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<p>Dear DL enthusiasts,<br>
<br>
we are very happy to announce the next edition of the <b>Description
Logic Seminar</b> on next <b>Friday 10th of October at 2pm CET</b>
(<a class="moz-txt-link-freetext" href="https://dl.kr.org/seminar">https://dl.kr.org/seminar</a>).
This time, we have two speakers: <b>Anouk Michelle Oudshoorn</b>
and <b>Federica Di Stefano</b>, both from TU Wien, who will talk
for 20+5 minutes each. They will respectively tell us about:<br>
<b>Well-founded SHACL and the Modal Mu-Calculus</b><br>
and <br>
<b>Non-monotonic Description Logics Based on Predicate
Minimization</b><br>
You can find the respective abstracts below. <br>
<br>
The meeting will take place <b>via Zoom</b>:<br>
<a class="moz-txt-link-freetext"
href="https://uni-leipzig.zoom-x.de/j/68858847568?pwd=eNmvm3hmsu0VdeOba0caeGpRoGiHLy.1">https://uni-leipzig.zoom-x.de/j/68858847568?pwd=eNmvm3hmsu0VdeOba0caeGpRoGiHLy.1</a><br>
<br>
Best wishes,<br>
Elena, Maurice, Bart, and Quentin <br>
</p>
<p><br>
<i>=======</i><br>
<i>Abstracts<br>
=======</i><br>
<br>
<b>Well-founded SHACL and the Modal Mu-Calculus</b><br>
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)</p>
<p><b>Non-monotonic Description Logics Based on Predicate
Minimization</b><br>
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.</p>
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