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Documents authored by Pieris, Andreas


Document
Absolute Expressiveness of Subgraph-Based Centrality Measures

Authors: Andreas Pieris and Jorge Salas

Published in: LIPIcs, Volume 255, 26th International Conference on Database Theory (ICDT 2023)


Abstract
In graph-based applications, a common task is to pinpoint the most important or "central" vertex in a (directed or undirected) graph, or rank the vertices of a graph according to their importance. To this end, a plethora of so-called centrality measures have been proposed in the literature. Such measures assess which vertices in a graph are the most important ones by analyzing the structure of the underlying graph. A family of centrality measures that are suited for graph databases has been recently proposed by relying on the following simple principle: the importance of a vertex in a graph is relative to the number of "relevant" connected subgraphs surrounding it; we refer to the members of this family as subgraph-based centrality measures. Although it has been shown that such measures enjoy several favourable properties, their absolute expressiveness remains largely unexplored. The goal of this work is to precisely characterize the absolute expressiveness of the family of subgraph-based centrality measures by considering both directed and undirected graphs. To this end, we characterize when an arbitrary centrality measure is a subgraph-based one, or a subgraph-based measure relative to the induced ranking. These characterizations provide us with technical tools that allow us to determine whether well-established centrality measures are subgraph-based. Such a classification, apart from being interesting in its own right, gives useful insights on the structural similarities and differences among existing centrality measures.

Cite as

Andreas Pieris and Jorge Salas. Absolute Expressiveness of Subgraph-Based Centrality Measures. In 26th International Conference on Database Theory (ICDT 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 255, pp. 9:1-9:18, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2023)


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@InProceedings{pieris_et_al:LIPIcs.ICDT.2023.9,
  author =	{Pieris, Andreas and Salas, Jorge},
  title =	{{Absolute Expressiveness of Subgraph-Based Centrality Measures}},
  booktitle =	{26th International Conference on Database Theory (ICDT 2023)},
  pages =	{9:1--9:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-270-9},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{255},
  editor =	{Geerts, Floris and Vandevoort, Brecht},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2023.9},
  URN =		{urn:nbn:de:0030-drops-177516},
  doi =		{10.4230/LIPIcs.ICDT.2023.9},
  annote =	{Keywords: Graph centrality measures, ranking, expressiveness}
}
Document
Oblivious Chase Termination: The Sticky Case

Authors: Marco Calautti and Andreas Pieris

Published in: LIPIcs, Volume 127, 22nd International Conference on Database Theory (ICDT 2019)


Abstract
The chase procedure is one of the most fundamental algorithmic tools in database theory. A key algorithmic task is uniform chase termination, i.e., given a set of tuple-generating dependencies (tgds), is it the case that the chase under this set of tgds terminates, for every input database? In view of the fact that this problem is undecidable, no matter which version of the chase we consider, it is natural to ask whether well-behaved classes of tgds, introduced in different contexts such as ontological reasoning, make our problem decidable. In this work, we consider a prominent decidability paradigm for tgds, called stickiness. We show that for sticky sets of tgds, uniform chase termination is decidable if we focus on the (semi-)oblivious chase, and we pinpoint its exact complexity: PSpace-complete in general, and NLogSpace-complete for predicates of bounded arity. These complexity results are obtained via graph-based syntactic characterizations of chase termination that are of independent interest.

Cite as

Marco Calautti and Andreas Pieris. Oblivious Chase Termination: The Sticky Case. In 22nd International Conference on Database Theory (ICDT 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 127, pp. 17:1-17:18, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2019)


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@InProceedings{calautti_et_al:LIPIcs.ICDT.2019.17,
  author =	{Calautti, Marco and Pieris, Andreas},
  title =	{{Oblivious Chase Termination: The Sticky Case}},
  booktitle =	{22nd International Conference on Database Theory (ICDT 2019)},
  pages =	{17:1--17:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-101-6},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{127},
  editor =	{Barcelo, Pablo and Calautti, Marco},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2019.17},
  URN =		{urn:nbn:de:0030-drops-103197},
  doi =		{10.4230/LIPIcs.ICDT.2019.17},
  annote =	{Keywords: Chase procedure, tuple-generating dependencies, stickiness, termination, computational complexity}
}
Document
Additive First-Order Queries

Authors: Gerald Berger, Martin Otto, Andreas Pieris, Dimitri Surinx, and Jan Van den Bussche

Published in: LIPIcs, Volume 127, 22nd International Conference on Database Theory (ICDT 2019)


Abstract
A database query q is called additive if q(A U B) = q(A) U q(B) for domain-disjoint input databases A and B. Additivity allows the computation of the query result to be parallelised over the connected components of the input database. We define the "connected formulas" as a syntactic fragment of first-order logic, and show that a first-order query is additive if and only if it expressible by a connected formula. This characterisation specializes to the guarded fragment of first-order logic. We also show that additivity is decidable for formulas of the guarded fragment, establish the computational complexity, and do the same for positive-existential formulas. Our results hold when restricting attention to finite structures, as is common in database theory, but also hold in the unrestricted setting.

Cite as

Gerald Berger, Martin Otto, Andreas Pieris, Dimitri Surinx, and Jan Van den Bussche. Additive First-Order Queries. In 22nd International Conference on Database Theory (ICDT 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 127, pp. 19:1-19:14, Schloss Dagstuhl - Leibniz-Zentrum für Informatik (2019)


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@InProceedings{berger_et_al:LIPIcs.ICDT.2019.19,
  author =	{Berger, Gerald and Otto, Martin and Pieris, Andreas and Surinx, Dimitri and Van den Bussche, Jan},
  title =	{{Additive First-Order Queries}},
  booktitle =	{22nd International Conference on Database Theory (ICDT 2019)},
  pages =	{19:1--19:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-101-6},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{127},
  editor =	{Barcelo, Pablo and Calautti, Marco},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2019.19},
  URN =		{urn:nbn:de:0030-drops-103217},
  doi =		{10.4230/LIPIcs.ICDT.2019.19},
  annote =	{Keywords: Expressive power}
}
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