1,459 research outputs found
A Temporal Logic for Hyperproperties
Hyperproperties, as introduced by Clarkson and Schneider, characterize the
correctness of a computer program as a condition on its set of computation
paths. Standard temporal logics can only refer to a single path at a time, and
therefore cannot express many hyperproperties of interest, including
noninterference and other important properties in security and coding theory.
In this paper, we investigate an extension of temporal logic with explicit path
variables. We show that the quantification over paths naturally subsumes other
extensions of temporal logic with operators for information flow and knowledge.
The model checking problem for temporal logic with path quantification is
decidable. For alternation depth 1, the complexity is PSPACE in the length of
the formula and NLOGSPACE in the size of the system, as for linear-time
temporal logic
Abstraction in Model Checking Multi-Agent Systems
This thesis presents existential abstraction techniques for multi-agent systems preserving temporal-epistemic
specifications. Multi-agent systems, defined in the interpreted system frameworks,
are abstracted by collapsing the local states and actions of each agent. The goal of abstraction
is to reduce the state space of the system under investigation in order to cope with the state
explosion problem that impedes the verification of very large state space systems. Theoretical
results show that the resulting abstract system simulates the concrete one. Preservation
and correctness theorems are proved in this thesis. These theorems assure that if a temporal-epistemic
formula holds on the abstract system, then the formula also holds on the concrete
one. These results permit to verify temporal-epistemic formulas in abstract systems instead of
the concrete ones, therefore saving time and space in the verification process.
In order to test the applicability, usefulness, suitability, power and effectiveness of the abstraction
method presented, two different implementations are presented: a tool for data-abstraction
and one for variable-abstraction. The first technique achieves a state space reduction by collapsing
the values of the domains of the system variables. The second technique performs a
reduction on the size of the model by collapsing groups of two or more variables. Therefore, the
abstract system has a reduced number of variables. Each new variable in the abstract system
takes values belonging to a new domain built automatically by the tool. Both implementations
perform abstraction in a fully automatic way. They operate on multi agents models specified
in a formal language, called ISPL (Interpreted System Programming Language). This is the
input language for MCMAS, a model checker for multi-agent systems. The output is an ISPL
file as well (with a reduced state space).
This thesis also presents several suitable temporal-epistemic examples to evaluate both techniques.
The experiments show good results and point to the attractiveness of the temporal-epistemic
abstraction techniques developed in this thesis. In particular, the contributions of
the thesis are the following ones:
• We produced correctness and preservation theoretical results for existential abstraction.
• We introduced two algorithms to perform data-abstraction and variable-abstraction on
multi-agent systems.
• We developed two software toolkits for automatic abstraction on multi-agent scenarios:
one tool performing data-abstraction and the second performing variable-abstraction.
• We evaluated the methodologies introduced in this thesis by running experiments on
several multi-agent system examples
Verification of Agent-Based Artifact Systems
Artifact systems are a novel paradigm for specifying and implementing
business processes described in terms of interacting modules called artifacts.
Artifacts consist of data and lifecycles, accounting respectively for the
relational structure of the artifacts' states and their possible evolutions
over time. In this paper we put forward artifact-centric multi-agent systems, a
novel formalisation of artifact systems in the context of multi-agent systems
operating on them. Differently from the usual process-based models of services,
the semantics we give explicitly accounts for the data structures on which
artifact systems are defined. We study the model checking problem for
artifact-centric multi-agent systems against specifications written in a
quantified version of temporal-epistemic logic expressing the knowledge of the
agents in the exchange. We begin by noting that the problem is undecidable in
general. We then identify two noteworthy restrictions, one syntactical and one
semantical, that enable us to find bisimilar finite abstractions and therefore
reduce the model checking problem to the instance on finite models. Under these
assumptions we show that the model checking problem for these systems is
EXPSPACE-complete. We then introduce artifact-centric programs, compact and
declarative representations of the programs governing both the artifact system
and the agents. We show that, while these in principle generate infinite-state
systems, under natural conditions their verification problem can be solved on
finite abstractions that can be effectively computed from the programs. Finally
we exemplify the theoretical results of the paper through a mainstream
procurement scenario from the artifact systems literature
Quantum Simulation Logic, Oracles, and the Quantum Advantage
Query complexity is a common tool for comparing quantum and classical
computation, and it has produced many examples of how quantum algorithms differ
from classical ones. Here we investigate in detail the role that oracles play
for the advantage of quantum algorithms. We do so by using a simulation
framework, Quantum Simulation Logic (QSL), to construct oracles and algorithms
that solve some problems with the same success probability and number of
queries as the quantum algorithms. The framework can be simulated using only
classical resources at a constant overhead as compared to the quantum resources
used in quantum computation. Our results clarify the assumptions made and the
conditions needed when using quantum oracles. Using the same assumptions on
oracles within the simulation framework we show that for some specific
algorithms, like the Deutsch-Jozsa and Simon's algorithms, there simply is no
advantage in terms of query complexity. This does not detract from the fact
that quantum query complexity provides examples of how a quantum computer can
be expected to behave, which in turn has proved useful for finding new quantum
algorithms outside of the oracle paradigm, where the most prominent example is
Shor's algorithm for integer factorization.Comment: 48 pages, 46 figure
07091 Abstracts Collection -- Mobility, Ubiquity and Security
From 25.02.2007 to 02.03.2007, the Dagstuhl Seminar 07091 ``Mobility,
Ubiquity and Security\u27\u27 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
A Cut Principle for Information Flow
We view a distributed system as a graph of active locations with
unidirectional channels between them, through which they pass messages. In this
context, the graph structure of a system constrains the propagation of
information through it.
Suppose a set of channels is a cut set between an information source and a
potential sink. We prove that, if there is no disclosure from the source to the
cut set, then there can be no disclosure to the sink. We introduce a new
formalization of partial disclosure, called *blur operators*, and show that the
same cut property is preserved for disclosure to within a blur operator. This
cut-blur property also implies a compositional principle, which ensures limited
disclosure for a class of systems that differ only beyond the cut.Comment: 31 page
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