further information on the seminar can be found at <b><a class="moz-txt-link-freetext" href="https://dl.kr.org/seminar">https://dl.kr.org/seminar</a></b><br>
<br>
<br>
Best regards,<br>
<br>
Ana Ozaki, Bartosz Bednarczyk, Patrick Koopmann and Quentin
Maniere <br>
</p>
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