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DOI: 10.4230/LIPIcs.CONCUR.2024.5

MITL Model Checking via Generalized Timed Automata and a New Liveness Algorithm

Authors: S. Akshay, Paul Gastin, R. Govind, and B. Srivathsan

Published in: LIPIcs, Volume 311, 35th International Conference on Concurrency Theory (CONCUR 2024)

Abstract

The translation of Metric Interval Temporal Logic (MITL) to timed automata is a topic that has been extensively studied. A key challenge here is the conversion of future modalities into equivalent automata. Typical conversions equip the automata with a guess-and-check mechanism to ascertain the truth of future modalities. Guess-and-check can be naturally implemented via alternation. However, since timed automata tools do not handle alternation, existing methods perform an additional step of converting the alternating timed automata into timed automata. This "de-alternation" step proceeds by an intricate finite abstraction of the space of configurations of the alternating automaton. Recently, a model of generalized timed automata (GTA) has been proposed. The model comes with several powerful additional features, and yet, the best known zone-based reachability algorithms for timed automata have been extended to the GTA model, with the same complexity for all the zone operations. An attractive feature of GTAs is the presence of future clocks which act like timers that guess a time to an event and stay alive until a timeout. Future clocks seem to provide another natural way to implement the guess-and-check: start the future clock with a guessed time to an event and check its occurrence using a timeout. Indeed, using this feature, we provide a new concise translation from MITL to GTA. In particular, for the timed until modality, our translation offers an exponential improvement w.r.t. the state-of-the-art. Thanks to this conversion, MITL model checking reduces to checking liveness for GTAs. However, no liveness algorithm is known for GTAs. Due to the presence of future clocks, there is no finite time-abstract bisimulation (region equivalence) for GTAs, whereas liveness algorithms for timed automata crucially rely on the presence of the finite region equivalence. As our second contribution, we provide a new zone-based algorithm for checking Büchi non-emptiness in GTAs, which circumvents this fundamental challenge.

Cite as

S. Akshay, Paul Gastin, R. Govind, and B. Srivathsan. MITL Model Checking via Generalized Timed Automata and a New Liveness Algorithm. In 35th International Conference on Concurrency Theory (CONCUR 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 311, pp. 5:1-5:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{akshay_et_al:LIPIcs.CONCUR.2024.5,
  author =	{Akshay, S. and Gastin, Paul and Govind, R. and Srivathsan, B.},
  title =	{{MITL Model Checking via Generalized Timed Automata and a New Liveness Algorithm}},
  booktitle =	{35th International Conference on Concurrency Theory (CONCUR 2024)},
  pages =	{5:1--5:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-339-3},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{311},
  editor =	{Majumdar, Rupak and Silva, Alexandra},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.CONCUR.2024.5},
  URN =		{urn:nbn:de:0030-drops-207774},
  doi =		{10.4230/LIPIcs.CONCUR.2024.5},
  annote =	{Keywords: MITL model checking, timed automata, zones, liveness}
}

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DOI: 10.4230/LIPIcs.MFCS.2024.13

A Direct Translation from LTL with Past to Deterministic Rabin Automata

Authors: Shaun Azzopardi, David Lidell, and Nir Piterman

Published in: LIPIcs, Volume 306, 49th International Symposium on Mathematical Foundations of Computer Science (MFCS 2024)

Abstract

We present a translation from linear temporal logic with past to deterministic Rabin automata. The translation is direct in the sense that it does not rely on intermediate non-deterministic automata, and asymptotically optimal, resulting in Rabin automata of doubly exponential size. It is based on two main notions. One is that it is possible to encode the history contained in the prefix of a word, as relevant for the formula under consideration, by performing simple rewrites of the formula itself. As a consequence, a formula involving past operators can (through such rewrites, which involve alternating between weak and strong versions of past operators in the formula’s syntax tree) be correctly evaluated at an arbitrary point in the future without requiring backtracking through the word. The other is that this allows us to generalize to linear temporal logic with past the result that the language of a pure-future formula can be decomposed into a Boolean combination of simpler languages, for which deterministic automata with simple acceptance conditions are easily constructed.

Cite as

Shaun Azzopardi, David Lidell, and Nir Piterman. A Direct Translation from LTL with Past to Deterministic Rabin Automata. In 49th International Symposium on Mathematical Foundations of Computer Science (MFCS 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 306, pp. 13:1-13:15, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{azzopardi_et_al:LIPIcs.MFCS.2024.13,
  author =	{Azzopardi, Shaun and Lidell, David and Piterman, Nir},
  title =	{{A Direct Translation from LTL with Past to Deterministic Rabin Automata}},
  booktitle =	{49th International Symposium on Mathematical Foundations of Computer Science (MFCS 2024)},
  pages =	{13:1--13:15},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-335-5},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{306},
  editor =	{Kr\'{a}lovi\v{c}, Rastislav and Ku\v{c}era, Anton{\'\i}n},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2024.13},
  URN =		{urn:nbn:de:0030-drops-205694},
  doi =		{10.4230/LIPIcs.MFCS.2024.13},
  annote =	{Keywords: Linear temporal logic, \omega-automata, determinization}
}

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Track B: Automata, Logic, Semantics, and Theory of Programming

DOI: 10.4230/LIPIcs.ICALP.2024.150

Homogeneity and Homogenizability: Hard Problems for the Logic SNP

Authors: Jakub Rydval

Published in: LIPIcs, Volume 297, 51st International Colloquium on Automata, Languages, and Programming (ICALP 2024)

Abstract

The infinite-domain CSP dichotomy conjecture extends the finite-domain CSP dichotomy theorem to reducts of finitely bounded homogeneous structures. Every countable finitely bounded homogeneous structure is uniquely described by a universal first-order sentence up to isomorphism, and every reduct of such a structure by a sentence of the logic SNP. By Fraïssé’s Theorem, testing the existence of a finitely bounded homogeneous structure for a given universal first-order sentence is equivalent to testing the amalgamation property for the class of its finite models. The present paper motivates a complexity-theoretic view on the classification problem for finitely bounded homogeneous structures. We show that this meta-problem is EXPSPACE-hard or PSPACE-hard, depending on whether the input is specified by a universal sentence or a set of forbidden substructures. By relaxing the input to SNP sentences and the question to the existence of a structure with a finitely bounded homogeneous expansion, we obtain a different meta-problem, closely related to the question of homogenizability. We show that this second meta-problem is already undecidable, even if the input SNP sentence comes from the Datalog fragment and uses at most binary relation symbols. As a byproduct of our proof, we also get the undecidability of some other properties for Datalog programs, e.g., whether they can be rewritten in the logic MMSNP, whether they solve some finite-domain CSP, or whether they define a structure with a homogeneous Ramsey expansion in a finite relational signature.

Cite as

Jakub Rydval. Homogeneity and Homogenizability: Hard Problems for the Logic SNP. In 51st International Colloquium on Automata, Languages, and Programming (ICALP 2024). Leibniz International Proceedings in Informatics (LIPIcs), Volume 297, pp. 150:1-150:20, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2024)

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@InProceedings{rydval:LIPIcs.ICALP.2024.150,
  author =	{Rydval, Jakub},
  title =	{{Homogeneity and Homogenizability: Hard Problems for the Logic SNP}},
  booktitle =	{51st International Colloquium on Automata, Languages, and Programming (ICALP 2024)},
  pages =	{150:1--150:20},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-322-5},
  ISSN =	{1868-8969},
  year =	{2024},
  volume =	{297},
  editor =	{Bringmann, Karl and Grohe, Martin and Puppis, Gabriele and Svensson, Ola},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2024.150},
  URN =		{urn:nbn:de:0030-drops-202939},
  doi =		{10.4230/LIPIcs.ICALP.2024.150},
  annote =	{Keywords: constraint satisfaction problems, finitely bounded, homogeneous, amalgamation property, universal, SNP, homogenizable}
}

Document

DOI: 10.4230/LIPIcs.TIME.2023.2

LTL over Finite Words Can Be Exponentially More Succinct Than Pure-Past LTL, and vice versa

Authors: Alessandro Artale, Luca Geatti, Nicola Gigante, Andrea Mazzullo, and Angelo Montanari

Published in: LIPIcs, Volume 278, 30th International Symposium on Temporal Representation and Reasoning (TIME 2023)

Abstract

Linear Temporal Logic over finite traces (LTL_𝖿) has proved itself to be an important and effective formalism in formal verification as well as in artificial intelligence. Pure past LTL_𝖿 (pLTL) is the logic obtained from LTL_𝖿 by replacing each (future) temporal operator by a corresponding past one, and is naturally interpreted at the end of a finite trace. It is known that each property definable in LTL_𝖿 is also definable in pLTL, and ǐceversa. However, despite being extensively used in practice, to the best of our knowledge, there is no systematic study of their succinctness. In this paper, we investigate the succinctness of LTL_𝖿 and pLTL. First, we prove that pLTL can be exponentially more succinct than LTL_𝖿 by showing that there exists a property definable with a pLTL formula of size n such that the size of all LTL_𝖿 formulas defining it is at least exponential in n. Then, we prove that LTL_𝖿 can be exponentially more succinct than pLTL as well. This result shows that, although being expressively equivalent, LTL_𝖿 and pLTL are incomparable when succinctness is concerned. In addition, we study the succinctness of Safety-LTL (the syntactic safety fragment of LTL over infinite traces) with respect to its canonical form G(pLTL), whose formulas are of the form G(α), G being the globally operator and α a pLTL formula. We prove that G(pLTL) can be exponentially more succinct than Safety-LTL, and that the same holds for the dual cosafety fragment.

Cite as

Alessandro Artale, Luca Geatti, Nicola Gigante, Andrea Mazzullo, and Angelo Montanari. LTL over Finite Words Can Be Exponentially More Succinct Than Pure-Past LTL, and vice versa. In 30th International Symposium on Temporal Representation and Reasoning (TIME 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 278, pp. 2:1-2:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{artale_et_al:LIPIcs.TIME.2023.2,
  author =	{Artale, Alessandro and Geatti, Luca and Gigante, Nicola and Mazzullo, Andrea and Montanari, Angelo},
  title =	{{LTL over Finite Words Can Be Exponentially More Succinct Than Pure-Past LTL, and vice versa}},
  booktitle =	{30th International Symposium on Temporal Representation and Reasoning (TIME 2023)},
  pages =	{2:1--2:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-298-3},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{278},
  editor =	{Artikis, Alexander and Bruse, Florian and Hunsberger, Luke},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TIME.2023.2},
  URN =		{urn:nbn:de:0030-drops-190927},
  doi =		{10.4230/LIPIcs.TIME.2023.2},
  annote =	{Keywords: Temporal Logic, Succinctness, LTLf, Finite Traces, Pure past LTL}
}

Document

Extended Abstract

DOI: 10.4230/LIPIcs.TIME.2023.22

Qualitative past Timeline-Based Games (Extended Abstract)

Authors: Renato Acampora, Luca Geatti, Nicola Gigante, and Angelo Montanari

Published in: LIPIcs, Volume 278, 30th International Symposium on Temporal Representation and Reasoning (TIME 2023)

Abstract

This extended abstract discusses timeline-based planning, a modeling approach that offers a unique way to model complex systems. Recently, the timeline-based planning framework has been extended to handle general nondeterminism in a game-theoretic setting, resulting in timeline-based games. In this context, the problem of establishing whether a timeline-based game admits a winning strategy and synthesizing such a strategy have been addressed. We propose exploring simpler yet expressive fragments of timeline-based games by leveraging results about the role of past operators in synthesis from temporal logic specifications. The qualitative fragment of timeline-based planning is a good starting point for this exploration. We suggest introducing syntactic restrictions on synchronization rules so that they only constrain the behavior of the system before the current time point, which is expected to lower the complexity of synthesizing timeline-based games to EXPTIME.

Cite as

Renato Acampora, Luca Geatti, Nicola Gigante, and Angelo Montanari. Qualitative past Timeline-Based Games (Extended Abstract). In 30th International Symposium on Temporal Representation and Reasoning (TIME 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 278, pp. 22:1-22:3, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{acampora_et_al:LIPIcs.TIME.2023.22,
  author =	{Acampora, Renato and Geatti, Luca and Gigante, Nicola and Montanari, Angelo},
  title =	{{Qualitative past Timeline-Based Games}},
  booktitle =	{30th International Symposium on Temporal Representation and Reasoning (TIME 2023)},
  pages =	{22:1--22:3},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-298-3},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{278},
  editor =	{Artikis, Alexander and Bruse, Florian and Hunsberger, Luke},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TIME.2023.22},
  URN =		{urn:nbn:de:0030-drops-191125},
  doi =		{10.4230/LIPIcs.TIME.2023.22},
  annote =	{Keywords: Automata, Planning, Temporal Reasoning}
}

Document

DOI: 10.4230/LIPIcs.TIME.2021.8

Past Matters: Supporting LTL+Past in the BLACK Satisfiability Checker

Authors: Luca Geatti, Nicola Gigante, Angelo Montanari, and Gabriele Venturato

Published in: LIPIcs, Volume 206, 28th International Symposium on Temporal Representation and Reasoning (TIME 2021)

Abstract

LTL+Past is the extension of Linear Temporal Logic (LTL) supporting past temporal operators. The addition of the past does not add expressive power, but does increase the usability of the language both in formal verification and in artificial intelligence, e.g., in the context of multi-agent systems. In this paper, we add the support of past operators to BLACK, a satisfiability checker for LTL based on a SAT encoding of a tree-shaped tableau system. We implement two ways of supporting the past in the tool. The first one is an equisatisfiable translation that removes the past operators, obtaining a future-only formula that can be solved with the original LTL engine. The second one extends the SAT encoding of the underlying tableau to directly support the tableau rules that deal with past operators. We describe both approaches and experimentally compare the two between themselves and with the νXmv model checker, obtaining promising results.

Cite as

Luca Geatti, Nicola Gigante, Angelo Montanari, and Gabriele Venturato. Past Matters: Supporting LTL+Past in the BLACK Satisfiability Checker. In 28th International Symposium on Temporal Representation and Reasoning (TIME 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 206, pp. 8:1-8:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{geatti_et_al:LIPIcs.TIME.2021.8,
  author =	{Geatti, Luca and Gigante, Nicola and Montanari, Angelo and Venturato, Gabriele},
  title =	{{Past Matters: Supporting LTL+Past in the BLACK Satisfiability Checker}},
  booktitle =	{28th International Symposium on Temporal Representation and Reasoning (TIME 2021)},
  pages =	{8:1--8:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-206-8},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{206},
  editor =	{Combi, Carlo and Eder, Johann and Reynolds, Mark},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TIME.2021.8},
  URN =		{urn:nbn:de:0030-drops-147846},
  doi =		{10.4230/LIPIcs.TIME.2021.8},
  annote =	{Keywords: SAT, LTL, LTL+Past, Tableaux}
}

Document

DOI: 10.4230/LIPIcs.TIME.2021.9

Pspace-Completeness of the Temporal Logic of Sub-Intervals and Suffixes

Authors: Laura Bozzelli, Angelo Montanari, Adriano Peron, and Pietro Sala

Published in: LIPIcs, Volume 206, 28th International Symposium on Temporal Representation and Reasoning (TIME 2021)

Abstract

In this paper, we establish Pspace-completeness of the finite satisfiability and model checking problems for the fragment of Halpern and Shoham interval logic with modality ⟨E⟩, for the "suffix" relation on pairs of intervals, and modality ⟨D⟩, for the "sub-interval" relation, under the homogeneity assumption. The result significantly improves the Expspace upper bound recently established for the same fragment, and proves the rather surprising fact that the complexity of the considered problems does not change when we add either the modality for suffixes (⟨E⟩) or, symmetrically, the modality for prefixes (⟨B⟩) to the logic of sub-intervals (featuring only ⟨D⟩).

Cite as

Laura Bozzelli, Angelo Montanari, Adriano Peron, and Pietro Sala. Pspace-Completeness of the Temporal Logic of Sub-Intervals and Suffixes. In 28th International Symposium on Temporal Representation and Reasoning (TIME 2021). Leibniz International Proceedings in Informatics (LIPIcs), Volume 206, pp. 9:1-9:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2021)

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@InProceedings{bozzelli_et_al:LIPIcs.TIME.2021.9,
  author =	{Bozzelli, Laura and Montanari, Angelo and Peron, Adriano and Sala, Pietro},
  title =	{{Pspace-Completeness of the Temporal Logic of Sub-Intervals and Suffixes}},
  booktitle =	{28th International Symposium on Temporal Representation and Reasoning (TIME 2021)},
  pages =	{9:1--9:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-206-8},
  ISSN =	{1868-8969},
  year =	{2021},
  volume =	{206},
  editor =	{Combi, Carlo and Eder, Johann and Reynolds, Mark},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TIME.2021.9},
  URN =		{urn:nbn:de:0030-drops-147853},
  doi =		{10.4230/LIPIcs.TIME.2021.9},
  annote =	{Keywords: Interval temporal logic, Satisfiability, Model checking}
}

Document

DOI: 10.4230/LIPIcs.TIME.2020.16

Complexity of Qualitative Timeline-Based Planning

Authors: Dario Della Monica, Nicola Gigante, Salvatore La Torre, and Angelo Montanari

Published in: LIPIcs, Volume 178, 27th International Symposium on Temporal Representation and Reasoning (TIME 2020)

Abstract

The timeline-based approach to automated planning was originally developed in the context of space missions. In this approach, problem domains are expressed as systems consisting of independent but interacting components whose behaviors over time, the timelines, are governed by a set of temporal constraints, called synchronization rules. Although timeline-based system descriptions have been successfully used in practice for decades, the research on the theoretical aspects only started recently. In the last few years, some interesting results have been shown concerning both its expressive power and the computational complexity of the related planning problem. In particular, the general problem has been proved to be EXPSPACE-complete. Given the applicability of the approach in many practical scenarios, it is thus natural to ask whether computationally simpler but still expressive fragments can be identified. In this paper, we study the timeline-based planning problem with the restriction that only qualitative synchronization rules, i.e., rules without explicit time bounds in the constraints, are allowed. We show that the problem becomes PSPACE-complete.

Cite as

Dario Della Monica, Nicola Gigante, Salvatore La Torre, and Angelo Montanari. Complexity of Qualitative Timeline-Based Planning. In 27th International Symposium on Temporal Representation and Reasoning (TIME 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 178, pp. 16:1-16:13, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{dellamonica_et_al:LIPIcs.TIME.2020.16,
  author =	{Della Monica, Dario and Gigante, Nicola and La Torre, Salvatore and Montanari, Angelo},
  title =	{{Complexity of Qualitative Timeline-Based Planning}},
  booktitle =	{27th International Symposium on Temporal Representation and Reasoning (TIME 2020)},
  pages =	{16:1--16:13},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-167-2},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{178},
  editor =	{Mu\~{n}oz-Velasco, Emilio and Ozaki, Ana and Theobald, Martin},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TIME.2020.16},
  URN =		{urn:nbn:de:0030-drops-129847},
  doi =		{10.4230/LIPIcs.TIME.2020.16},
  annote =	{Keywords: Timeline-based planning, qualitative temporal constraints, complexity}
}

Document

DOI: 10.4230/LIPIcs.TIME.2020.17

A Note on C² Interpreted over Finite Data-Words

Authors: Bartosz Bednarczyk and Piotr Witkowski

Published in: LIPIcs, Volume 178, 27th International Symposium on Temporal Representation and Reasoning (TIME 2020)

Abstract

We consider the satisfiability problem for the two-variable fragment of first-order logic extended with counting quantifiers, interpreted over finite words with data, denoted here with C²[≤ , succ, ∼, π_bin]. In our scenario, we allow for using arbitrary many uninterpreted binary predicates from π_bin, two navigational predicates ≤ and succ over word positions as well as a data-equality predicate ∼. We prove that the obtained logic is undecidable, which contrasts with the decidability of the logic without counting by Montanari, Pazzaglia and Sala [Angelo Montanari et al., 2016]. We supplement our results with decidability for several sub-fragments of C²[≤ , succ, ∼, π_bin], e.g. without binary predicates, without successor succ, or under the assumption that the total number of positions carrying the same data value in a data-word is bounded by an a priori given constant.

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Bartosz Bednarczyk and Piotr Witkowski. A Note on C² Interpreted over Finite Data-Words. In 27th International Symposium on Temporal Representation and Reasoning (TIME 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 178, pp. 17:1-17:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{bednarczyk_et_al:LIPIcs.TIME.2020.17,
  author =	{Bednarczyk, Bartosz and Witkowski, Piotr},
  title =	{{A Note on C² Interpreted over Finite Data-Words}},
  booktitle =	{27th International Symposium on Temporal Representation and Reasoning (TIME 2020)},
  pages =	{17:1--17:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-167-2},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{178},
  editor =	{Mu\~{n}oz-Velasco, Emilio and Ozaki, Ana and Theobald, Martin},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TIME.2020.17},
  URN =		{urn:nbn:de:0030-drops-129850},
  doi =		{10.4230/LIPIcs.TIME.2020.17},
  annote =	{Keywords: Two-variable logic, data-words, VASS, decidability, undecidability, counting}
}

Document

DOI: 10.4230/LIPIcs.MFCS.2020.21

On a Temporal Logic of Prefixes and Infixes

Authors: Laura Bozzelli, Angelo Montanari, Adriano Peron, and Pietro Sala

Published in: LIPIcs, Volume 170, 45th International Symposium on Mathematical Foundations of Computer Science (MFCS 2020)

Abstract

A classic result by Stockmeyer [Stockmeyer, 1974] gives a non-elementary lower bound to the emptiness problem for star-free generalized regular expressions. This result is intimately connected to the satisfiability problem for interval temporal logic, notably for formulas that make use of the so-called chop operator. Such an operator can indeed be interpreted as the inverse of the concatenation operation on regular languages, and this correspondence enables reductions between non-emptiness of star-free generalized regular expressions and satisfiability of formulas of the interval temporal logic of the chop operator under the homogeneity assumption [Halpern et al., 1983]. In this paper, we study the complexity of the satisfiability problem for a suitable weakening of the chop interval temporal logic, that can be equivalently viewed as a fragment of Halpern and Shoham interval logic featuring the operators B, for "begins", corresponding to the prefix relation on pairs of intervals, and D, for "during", corresponding to the infix relation. The homogeneous models of the considered logic naturally correspond to languages defined by restricted forms of regular expressions, that use union, complementation, and the inverses of the prefix and infix relations.

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Laura Bozzelli, Angelo Montanari, Adriano Peron, and Pietro Sala. On a Temporal Logic of Prefixes and Infixes. In 45th International Symposium on Mathematical Foundations of Computer Science (MFCS 2020). Leibniz International Proceedings in Informatics (LIPIcs), Volume 170, pp. 21:1-21:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2020)

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@InProceedings{bozzelli_et_al:LIPIcs.MFCS.2020.21,
  author =	{Bozzelli, Laura and Montanari, Angelo and Peron, Adriano and Sala, Pietro},
  title =	{{On a Temporal Logic of Prefixes and Infixes}},
  booktitle =	{45th International Symposium on Mathematical Foundations of Computer Science (MFCS 2020)},
  pages =	{21:1--21:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-159-7},
  ISSN =	{1868-8969},
  year =	{2020},
  volume =	{170},
  editor =	{Esparza, Javier and Kr\'{a}l', Daniel},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.MFCS.2020.21},
  URN =		{urn:nbn:de:0030-drops-126898},
  doi =		{10.4230/LIPIcs.MFCS.2020.21},
  annote =	{Keywords: Interval Temporal Logic, Star-Free Regular Languages, Satisfiability, Complexity}
}

Document

DOI: 10.4230/LIPIcs.FSTTCS.2019.33

Interval Temporal Logic for Visibly Pushdown Systems

Authors: Laura Bozzelli, Angelo Montanari, and Adriano Peron

Published in: LIPIcs, Volume 150, 39th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2019)

Abstract

In this paper, we introduce and investigate an extension of Halpern and Shoham’s interval temporal logic HS for the specification and verification of branching-time context-free requirements of pushdown systems under a state-based semantics over Kripke structures. Both homogeneity and visibility are assumed. The proposed logic, called nested BHS, supports branching-time both in the past and in the future, and is able to express non-regular properties of linear and branching behaviours of procedural contexts in a natural way. It strictly subsumes well-known linear time context-free extensions of LTL such as CaRet [R. Alur et al., 2004] and NWTL [R. Alur et al., 2007]. The main result is the decidability of the visibly pushdown model-checking problem against nested BHS. The proof exploits a non-trivial automata-theoretic construction.

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Laura Bozzelli, Angelo Montanari, and Adriano Peron. Interval Temporal Logic for Visibly Pushdown Systems. In 39th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 150, pp. 33:1-33:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{bozzelli_et_al:LIPIcs.FSTTCS.2019.33,
  author =	{Bozzelli, Laura and Montanari, Angelo and Peron, Adriano},
  title =	{{Interval Temporal Logic for Visibly Pushdown Systems}},
  booktitle =	{39th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2019)},
  pages =	{33:1--33:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-131-3},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{150},
  editor =	{Chattopadhyay, Arkadev and Gastin, Paul},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2019.33},
  URN =		{urn:nbn:de:0030-drops-115959},
  doi =		{10.4230/LIPIcs.FSTTCS.2019.33},
  annote =	{Keywords: Pushdown systems, Interval temporal logic, Model checking}
}

Document

DOI: 10.4230/LIPIcs.FSTTCS.2019.34

Taming the Complexity of Timeline-Based Planning over Dense Temporal Domains

Authors: Laura Bozzelli, Angelo Montanari, and Adriano Peron

Published in: LIPIcs, Volume 150, 39th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2019)

Abstract

The problem of timeline-based planning (TP) over dense temporal domains is known to be undecidable. In this paper, we introduce two semantic variants of TP, called strong minimal and weak minimal semantics, which allow to express meaningful properties. Both semantics are based on the minimality in the time distances of the existentially-quantified time events from the universally-quantified reference event, but the weak minimal variant distinguishes minimality in the past from minimality in the future. Surprisingly, we show that, despite the (apparently) small difference in the two semantics, for the strong minimal one, the TP problem is still undecidable, while for the weak minimal one, the TP problem is just PSPACE-complete. Membership in PSPACE is determined by exploiting a strictly more expressive extension (ECA^+) of the well-known robust class of Event-Clock Automata (ECA) that allows to encode the weak minimal TP problem and to reduce it to non-emptiness of Timed Automata (TA). Finally, an extension of ECA^+ (ECA^{++}) is considered, proving that its non-emptiness problem is undecidable. We believe that the two extensions of ECA (ECA^+ and ECA^{++}), introduced for technical reasons, are actually valuable per sé in the field of TA.

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Laura Bozzelli, Angelo Montanari, and Adriano Peron. Taming the Complexity of Timeline-Based Planning over Dense Temporal Domains. In 39th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 150, pp. 34:1-34:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{bozzelli_et_al:LIPIcs.FSTTCS.2019.34,
  author =	{Bozzelli, Laura and Montanari, Angelo and Peron, Adriano},
  title =	{{Taming the Complexity of Timeline-Based Planning over Dense Temporal Domains}},
  booktitle =	{39th IARCS Annual Conference on Foundations of Software Technology and Theoretical Computer Science (FSTTCS 2019)},
  pages =	{34:1--34:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-131-3},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{150},
  editor =	{Chattopadhyay, Arkadev and Gastin, Paul},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.FSTTCS.2019.34},
  URN =		{urn:nbn:de:0030-drops-115963},
  doi =		{10.4230/LIPIcs.FSTTCS.2019.34},
  annote =	{Keywords: Timeline-based planning, timed automata, event-clock automata}
}

Document

DOI: 10.4230/LIPIcs.TIME.2019.17

Synthesis of LTL Formulas from Natural Language Texts: State of the Art and Research Directions

Authors: Andrea Brunello, Angelo Montanari, and Mark Reynolds

Published in: LIPIcs, Volume 147, 26th International Symposium on Temporal Representation and Reasoning (TIME 2019)

Abstract

Linear temporal logic (LTL) is commonly used in model checking tasks; moreover, it is well-suited for the formalization of technical requirements. However, the correct specification and interpretation of temporal logic formulas require a strong mathematical background and can hardly be done by domain experts, who, instead, tend to rely on a natural language description of the intended system behaviour. In such situations, a system that is able to automatically translate English sentences into LTL formulas, and vice versa, would be of great help. While the task of rendering an LTL formula into a more readable English sentence may be carried out in a relatively easy way by properly parsing the formula, the converse is still an open problem, due to the inherent difficulty of interpreting free, natural language texts. Although several partial solutions have been proposed in the past, the literature still lacks a critical assessment of the work done. We address such a shortcoming, presenting the current state of the art for what concerns the English-to-LTL translation problem, and outlining some possible research directions.

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Andrea Brunello, Angelo Montanari, and Mark Reynolds. Synthesis of LTL Formulas from Natural Language Texts: State of the Art and Research Directions. In 26th International Symposium on Temporal Representation and Reasoning (TIME 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 147, pp. 17:1-17:19, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{brunello_et_al:LIPIcs.TIME.2019.17,
  author =	{Brunello, Andrea and Montanari, Angelo and Reynolds, Mark},
  title =	{{Synthesis of LTL Formulas from Natural Language Texts: State of the Art and Research Directions}},
  booktitle =	{26th International Symposium on Temporal Representation and Reasoning (TIME 2019)},
  pages =	{17:1--17:19},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-127-6},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{147},
  editor =	{Gamper, Johann and Pinchinat, Sophie and Sciavicco, Guido},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TIME.2019.17},
  URN =		{urn:nbn:de:0030-drops-113756},
  doi =		{10.4230/LIPIcs.TIME.2019.17},
  annote =	{Keywords: Evolutionary algorithms, Machine learning, Natural language processing, Semantic parsing, Temporal logic}
}

Document

DOI: 10.4230/LIPIcs.TIME.2019.18

Complexity Analysis of a Unifying Algorithm for Model Checking Interval Temporal Logic

Authors: Laura Bozzelli, Angelo Montanari, and Adriano Peron

Published in: LIPIcs, Volume 147, 26th International Symposium on Temporal Representation and Reasoning (TIME 2019)

Abstract

The model-checking (MC) problem of Halpern and Shoham Interval Temporal Logic (HS) has been recently investigated in some papers and is known to be decidable. An intriguing open question concerns the exact complexity of the problem for full HS: it is at least EXPSPACE-hard, while the only known upper bound is non-elementary and is obtained by exploiting an abstract representation of Kripke structure paths called descriptors. In this paper we generalize the approach by providing a uniform framework for model-checking full HS and meaningful (almost maximal) fragments, where a specialized type of descriptor is defined for each fragment. We then devise a general MC alternating algorithm parameterized by the type of descriptor which has a polynomially bounded number of alternations and whose running time is bounded by the length of minimal representatives of descriptors (certificates). We analyze the time complexity of the algorithm and give, by non-trivial arguments, tight bounds on the length of certificates. For two types of descriptors, we obtain exponential upper and lower bounds which lead to an elementary MC algorithm for the related HS fragments. For the other types of descriptors, we provide non-elementary lower bounds. This last result addresses a question left open in some papers regarding the possibility of fixing an elementary upper bound on the size of the descriptors for full HS.

Cite as

Laura Bozzelli, Angelo Montanari, and Adriano Peron. Complexity Analysis of a Unifying Algorithm for Model Checking Interval Temporal Logic. In 26th International Symposium on Temporal Representation and Reasoning (TIME 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 147, pp. 18:1-18:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{bozzelli_et_al:LIPIcs.TIME.2019.18,
  author =	{Bozzelli, Laura and Montanari, Angelo and Peron, Adriano},
  title =	{{Complexity Analysis of a Unifying Algorithm for Model Checking Interval Temporal Logic}},
  booktitle =	{26th International Symposium on Temporal Representation and Reasoning (TIME 2019)},
  pages =	{18:1--18:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-127-6},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{147},
  editor =	{Gamper, Johann and Pinchinat, Sophie and Sciavicco, Guido},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TIME.2019.18},
  URN =		{urn:nbn:de:0030-drops-113768},
  doi =		{10.4230/LIPIcs.TIME.2019.18},
  annote =	{Keywords: Interval temporal logic, Model checking, Complexity and succinctness issues}
}

Document

DOI: 10.4230/LIPIcs.TIME.2018.13

A Game-Theoretic Approach to Timeline-Based Planning with Uncertainty

Authors: Nicola Gigante, Angelo Montanari, Marta Cialdea Mayer, Andrea Orlandini, and Mark Reynolds

Published in: LIPIcs, Volume 120, 25th International Symposium on Temporal Representation and Reasoning (TIME 2018)

Abstract

In timeline-based planning, domains are described as sets of independent, but interacting, components, whose behaviour over time (the set of timelines) is governed by a set of temporal constraints. A distinguishing feature of timeline-based planning systems is the ability to integrate planning with execution by synthesising control strategies for flexible plans. However, flexible plans can only represent temporal uncertainty, while more complex forms of nondeterminism are needed to deal with a wider range of realistic problems. In this paper, we propose a novel game-theoretic approach to timeline-based planning problems, generalising the state of the art while uniformly handling temporal uncertainty and nondeterminism. We define a general concept of timeline-based game and we show that the notion of winning strategy for these games is strictly more general than that of control strategy for dynamically controllable flexible plans. Moreover, we show that the problem of establishing the existence of such winning strategies is decidable using a doubly exponential amount of space.

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Nicola Gigante, Angelo Montanari, Marta Cialdea Mayer, Andrea Orlandini, and Mark Reynolds. A Game-Theoretic Approach to Timeline-Based Planning with Uncertainty. In 25th International Symposium on Temporal Representation and Reasoning (TIME 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 120, pp. 13:1-13:17, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{gigante_et_al:LIPIcs.TIME.2018.13,
  author =	{Gigante, Nicola and Montanari, Angelo and Cialdea Mayer, Marta and Orlandini, Andrea and Reynolds, Mark},
  title =	{{A Game-Theoretic Approach to Timeline-Based Planning with Uncertainty}},
  booktitle =	{25th International Symposium on Temporal Representation and Reasoning (TIME 2018)},
  pages =	{13:1--13:17},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-089-7},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{120},
  editor =	{Alechina, Natasha and N{\o}rv\r{a}g, Kjetil and Penczek, Wojciech},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.TIME.2018.13},
  URN =		{urn:nbn:de:0030-drops-97786},
  doi =		{10.4230/LIPIcs.TIME.2018.13},
  annote =	{Keywords: Timeline-based planning with uncertainty, strategic games, decidability}
}

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