562 research outputs found

    LNCS

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    Imprecision in timing can sometimes be beneficial: Metric interval temporal logic (MITL), disabling the expression of punctuality constraints, was shown to translate to timed automata, yielding an elementary decision procedure. We show how this principle extends to other forms of dense-time specification using regular expressions. By providing a clean, automaton-based formal framework for non-punctual languages, we are able to recover and extend several results in timed systems. Metric interval regular expressions (MIRE) are introduced, providing regular expressions with non-singular duration constraints. We obtain that MIRE are expressively complete relative to a class of one-clock timed automata, which can be determinized using additional clocks. Metric interval dynamic logic (MIDL) is then defined using MIRE as temporal modalities. We show that MIDL generalizes known extensions of MITL, while translating to timed automata at comparable cost

    Satisfiability Checking of Multi-Variable TPTL with Unilateral Intervals Is PSPACE-Complete

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    Adamawa primary education research: final report

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    Satisfiability Checking of Multi-Variable TPTL with Unilateral Intervals Is PSPACE-Complete

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    We investigate the decidability of the 0,{0,\infty} fragment of Timed Propositional Temporal Logic (TPTL). We show that the satisfiability checking of TPTL0,^{0,\infty} is PSPACE-complete. Moreover, even its 1-variable fragment (1-TPTL0,^{0,\infty}) is strictly more expressive than Metric Interval Temporal Logic (MITL) for which satisfiability checking is EXPSPACE complete. Hence, we have a strictly more expressive logic with computationally easier satisfiability checking. To the best of our knowledge, TPTL0,^{0,\infty} is the first multi-variable fragment of TPTL for which satisfiability checking is decidable without imposing any bounds/restrictions on the timed words (e.g. bounded variability, bounded time, etc.). The membership in PSPACE is obtained by a reduction to the emptiness checking problem for a new "non-punctual" subclass of Alternating Timed Automata with multiple clocks called Unilateral Very Weak Alternating Timed Automata (VWATA0,^{0,\infty}) which we prove to be in PSPACE. We show this by constructing a simulation equivalent non-deterministic timed automata whose number of clocks is polynomial in the size of the given VWATA0,^{0,\infty}.Comment: Accepted in Concur 202

    Generalizing Non-Punctuality for Timed Temporal Logic with Freeze Quantifiers

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    Metric Temporal Logic (MTL) and Timed Propositional Temporal Logic (TPTL) are prominent real-time extensions of Linear Temporal Logic (LTL). In general, the satisfiability checking problem for these extensions is undecidable when both the future U and the past S modalities are used. In a classical result, the satisfiability checking for MITL[U,S], a non punctual fragment of MTL[U,S], is shown to be decidable with EXPSPACE complete complexity. Given that this notion of non punctuality does not recover decidability in the case of TPTL[U,S], we propose a generalization of non punctuality called \emph{non adjacency} for TPTL[U,S], and focus on its 1-variable fragment, 1-TPTL[U,S]. While non adjacent 1-TPTL[U,S] appears to be be a very small fragment, it is strictly more expressive than MITL. As our main result, we show that the satisfiability checking problem for non adjacent 1-TPTL[U,S] is decidable with EXPSPACE complete complexity

    Bus Tales: Travel-time use, technologies, and journey experiences on the bus

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    Recently there has been a growing interest in the ways in which people use their time during travel, and what different types of value (economic or personal) such ‘travel-time activity’ provides. The activities of public transport passengers have been explored from a number of perspectives, and several of these have been reported to have a positive influence on the experience of the journey. However, within existing research the bus has received almost no specific attention, with most studies focussing on the train. At the same time, there is a stated policy need to improve the attractiveness of bus travel and increase patronage on local bus services in the UK. This thesis draws these strands together, and investigates how the activities in which bus passengers engage on-the-move give meaning to their journeys and help to shape their experiences and perceptions of the mode. In doing so, it considers how a focus on travel-time activity is potentially a valuable way of improving journey experiences for users, and increasing the attractiveness of bus travel to non-users.Identifying the need to explore travel-time activity on the bus, the thesis develops a discussion of what is already known about the ways in which passengers (largely rail passengers) use their time, and how this has been found to influence their experiences and perceptions of the journey. Within this, specific attention is paid to the importance of carried objects and mobile technologies (mobile phones, books, music players, and more) in facilitating travel-time activities. In doing so, this thesis considers how existing travel-time research is relevant to the context of the bus journey. It identifies and addresses three gaps in existing knowledge: (i)It provides the missing link between research which has demonstrated that travel-time activity has the potential to improve journey experiences for public transport passengers, and research which has specifically explored the journey experiences of bus passengers. (ii)It explores the current lack of understanding concerning the ways in which travel-time activities on the bus give meaning to passengers’ experiences of the journey. In particular, there has been little focus on how the travel-time “tools” – the carried objects, mobile technologies, and ICTs – are potentially enabling bus passengers to conduct different activities during travel-time. (iii)It seeks to fill a gap in existing knowledge in terms of specific research into subjectivity of travel-time on the bus, and how it is enacted and experienced differently by different individuals and groups.The thesis follows a three-phase methodology in generating new empirical data on travel-time activity and journey experience on the bus. First, two phases of qualitative data collection were undertaken. This involved a novel online discussion group utilising the popular social networking site “Facebook”. Following this two focus groups were conducted with bus users and car users to explore the qualitative findings in greater depth and inform the construction of the final quantitative phase. This consisted of a large-scale on-board questionnaire survey of 840 bus passengers on five routes in Bristol, UK. Thus the qualitative data provided rich discourses and explanations of passengers’ experience of travel-time, and the quantitative data tested these findings amongst a sample of the wider bus user population.This thesis finds that there are several activities and technologies particularly suited to the bus journey, and that people engage in these for a number of reasons. For example, travel-time activity is sometimes valuable for providing a “slice” of personal time within which to relax or complete personal tasks. For other passengers (or at other times) it helps to mitigate some of the more common negative experiences encountered along the journey such as boredom, stress, and social discomfort. The subjectivity of the passenger is central to explanations of travel-time use on the bus; travel-time is perceived differently by different people and thus is used and experienced in many ways. The thesis pays attention to the tensions that this creates within the collective experience of the journey. In particular the intensely social nature of bus travel is explained as being at the heart of the experience. For some the journey is a chance to socialise, where for others the public spaces of the bus can engender a lack of a sense of personal space and a negative experience.In concluding, the thesis identifies a disparity between the quantitative and qualitative findings. The qualitative data go into depth in explaining the rich, contextual experience of activity, where the quantitative findings focus on the immediate experience and find other factors to be of more primary significance than activity – particularly punctuality, age, and a person’s social disposition. Thus, the thesis contextualises its own findings, highlighting the potential of travel-time activity in increasing the attractiveness of bus travel, whilst at the same time firmly framing the importance of this new knowledge within the wider picture of the bus as a service

    Research on the export mode of sinotruck and future prospect in Africa

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    Revisiting timed logics with automata modalities

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    © 2019 ACM. It is well known that (timed) ω-regular properties such as 'p holds at every even position' and 'p occurs at least three times within the next 10 time units' cannot be expressed in Metric Interval Temporal Logic (MITL) and Event Clock Logic (ECL). A standard remedy to this deficiency is to extend these with modalities defined in terms of automata. In this paper, we show that the logics EMITL0, ∞ (adding non-deterministic finite automata modalities into the fragment of MITL with only lower- and upper-bound constraints) and EECL (adding automata modalities into ECL) are already as expressive as EMITL (full MITL with automata modalities). In particular, the satisfiability and model-checking problems for EMITL0, ∞ and EECL are PSPACE-complete, whereas the same problems for EMITL are EXPSPACE-complete. We also provide a simple translation from EMITL0, ∞ to diagonal-free timed automata, which enables practical satisfiability and model checking based on off-the-shelf tools

    On verifying timed hyperproperties

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    We study the satisfiability and model-checking problems for timed hyperproperties specified with HyperMTL, a timed extension of HyperLTL. Depending on whether interleaving of events in different traces is allowed, two possible semantics can be defined for timed hyperproperties: asynchronous and synchronous. While the satisfiability problem can be decided similarly to HyperLTL regardless of the choice of semantics, we show that the model-checking problem, unless the specification is alternation-free, is undecidable even when very restricted timing constraints are allowed. On the positive side, we show that model checking HyperMTL with quantifier alternations is possible under certain conditions in the synchronous semantics, or when there is a fixed bound on the length of the time domain.EP/K026399/1 and EP/P020011/
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