990 research outputs found
Process algebra for performance evaluation
This paper surveys the theoretical developments in the field of stochastic process algebras, process algebras where action occurrences may be subject to a delay that is determined by a random variable. A huge class of resource-sharing systems â like large-scale computers, clientâserver architectures, networks â can accurately be described using such stochastic specification formalisms. The main emphasis of this paper is the treatment of operational semantics, notions of equivalence, and (sound and complete) axiomatisations of these equivalences for different types of Markovian process algebras, where delays are governed by exponential distributions. Starting from a simple actionless algebra for describing time-homogeneous continuous-time Markov chains, we consider the integration of actions and random delays both as a single entity (like in known Markovian process algebras like TIPP, PEPA and EMPA) and as separate entities (like in the timed process algebras timed CSP and TCCS). In total we consider four related calculi and investigate their relationship to existing Markovian process algebras. We also briefly indicate how one can profit from the separation of time and actions when incorporating more general, non-Markovian distributions
Computing alignments with constraint programming : the acyclic case
Conformance checking confronts process models with real
process executions to detect and measure deviations between modelled
and observed behaviour. The core technique for conformance checking
is the computation of an alignment. Current approaches for alignment
computation rely on a shortest-path technique over the product of the
state-space of a model and the observed trace, thus suffering from the
well-known state explosion problem. This paper presents a fresh alternative
for alignment computation of acyclic process models, that encodes
the alignment problem as a Constraint Satisfaction Problem. Since modern
solvers for this framework are capable of dealing with large instances,
this contribution has a clear potential. Remarkably, our prototype implementation
can handle instances that represent a real challenge for current
techniques. Main advantages of using Constraint Programming paradigm
lie in the possibility to adapt parameters such as the maximum search
time, or the maximum misalignment allowed. Moreover, using search and
propagation algorithms incorporated in Constraint Programming Solvers
permits to find solutions for problems unsolvable with other techniques.Ministerio de EconomĂa y Competitividad TIN2015-63502-C3-2-RMinisterio de EconomĂa y Competitividad TIN2013-46181-C2-1-
Reasoning about Goal-Plan Trees in Autonomous Agents: Development of Petri net and Constraint-Based Approaches with Resulting Performance Comparisons
Multi-agent systems and autonomous agents are becoming increasingly important in current computing technology. In many applications, the agents are often asked to achieve multiple goals individually or within teams where the distribution of these goals may be negotiated among the agents. It is expected that agents should be capable of working towards achieving all its currently adopted goals concurrently. However, in doing so, the goals can interact both constructively and destructively with each other, so a rational agent must be able to reason about these interactions and any other constraints that may be imposed on them, such as the limited availability of resources that could affect their ability to achieve all adopted goals when pursuing them concurrently. Currently, agent development languages require the developer to manually identify and handle these circumstances.
In this thesis, we develop two approaches for reasoning about the interactions between the goals of an individual agent. The first of these employs Petri nets to represent and reason about the goals, while the second uses constraint satisfaction techniques to find efficient ways of achieving the goals. Three types of reasoning are incorporated into these models: reasoning about consumable resources where the availability of the resources is limited; the constructive interaction of goals whereby a single plan can be used to achieve multiple goals; and the interleaving of steps for achieving different goals that could cause one or more goals to fail.
Experimental evaluation of the two approaches under various different circumstances highlights the benefits of the reasoning developed here whilst also identifying areas where one approach provides better results than the other. This can then be applied to suggest the underlying technique used to implement the reasoning that the agent may want to employ based on the goals it has been assigned
Verifying Modal Workflow Specifications Using Constraint Solving
International audienceNowadaysworkflowsareextensivelyusedbycompaniestoimproveorganizationalefficiencyandproductivity.Thispaperfocusesontheverificationofmodalworkflowspecificationsusingconstraintsolvingasacomputationaltool.ItsmaincontributionconsistsindevelopinganinnovativeformalframeworkbasedonconstraintsystemstomodelexecutionsofworkflowPetrinetsandtheirstructuralproperties,aswellastoverifytheirmodalspecifications.Finally,animplementationandpromisingexperimentalresultsconstituteapracticalcontribution
Symbolic Reachability Analysis of B through ProB and LTSmin
We present a symbolic reachability analysis approach for B that can provide a
significant speedup over traditional explicit state model checking. The
symbolic analysis is implemented by linking ProB to LTSmin, a high-performance
language independent model checker. The link is achieved via LTSmin's PINS
interface, allowing ProB to benefit from LTSmin's analysis algorithms, while
only writing a few hundred lines of glue-code, along with a bridge between ProB
and C using ZeroMQ. ProB supports model checking of several formal
specification languages such as B, Event-B, Z and TLA. Our experiments are
based on a wide variety of B-Method and Event-B models to demonstrate the
efficiency of the new link. Among the tested categories are state space
generation and deadlock detection; but action detection and invariant checking
are also feasible in principle. In many cases we observe speedups of several
orders of magnitude. We also compare the results with other approaches for
improving model checking, such as partial order reduction or symmetry
reduction. We thus provide a new scalable, symbolic analysis algorithm for the
B-Method and Event-B, along with a platform to integrate other model checking
improvements via LTSmin in the future
A mission management system for a fleet of gliders
International audienceThe objective of AGLIMMS project, whose acronym stands for Acoustic GLIders Mission Management System, is to efficiently coordinate a fleet of underwater gliders whose missions are to obtain physical, chemical, biological and/or acoustic measurements on a large 3D sea area. This paper describes planning and supervision functions under development and their integration in a global centralised architecture. A demonstration with three SeaExplorer from Alseamar is planned late 2019
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