46,423 research outputs found
Conformance Testing as Falsification for Cyber-Physical Systems
In Model-Based Design of Cyber-Physical Systems (CPS), it is often desirable
to develop several models of varying fidelity. Models of different fidelity
levels can enable mathematical analysis of the model, control synthesis, faster
simulation etc. Furthermore, when (automatically or manually) transitioning
from a model to its implementation on an actual computational platform, then
again two different versions of the same system are being developed. In all
previous cases, it is necessary to define a rigorous notion of conformance
between different models and between models and their implementations. This
paper argues that conformance should be a measure of distance between systems.
Albeit a range of theoretical distance notions exists, a way to compute such
distances for industrial size systems and models has not been proposed yet.
This paper addresses exactly this problem. A universal notion of conformance as
closeness between systems is rigorously defined, and evidence is presented that
this implies a number of other application-dependent conformance notions. An
algorithm for detecting that two systems are not conformant is then proposed,
which uses existing proven tools. A method is also proposed to measure the
degree of conformance between two systems. The results are demonstrated on a
range of models
A Compass to Controlled Graph Rewriting
With the growing complexity and autonomy of software-intensive systems, abstract modeling to study and formally analyze those systems is gaining on importance. Graph rewriting is an established, theoretically founded formalism for the graphical modeling of structure and behavior of complex systems. A graph-rewriting system consists of declarative rules, providing templates for potential changes in the modeled graph structures over time. Nowadays complex software systems, often involving distributedness and, thus, concurrency and reactive behavior, pose a challenge to the hidden assumption of global knowledge behind graph-based modeling; in particular, describing their dynamics by rewriting rules often involves a need for additional control to reflect algorithmic system aspects. To that end, controlled graph rewriting has been proposed, where an external control language guides the sequence in which rules are applied. However, approaches elaborating on this idea so far either have a practical, implementational focus without elaborating on formal foundations, or a pure input-output semantics without further considering concurrent and reactive notions.
In the present thesis, we propose a comprehensive theory for an operational semantics of controlled graph rewriting, based on well-established notions from the theory of process calculi. In the first part, we illustrate the aforementioned fundamental phenomena by means of a simplified model of wireless sensor networks (WSN). After recapitulating the necessary background on DPO graph rewriting, the formal framework used throughout the thesis, we present an extensive survey on the state of the art in controlled graph rewriting, along the challenges which we address in the second part where we elaborate our theoretical contributions. As a novel approach, we propose a process calculus for controlled graph rewriting, called RePro, where DPO rule applications are controlled by process terms closely resembling the process calculus CCS. In particular, we address the aforementioned challenges: (i) we propose a formally founded control language for graph rewriting with an operational semantics, (ii) explicitly addressing concurrency and reactive behavior in system modeling, (iii) allowing for a proper handling of process equivalence and action independence using process-algebraic notions.
Finally, we present a novel abstract verification approach for graph rewriting based on abstract interpretation of reactive systems. To that end, we propose the so-called compasses as an abstract representation of infinite graph languages and demonstrate their use for the verification of process properties over infinite input sets
A Taxonomy of Causality-Based Biological Properties
We formally characterize a set of causality-based properties of metabolic
networks. This set of properties aims at making precise several notions on the
production of metabolites, which are familiar in the biologists' terminology.
From a theoretical point of view, biochemical reactions are abstractly
represented as causal implications and the produced metabolites as causal
consequences of the implication representing the corresponding reaction. The
fact that a reactant is produced is represented by means of the chain of
reactions that have made it exist. Such representation abstracts away from
quantities, stoichiometric and thermodynamic parameters and constitutes the
basis for the characterization of our properties. Moreover, we propose an
effective method for verifying our properties based on an abstract model of
system dynamics. This consists of a new abstract semantics for the system seen
as a concurrent network and expressed using the Chemical Ground Form calculus.
We illustrate an application of this framework to a portion of a real
metabolic pathway
Algorithmic Verification of Continuous and Hybrid Systems
We provide a tutorial introduction to reachability computation, a class of
computational techniques that exports verification technology toward continuous
and hybrid systems. For open under-determined systems, this technique can
sometimes replace an infinite number of simulations.Comment: In Proceedings INFINITY 2013, arXiv:1402.661
Counterfactual Causality from First Principles?
In this position paper we discuss three main shortcomings of existing
approaches to counterfactual causality from the computer science perspective,
and sketch lines of work to try and overcome these issues: (1) causality
definitions should be driven by a set of precisely specified requirements
rather than specific examples; (2) causality frameworks should support system
dynamics; (3) causality analysis should have a well-understood behavior in
presence of abstraction.Comment: In Proceedings CREST 2017, arXiv:1710.0277
Weak Quantum Theory: Complementarity and Entanglement in Physics and Beyond
The concepts of complementarity and entanglement are considered with respect
to their significance in and beyond physics. A formally generalized, weak
version of quantum theory, more general than ordinary quantum theory of
material systems, is outlined and tentatively applied to some examples.Comment: Revised version. Chapter 5.2 (old counting) omitted for separate
publication, chapter 5.2 (new counting) reformulate
Design-Time Quantification of Integrity in Cyber-Physical-Systems
In a software system it is possible to quantify the amount of information
that is leaked or corrupted by analysing the flows of information present in
the source code. In a cyber-physical system, information flows are not only
present at the digital level, but also at a physical level, and to and fro the
two levels. In this work, we provide a methodology to formally analyse a
Cyber-Physical System composite model (combining physics and control) using an
information flow-theoretic approach. We use this approach to quantify the level
of vulnerability of a system with respect to attackers with different
capabilities. We illustrate our approach by means of a water distribution case
study
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