[DL] Description Logic Online Seminar, April Edition

[Patrick Koopmann]

Dear members of the DL community,


We are happy to announce that the next *Description Logic Online 
Seminar* will take place this *Friday, 11th of April at 2pm CE(S)T*. 
This time, we have two speakers: *Lukas Gerlach* from the TU Dresden and 
*Raoul Koudijs* from the University of Amsterdam.

Join us online on zoom!



*Zoom*: 
https://uni-leipzig.zoom-x.de/j/69906856451?pwd=j7Kw7SnwwdzUG39346baEElefmBhXS.1 



Speaker: *Lukas Gerlach*
*Chase Termination - Analytical Hierarchy, Disjunctions, Sufficient 
Conditions*

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.


Speaker: *Raoul Koudijs*
*On the Power and Limitations of Examples for Description Logic Concepts*

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.


Further information on the seminar can be found at 
*https://dl.kr.org/seminar*


Best regards,

Ana Ozaki, Bartosz Bednarczyk, Patrick Koopmann and Quentin Maniere
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