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Documents authored by Bhaskar, Ashwin

Document
DOI: 10.4230/LIPIcs.FSTTCS.2025.14
Regulating Synchronous Data Exchange to Meet Control Flow and Data Specifications

Authors: Ashwin Bhaskar and M. Praveen

Published in: LIPIcs, Volume 360, 45th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2025)

Abstract
When multiple software components interact via method calls, we may want to ensure that the order of invoked methods and the arguments provided adhere to some specification. The classic problem associated with interface automata checks for the existence of a mediator whose intention is to act as a buffer in between method invocations so that invocations do not go unanswered. We extend the base model underlying interface automata, enabling them to exchange integer values - one automaton generates an integer value and outputs it by firing a generating transition and another automaton receives the value by synchronously firing a receiving transition. Transitions in the automata can have guards with linear order constraints on the exchanged values, influencing which methods can or can not be invoked later. So the generated values influence the sequences of invocations that are enabled. We specify desirable properties of the sequence of method calls and the arguments passed to them using an extension of Linear Temporal Logic (LTL). We consider the interoperability problem, which is to check if it is possible to generate integer values in such a way that all enabled sequences satisfy the given specification. We show that the interoperability problem is undecidable in general, even when there are only two participating automata. We show decidability in the case where guards on generating transitions can only have equality constraints on the exchanged value (but receiving transitions can continue to have linear order constraints). We model this problem as a game between two players, one trying to generate integer values such that violating sequences are disabled while the other player tries to dig out violating sequences that are enabled. Interoperability is equivalent to the first player having a winning strategy. We solve this game via a finite abstraction, which results in a symbolic game. We then show that winning strategies for the symbolic game can be translated to winning strategies for the original game over integers.
Cite as

Ashwin Bhaskar and M. Praveen. Regulating Synchronous Data Exchange to Meet Control Flow and Data Specifications. In 45th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 360, pp. 14:1-14:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{bhaskar_et_al:LIPIcs.FSTTCS.2025.14,
  author =	{Bhaskar, Ashwin and Praveen, M.},
  title =	{{Regulating Synchronous Data Exchange to Meet Control Flow and Data Specifications}},
  booktitle =	{45th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2025)},
  pages =	{14:1--14:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-406-2},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{360},
  editor =	{Aiswarya, C. and Mehta, Ruta and Roy, Subhajit},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2025.14},
  URN =		{urn:nbn:de:0030-drops-250962},
  doi =		{10.4230/LIPIcs.FSTTCS.2025.14},
  annote =	{Keywords: Distributed Systems, Interface Automata, Registers, Parity Games}
}
Document
DOI: 10.4230/LIPIcs.FSTTCS.2023.41
Constraint LTL with Remote Access

Authors: Ashwin Bhaskar and M. Praveen

Published in: LIPIcs, Volume 284, 43rd IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2023)

Abstract
Constraint Linear Temporal Logic (CLTL) is an extension of LTL that is interpreted on sequences of valuations of variables over an infinite domain. The atomic formulas are interpreted as constraints on the valuations. The atomic formulas can constrain valuations at the current position and positions that are a fixed distance apart (e.g., the previous position or the second previous position and so on). The satisfiability problem for CLTL is known to be Pspace-complete. We generalize CLTL to let atomic formulas access positions that are unboundedly far away in the past. We annotate the sequence of valuations with letters from a finite alphabet and use regular expressions on the finite alphabet to control how atomic formulas access past positions. We prove that the satisfiability problem for this extension of the logic is decidable in cases where the domain is dense and open with respect to a linear order (e.g., rational numbers with the usual linear order). We prove that it is also decidable over integers with linear order and equality.
Cite as

Ashwin Bhaskar and M. Praveen. Constraint LTL with Remote Access. In 43rd IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 284, pp. 41:1-41:21, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{bhaskar_et_al:LIPIcs.FSTTCS.2023.41,
  author =	{Bhaskar, Ashwin and Praveen, M.},
  title =	{{Constraint LTL with Remote Access}},
  booktitle =	{43rd IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2023)},
  pages =	{41:1--41:21},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-304-1},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{284},
  editor =	{Bouyer, Patricia and Srinivasan, Srikanth},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2023.41},
  URN =		{urn:nbn:de:0030-drops-194142},
  doi =		{10.4230/LIPIcs.FSTTCS.2023.41},
  annote =	{Keywords: Constraint LTL, Regular Expressions, MSO formulas, Satisfiability, B\"{u}chi automata}
}
Document
DOI: 10.4230/LIPIcs.TIME.2022.8
Realizability Problem for Constraint LTL

Authors: Ashwin Bhaskar and M. Praveen

Published in: LIPIcs, Volume 247, 29th International Symposium on Temporal Representation and Reasoning (TIME 2022)

Abstract
Constraint linear-time temporal logic (CLTL) is an extension of LTL that is interpreted on sequences of valuations of variables over an infinite domain. The atomic formulas are interpreted as constraints on the valuations. The atomic formulas can constrain valuations over a range of positions along a sequence, with the range being bounded by a parameter depending on the formula. The satisfiability and model checking problems for CLTL have been studied by Demri and D’Souza. We consider the realizability problem for CLTL. The set of variables is partitioned into two parts, with each part controlled by a player. Players take turns to choose valuations for their variables, generating a sequence of valuations. The winning condition is specified by a CLTL formula - the first player wins if the sequence of valuations satisfies the specified formula. We study the decidability of checking whether the first player has a winning strategy in the realizability game for a given CLTL formula. We prove that it is decidable in the case where the domain satisfies the completion property, a property introduced by Balbiani and Condotta in the context of satisfiability. We prove that it is undecidable over (ℤ, < , =), the domain of integers with order and equality. We prove that over (ℤ, < , =), it is decidable if the atomic constraints in the formula can only constrain the current valuations of variables belonging to the second player, but there are no such restrictions for the variables belonging to the first player. We call this single-sided games.
Cite as

Ashwin Bhaskar and M. Praveen. Realizability Problem for Constraint LTL. In 29th International Symposium on Temporal Representation and Reasoning (TIME 2022). Leibniz International Proceedings in Informatics (LIPIcs), Volume 247, pp. 8:1-8:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2022)

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@InProceedings{bhaskar_et_al:LIPIcs.TIME.2022.8,
  author =	{Bhaskar, Ashwin and Praveen, M.},
  title =	{{Realizability Problem for Constraint LTL}},
  booktitle =	{29th International Symposium on Temporal Representation and Reasoning (TIME 2022)},
  pages =	{8:1--8:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-262-4},
  ISSN =	{1868-8969},
  year =	{2022},
  volume =	{247},
  editor =	{Artikis, Alexander and Posenato, Roberto and Tonetta, Stefano},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TIME.2022.8},
  URN =		{urn:nbn:de:0030-drops-172556},
  doi =		{10.4230/LIPIcs.TIME.2022.8},
  annote =	{Keywords: Realizability, constraint LTL, Strategy trees, Tree automata}
}
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