Document

**Published in:** LIPIcs, Volume 220, 25th International Conference on Database Theory (ICDT 2022)

The popular isolation level Multiversion Read Committed (RC) trades some of the strong guarantees of serializability for increased transaction throughput. Sometimes, transaction workloads can be safely executed under RC obtaining serializability at the lower cost of RC. Such workloads are said to be robust against RC. Previous work has yielded a tractable procedure for deciding robustness against RC for workloads generated by transaction programs modeled as transaction templates. An important insight of that work is that, by more accurately modeling transaction programs, we are able to recognize larger sets of workloads as robust. In this work, we increase the modeling power of transaction templates by extending them with functional constraints, which are useful for capturing data dependencies like foreign keys. We show that the incorporation of functional constraints can identify more workloads as robust that otherwise would not be. Even though we establish that the robustness problem becomes undecidable in its most general form, we show that various restrictions on functional constraints lead to decidable and even tractable fragments that can be used to model and test for robustness against RC for realistic scenarios.

Brecht Vandevoort, Bas Ketsman, Christoph Koch, and Frank Neven. Robustness Against Read Committed for Transaction Templates with Functional Constraints. In 25th International Conference on Database Theory (ICDT 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 220, pp. 16:1-16:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{vandevoort_et_al:LIPIcs.ICDT.2022.16, author = {Vandevoort, Brecht and Ketsman, Bas and Koch, Christoph and Neven, Frank}, title = {{Robustness Against Read Committed for Transaction Templates with Functional Constraints}}, booktitle = {25th International Conference on Database Theory (ICDT 2022)}, pages = {16:1--16:17}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-223-5}, ISSN = {1868-8969}, year = {2022}, volume = {220}, editor = {Olteanu, Dan and Vortmeier, Nils}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2022.16}, URN = {urn:nbn:de:0030-drops-158905}, doi = {10.4230/LIPIcs.ICDT.2022.16}, annote = {Keywords: concurrency control, robustness, complexity} }

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**Published in:** LIPIcs, Volume 155, 23rd International Conference on Database Theory (ICDT 2020)

This paper introduces a declarative framework to specify and reason about distributions of data over computing nodes in a distributed setting. More specifically, it proposes distribution constraints which are tuple and equality generating dependencies (tgds and egds) extended with node variables ranging over computing nodes. In particular, they can express co-partitioning constraints and constraints about range-based data distributions by using comparison atoms. The main technical contribution is the study of the implication problem of distribution constraints. While implication is undecidable in general, relevant fragments of so-called data-full constraints are exhibited for which the corresponding implication problems are complete for EXPTIME, PSPACE and NP. These results yield bounds on deciding parallel-correctness for conjunctive queries in the presence of distribution constraints.

Gaetano Geck, Frank Neven, and Thomas Schwentick. Distribution Constraints: The Chase for Distributed Data. In 23rd International Conference on Database Theory (ICDT 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 155, pp. 13:1-13:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{geck_et_al:LIPIcs.ICDT.2020.13, author = {Geck, Gaetano and Neven, Frank and Schwentick, Thomas}, title = {{Distribution Constraints: The Chase for Distributed Data}}, booktitle = {23rd International Conference on Database Theory (ICDT 2020)}, pages = {13:1--13:19}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-139-9}, ISSN = {1868-8969}, year = {2020}, volume = {155}, editor = {Lutz, Carsten and Jung, Jean Christoph}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2020.13}, URN = {urn:nbn:de:0030-drops-119378}, doi = {10.4230/LIPIcs.ICDT.2020.13}, annote = {Keywords: tuple-generating dependencies, chase, conjunctive queries, distributed evaluation} }

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

Recently, Ketsman et al. started the investigation of the parallel evaluation of recursive queries in the Massively Parallel Communication (MPC) model. Among other things, it was shown that parallel-correctness and parallel-boundedness for general Datalog programs is undecidable, by a reduction from the undecidable containment problem for Datalog. Furthermore, economic policies were introduced as a means to specify data distribution in a recursive setting. In this paper, we extend the latter framework to account for more general distributed evaluation strategies in terms of communication policies. We then show that the undecidability of parallel-correctness runs deeper: it already holds for fragments of Datalog, e.g., monadic and frontier-guarded Datalog, with a decidable containment problem, under relatively simple evaluation strategies. These simple evaluation strategies are defined w.r.t. data-moving distribution constraints. We then investigate restrictions of economic policies that yield decidability. In particular, we show that parallel-correctness is 2EXPTIME-complete for monadic and frontier-guarded Datalog under hash-based economic policies. Next, we consider restrictions of data-moving constraints and show that parallel-correctness and parallel-boundedness are 2EXPTIME-complete for frontier-guarded Datalog. Interestingly, distributed evaluation no longer preserves the usual containment relationships between fragments of Datalog. Indeed, not every monadic Datalog program is equivalent to a frontier-guarded one in the distributed setting. We illustrate the latter by considering two alternative settings where in one of these parallel-correctness is decidable for frontier-guarded Datalog but undecidable for monadic Datalog.

Frank Neven, Thomas Schwentick, Christopher Spinrath, and Brecht Vandevoort. Parallel-Correctness and Parallel-Boundedness for Datalog Programs. In 22nd International Conference on Database Theory (ICDT 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 127, pp. 14:1-14:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{neven_et_al:LIPIcs.ICDT.2019.14, author = {Neven, Frank and Schwentick, Thomas and Spinrath, Christopher and Vandevoort, Brecht}, title = {{Parallel-Correctness and Parallel-Boundedness for Datalog Programs}}, booktitle = {22nd International Conference on Database Theory (ICDT 2019)}, pages = {14:1--14:19}, 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.2019.14}, URN = {urn:nbn:de:0030-drops-103165}, doi = {10.4230/LIPIcs.ICDT.2019.14}, annote = {Keywords: Datalog, distributed databases, distributed evaluation, decision problems, complexity} }

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**Published in:** Dagstuhl Manifestos, Volume 7, Issue 1 (2018)

The area of Principles of Data Management (PDM) has made crucial contributions to the development of formal frameworks for understanding and managing
data and knowledge. This work has involved a rich cross-fertilization between
PDM and other disciplines in mathematics and computer science, including logic, complexity theory, and knowledge representation. We anticipate on-going expansion of PDM research as the technology and applications involving data management continue to grow and evolve. In particular, the lifecycle of Big Data Analytics raises a wealth of challenge areas that PDM can help with.
In this report we identify some of the most important research directions where the PDM community has the potential to make significant contributions. This is done from three perspectives: potential practical relevance, results already obtained, and research questions that appear surmountable in the short and medium term.

Serge Abiteboul, Marcelo Arenas, Pablo Barceló, Meghyn Bienvenu, Diego Calvanese, Claire David, Richard Hull, Eyke Hüllermeier, Benny Kimelfeld, Leonid Libkin, Wim Martens, Tova Milo, Filip Murlak, Frank Neven, Magdalena Ortiz, Thomas Schwentick, Julia Stoyanovich, Jianwen Su, Dan Suciu, Victor Vianu, and Ke Yi. Research Directions for Principles of Data Management (Dagstuhl Perspectives Workshop 16151). In Dagstuhl Manifestos, Volume 7, Issue 1, pp. 1-29, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@Article{abiteboul_et_al:DagMan.7.1.1, author = {Abiteboul, Serge and Arenas, Marcelo and Barcel\'{o}, Pablo and Bienvenu, Meghyn and Calvanese, Diego and David, Claire and Hull, Richard and H\"{u}llermeier, Eyke and Kimelfeld, Benny and Libkin, Leonid and Martens, Wim and Milo, Tova and Murlak, Filip and Neven, Frank and Ortiz, Magdalena and Schwentick, Thomas and Stoyanovich, Julia and Su, Jianwen and Suciu, Dan and Vianu, Victor and Yi, Ke}, title = {{Research Directions for Principles of Data Management (Dagstuhl Perspectives Workshop 16151)}}, pages = {1--29}, journal = {Dagstuhl Manifestos}, ISSN = {2193-2433}, year = {2018}, volume = {7}, number = {1}, editor = {Abiteboul, Serge and Arenas, Marcelo and Barcel\'{o}, Pablo and Bienvenu, Meghyn and Calvanese, Diego and David, Claire and Hull, Richard and H\"{u}llermeier, Eyke and Kimelfeld, Benny and Libkin, Leonid and Martens, Wim and Milo, Tova and Murlak, Filip and Neven, Frank and Ortiz, Magdalena and Schwentick, Thomas and Stoyanovich, Julia and Su, Jianwen and Suciu, Dan and Vianu, Victor and Yi, Ke}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/DagMan.7.1.1}, URN = {urn:nbn:de:0030-drops-86772}, doi = {10.4230/DagMan.7.1.1}, annote = {Keywords: database theory, principles of data management, query languages, efficient query processing, query optimization, heterogeneous data, uncertainty, knowledge-enriched data management, machine learning, workflows, human-related data, ethics} }

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**Published in:** LIPIcs, Volume 98, 21st International Conference on Database Theory (ICDT 2018)

SCULPT is a simple schema language inspired by the recent working effort towards a recommendation by the World Wide Web Consortium (W3C) for tabular data and metadata on the Web. In its core, a SCULPT schema consists of a set of rules where left-hand sides select sets of regions in the tabular data and the right-hand sides describe the contents of these regions. A document (divided in cells by row- and column-delimiters) then satisfies a schema if it satisfies every rule. In this paper, we study the satisfiability problem for SCULPT schemas. As SCULPT describes grid-like structures, satisfiability obviously becomes undecidable rather quickly even for very restricted schemas. We define a schema language called L-SCULPT (Lego SCULPT) that restricts the walking power of SCULPT by selecting rectangular shaped areas and only considers tables for which selected regions do not intersect. Depending on the axes used by L-SCULPT, we show that satisfiability is PTIME-complete or undecidable. One of the tractable fragments is practically useful as it extends the structural core of the current W3C proposal for schemas over tabular data. We therefore see how the navigational power of the W3C proposal can be extended while still retaining tractable satisfiability tests.

Johannes Doleschal, Wim Martens, Frank Neven, and Adam Witkowski. Satisfiability for SCULPT-Schemas for CSV-Like Data. In 21st International Conference on Database Theory (ICDT 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 98, pp. 14:1-14:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{doleschal_et_al:LIPIcs.ICDT.2018.14, author = {Doleschal, Johannes and Martens, Wim and Neven, Frank and Witkowski, Adam}, title = {{Satisfiability for SCULPT-Schemas for CSV-Like Data}}, booktitle = {21st International Conference on Database Theory (ICDT 2018)}, pages = {14:1--14:19}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-063-7}, ISSN = {1868-8969}, year = {2018}, volume = {98}, editor = {Kimelfeld, Benny and Amsterdamer, Yael}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2018.14}, URN = {urn:nbn:de:0030-drops-85969}, doi = {10.4230/LIPIcs.ICDT.2018.14}, annote = {Keywords: CSV, schema languages, semi-structured data} }

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**Published in:** LIPIcs, Volume 98, 21st International Conference on Database Theory (ICDT 2018)

Single-round multiway join algorithms first reshuffle data over many servers and then evaluate the query at hand in a parallel and communication-free way. A key question is whether a given distribution policy for the reshuffle is adequate for computing a given query. This property is referred to as parallel-correctness. Another key problem is to detect whether the data reshuffle step can be avoided when evaluating subsequent queries. The latter problem is referred to as transfer of parallel-correctness. This paper extends the study of parallel-correctness and transfer of parallel-correctness of conjunctive queries to incorporate bag semantics. We provide semantical characterizations for both problems, obtain complexity bounds and discuss the relationship with their set semantics counterparts. Finally, we revisit both problems under a modified distribution model that takes advantage of a linear order on compute nodes and obtain tight complexity bounds.

Bas Ketsman, Frank Neven, and Brecht Vandevoort. Parallel-Correctness and Transferability for Conjunctive Queries under Bag Semantics. In 21st International Conference on Database Theory (ICDT 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 98, pp. 18:1-18:16, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{ketsman_et_al:LIPIcs.ICDT.2018.18, author = {Ketsman, Bas and Neven, Frank and Vandevoort, Brecht}, title = {{Parallel-Correctness and Transferability for Conjunctive Queries under Bag Semantics}}, booktitle = {21st International Conference on Database Theory (ICDT 2018)}, pages = {18:1--18:16}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-063-7}, ISSN = {1868-8969}, year = {2018}, volume = {98}, editor = {Kimelfeld, Benny and Amsterdamer, Yael}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2018.18}, URN = {urn:nbn:de:0030-drops-86040}, doi = {10.4230/LIPIcs.ICDT.2018.18}, annote = {Keywords: Conjunctive queries, distributed evaluation, bag semantics} }

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**Published in:** LIPIcs, Volume 48, 19th International Conference on Database Theory (ICDT 2016)

Single-round multiway join algorithms first reshuffle data over many servers and then evaluate the query at hand in a parallel and communication-free way. A key question is whether a given distribution policy for the reshuffle is adequate for computing a given query, also referred to as parallel-correctness. This paper extends the study of the complexity of parallel-correctness and its constituents, parallel-soundness and parallel-completeness, to unions of conjunctive queries with and without negation. As a by-product it is shown that the containment problem for conjunctive queries with negation is coNEXPTIME-complete.

Gaetano Geck, Bas Ketsman, Frank Neven, and Thomas Schwentick. Parallel-Correctness and Containment for Conjunctive Queries with Union and Negation. In 19th International Conference on Database Theory (ICDT 2016). Leibniz International Proceedings in Informatics (LIPIcs), Volume 48, pp. 9:1-9:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2016)

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@InProceedings{geck_et_al:LIPIcs.ICDT.2016.9, author = {Geck, Gaetano and Ketsman, Bas and Neven, Frank and Schwentick, Thomas}, title = {{Parallel-Correctness and Containment for Conjunctive Queries with Union and Negation}}, booktitle = {19th International Conference on Database Theory (ICDT 2016)}, pages = {9:1--9:17}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-95977-002-6}, ISSN = {1868-8969}, year = {2016}, volume = {48}, editor = {Martens, Wim and Zeume, Thomas}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2016.9}, URN = {urn:nbn:de:0030-drops-57787}, doi = {10.4230/LIPIcs.ICDT.2016.9}, annote = {Keywords: Conjunctive queries, distributed evaluation} }

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**Published in:** LIPIcs, Volume 31, 18th International Conference on Database Theory (ICDT 2015)

In a distributed context where data is dispersed over many computing nodes, monotone queries can be evaluated in an eventually consistent and coordination-free manner through a simple but naive broadcasting strategy which makes all data available on every computing node. In this paper, we investigate more economical broadcasting strategies for full conjunctive queries without self-joins that only transmit a part of the local data necessary to evaluate the query at hand. We consider oblivious broadcasting strategies which determine which local facts to broadcast independent of the data at other computing nodes. We introduce the notion of broadcast dependency set (BDS) as a sound and complete formalism to represent locally optimal oblivious broadcasting functions. We provide algorithms to construct a BDS for a given conjunctive query and study the complexity of various decision problems related to these algorithms.

Bas Ketsman and Frank Neven. Optimal Broadcasting Strategies for Conjunctive Queries over Distributed Data. In 18th International Conference on Database Theory (ICDT 2015). Leibniz International Proceedings in Informatics (LIPIcs), Volume 31, pp. 291-307, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2015)

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@InProceedings{ketsman_et_al:LIPIcs.ICDT.2015.291, author = {Ketsman, Bas and Neven, Frank}, title = {{Optimal Broadcasting Strategies for Conjunctive Queries over Distributed Data}}, booktitle = {18th International Conference on Database Theory (ICDT 2015)}, pages = {291--307}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-939897-79-8}, ISSN = {1868-8969}, year = {2015}, volume = {31}, editor = {Arenas, Marcelo and Ugarte, Mart{\'\i}n}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2015.291}, URN = {urn:nbn:de:0030-drops-49913}, doi = {10.4230/LIPIcs.ICDT.2015.291}, annote = {Keywords: Coordination-free evaluation, conjunctive queries, broadcasting} }

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**Published in:** LIPIcs, Volume 31, 18th International Conference on Database Theory (ICDT 2015)

We investigate the class D of queries that distribute over components. These are the queries that can be evaluated by taking the union of the query results over the connected components of the database instance. We show that it is undecidable whether a (positive) Datalog program distributes over components. Additionally, we show that connected Datalog with Negation (the fragment of Datalog with Negation where all rules are connected) provides an effective syntax for Datalog with Negation programs that distribute over components under the stratified as well as under the well-founded semantics. As a corollary, we obtain a simple proof for one of the main results in previous work [Zinn, Green, and Ludäscher, ICDT2012], namely, that the classic win-move query is in F_2 (a particular class of coordination-free queries).

Tom J. Ameloot, Bas Ketsman, Frank Neven, and Daniel Zinn. Datalog Queries Distributing over Components. In 18th International Conference on Database Theory (ICDT 2015). Leibniz International Proceedings in Informatics (LIPIcs), Volume 31, pp. 308-323, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2015)

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@InProceedings{ameloot_et_al:LIPIcs.ICDT.2015.308, author = {Ameloot, Tom J. and Ketsman, Bas and Neven, Frank and Zinn, Daniel}, title = {{Datalog Queries Distributing over Components}}, booktitle = {18th International Conference on Database Theory (ICDT 2015)}, pages = {308--323}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-939897-79-8}, ISSN = {1868-8969}, year = {2015}, volume = {31}, editor = {Arenas, Marcelo and Ugarte, Mart{\'\i}n}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2015.308}, URN = {urn:nbn:de:0030-drops-49920}, doi = {10.4230/LIPIcs.ICDT.2015.308}, annote = {Keywords: Datalog, stratified semantics, well-founded semantics, coordination-free evaluation, distributed databases} }

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**Published in:** LIPIcs, Volume 31, 18th International Conference on Database Theory (ICDT 2015)

We introduce three formal models of distributed systems for query evaluation on massive databases: Distributed Streaming with Register Automata (DSAs), Distributed Streaming with Register Transducers (DSTs), and Distributed Streaming with Register Transducers and Joins (DSTJs). These models are based on the key-value paradigm where the input is transformed into a dataset of key-value pairs, and on each key a local computation is performed on the values associated with that key resulting in another set of key-value pairs. Computation proceeds in a constant number of rounds, where the result of the last round is the input to the next round, and transformation to key-value pairs is required to be generic. The difference between the three models is in the local computation part. In DSAs it is limited to making one pass over its input using a register automaton, while in DSTs it can make two passes: in the first pass it uses a finite-state automaton and in the second it uses a register transducer. The third model DSTJs is an extension of DSTs, where local computations are capable of constructing the Cartesian product of two sets. We obtain the following results: (1) DSAs can evaluate first-order queries over bounded degree databases; (2) DSTs can evaluate semijoin algebra queries over arbitrary databases; (3) DSTJs can evaluate the whole relational algebra over arbitrary databases; (4) DSTJs are strictly stronger than DSTs, which in turn, are strictly stronger than DSAs; (5) within DSAs, DSTs and DSTJs there is a strict hierarchy w.r.t. the number of rounds.

Frank Neven, Nicole Schweikardt, Frédéric Servais, and Tony Tan. Distributed Streaming with Finite Memory. In 18th International Conference on Database Theory (ICDT 2015). Leibniz International Proceedings in Informatics (LIPIcs), Volume 31, pp. 324-341, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2015)

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@InProceedings{neven_et_al:LIPIcs.ICDT.2015.324, author = {Neven, Frank and Schweikardt, Nicole and Servais, Fr\'{e}d\'{e}ric and Tan, Tony}, title = {{Distributed Streaming with Finite Memory}}, booktitle = {18th International Conference on Database Theory (ICDT 2015)}, pages = {324--341}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-939897-79-8}, ISSN = {1868-8969}, year = {2015}, volume = {31}, editor = {Arenas, Marcelo and Ugarte, Mart{\'\i}n}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICDT.2015.324}, URN = {urn:nbn:de:0030-drops-49939}, doi = {10.4230/LIPIcs.ICDT.2015.324}, annote = {Keywords: distributed systems, relational algebra, semijoin algebra, register automata, register transducers.} }

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**Published in:** LIPIcs, Volume 1, 25th International Symposium on Theoretical Aspects of Computer Science (2008)

We study the succinctness of the complement and intersection of
regular expressions. In particular, we show that when constructing
a regular expression defining the complement of a given regular
expression, a double exponential size increase cannot be avoided.
Similarly, when constructing a regular expression defining the
intersection of a fixed and an arbitrary number of regular
expressions, an exponential and double exponential size increase,
respectively, can in worst-case not be avoided. All mentioned
lower bounds improve the existing ones by one exponential and are
tight in the sense that the target expression can be constructed in
the corresponding time class, i.e., exponential or double
exponential time. As a by-product, we generalize a theorem by
Ehrenfeucht and Zeiger stating that there is a class of DFAs which
are exponentially more succinct than regular expressions, to a
fixed four-letter alphabet. When the given regular expressions are
one-unambiguous, as for instance required by the XML Schema
specification, the complement can be computed in polynomial time
whereas the bounds concerning intersection continue to hold. For
the subclass of single-occurrence regular expressions, we prove a
tight exponential lower bound for intersection.

Wouter Gelade and Frank Neven. Succinctness of the Complement and Intersection of Regular Expressions. In 25th International Symposium on Theoretical Aspects of Computer Science. Leibniz International Proceedings in Informatics (LIPIcs), Volume 1, pp. 325-336, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2008)

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@InProceedings{gelade_et_al:LIPIcs.STACS.2008.1354, author = {Gelade, Wouter and Neven, Frank}, title = {{Succinctness of the Complement and Intersection of Regular Expressions}}, booktitle = {25th International Symposium on Theoretical Aspects of Computer Science}, pages = {325--336}, series = {Leibniz International Proceedings in Informatics (LIPIcs)}, ISBN = {978-3-939897-06-4}, ISSN = {1868-8969}, year = {2008}, volume = {1}, editor = {Albers, Susanne and Weil, Pascal}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.STACS.2008.1354}, URN = {urn:nbn:de:0030-drops-13541}, doi = {10.4230/LIPIcs.STACS.2008.1354}, annote = {Keywords: } }

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**Published in:** Dagstuhl Seminar Proceedings, Volume 5061, Foundations of Semistructured Data (2005)

From 06.02.05 to 11.02.05, the Dagstuhl Seminar
05061 ``Foundations of Semistructured Data'' was held
in the International Conference and Research Center (IBFI),
Schloss Dagstuhl.
During the seminar, several participants presented their current
research, and ongoing work and open problems were discussed. Abstracts of
the presentations given during the seminar as well as abstracts of
seminar results and ideas are put together in this paper. The first section
describes the seminar topics and goals in general.
Links to extended abstracts or full papers are provided, if available.

Frank Neven, Thomas Schwentick, and Dan Suciu. 05061 Abstracts Collection – Foundations of Semistructured Data. In Foundations of Semistructured Data. Dagstuhl Seminar Proceedings, Volume 5061, pp. 1-13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2005)

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@InProceedings{neven_et_al:DagSemProc.05061.1, author = {Neven, Frank and Schwentick, Thomas and Suciu, Dan}, title = {{05061 Abstracts Collection – Foundations of Semistructured Data}}, booktitle = {Foundations of Semistructured Data}, pages = {1--13}, series = {Dagstuhl Seminar Proceedings (DagSemProc)}, ISSN = {1862-4405}, year = {2005}, volume = {5061}, editor = {Frank Neven and Thomas Schwentick and Dan Suciu}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.05061.1}, URN = {urn:nbn:de:0030-drops-2330}, doi = {10.4230/DagSemProc.05061.1}, annote = {Keywords: Semistructured data, XML, database theory, document processing} }

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**Published in:** Dagstuhl Seminar Proceedings, Volume 5061, Foundations of Semistructured Data (2005)

As in the first seminar on this topic, the aim o the workshop was to bring together people from the areas related to semi-structured data. However, besides the presentation of recent work, this time the main goal was to identify the main lines of a common framework for future foundational work on semi-structured data. These lines of research are summarized below.
The workshop was of a very interdisciplinary nature with invitees from databases, structured documents, programming languages, information retrieval and formal language theory. Several of the lectures were presented by PhD students. We had four invited speakers and a panel on research evaluation. Due to strong connections between topics treated at this workshop, many of the participants initiated new cooperations and research projects.

Frank Neven, Thomas Schwentick, and Dan Suciu. 05061 Summary – Foundations of Semi-structured Data. In Foundations of Semistructured Data. Dagstuhl Seminar Proceedings, Volume 5061, pp. 1-5, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2005)

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@InProceedings{neven_et_al:DagSemProc.05061.2, author = {Neven, Frank and Schwentick, Thomas and Suciu, Dan}, title = {{05061 Summary – Foundations of Semi-structured Data}}, booktitle = {Foundations of Semistructured Data}, pages = {1--5}, series = {Dagstuhl Seminar Proceedings (DagSemProc)}, ISSN = {1862-4405}, year = {2005}, volume = {5061}, editor = {Frank Neven and Thomas Schwentick and Dan Suciu}, publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik}, address = {Dagstuhl, Germany}, URL = {https://drops.dagstuhl.de/entities/document/10.4230/DagSemProc.05061.2}, URN = {urn:nbn:de:0030-drops-2276}, doi = {10.4230/DagSemProc.05061.2}, annote = {Keywords: Report, summary} }

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