[DL] Next Description Logic Seminar: Anouk Michelle Oudshoorn and Federica Di Stefano

[Quentin Manière]

Dear DL enthusiasts,

we are very happy to announce the next edition of the *Description Logic 
Seminar* on next *Friday 10th of October at 2pm CET* 
(https://dl.kr.org/seminar). This time, we have two speakers: *Anouk 
Michelle Oudshoorn* and *Federica Di Stefano*, both from TU Wien, who 
will talk for 20+5 minutes each. They will respectively tell us about:
*Well-founded SHACL and the Modal Mu-Calculus*
and
*Non-monotonic Description Logics Based on Predicate Minimization*
You can find the respective abstracts below.

The meeting will take place *via Zoom*:
https://uni-leipzig.zoom-x.de/j/68858847568?pwd=eNmvm3hmsu0VdeOba0caeGpRoGiHLy.1

Best wishes,
Elena, Maurice, Bart, and Quentin


/=======/
/Abstracts
=======/

*Well-founded SHACL and the Modal Mu-Calculus*
Different semantics have been considered for recursive SHACL, a language 
designed for expressing constraints on RDF data. As understanding the 
computational features and formal foundations has become essential, we 
focus on the containment problem here. In this talk, we will see that 
under the supported model semantics — any shape assignment goes — 
containment is undecidable. Therefore, we shift our attention to the 
recently introduced well-founded semantics for SHACL and show the tight 
connections between well-founded programs and the modal mu-calculus, and 
some positive results that follow from this reduction. (Based on 
preliminary results with Magdalena Ortiz and Mantas Šimkus)

*Non-monotonic Description Logics Based on Predicate Minimization*
Adding non-monotonic capabilities to Description Logics (DLs) has long 
been one of the greatest aspirations of the DL community. This is 
evidenced by a thriving family of formalisms, among which are 
circumscribed DLs—i.e., DLs equipped with McCarthy's circumscription. At 
the core of circumscription lies predicate minimization. Models of a 
circumscribed knowledge base (KB) are classical models in which the 
extension of some predicates—the so-called minimized predicates—is as 
small as possible. One of the biggest challenges in introducing 
non-monotonic features to DLs is the increase in computational 
complexity, and circumscription is no exception. Despite predicate 
minimization providing a rather natural semantics, reasoning in 
circumscribed DLs is computationally expensive, and undecidability is 
easily encountered—especially when roles are minimized or fixed. For 
this reason, it has become common practice to adopt conditions aimed at 
preserving decidability by appropriately restricting the set of 
minimized and fixed predicates. In this talk, we aim to outline recent 
results on circumscribed DLs and related formalisms, under the 
assumption that roles are minimized or fixed. In addition to pinpointing 
some of the sources of difficulty arising from role minimization, we 
will discuss possible restrictions and alternative semantics—e.g., 
pointwise circumscription—under which decidability can be regained.
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