181,597 research outputs found
Extracting Formal Models from Normative Texts
We are concerned with the analysis of normative texts - documents based on
the deontic notions of obligation, permission, and prohibition. Our goal is to
make queries about these notions and verify that a text satisfies certain
properties concerning causality of actions and timing constraints. This
requires taking the original text and building a representation (model) of it
in a formal language, in our case the C-O Diagram formalism. We present an
experimental, semi-automatic aid that helps to bridge the gap between a
normative text in natural language and its C-O Diagram representation. Our
approach consists of using dependency structures obtained from the
state-of-the-art Stanford Parser, and applying our own rules and heuristics in
order to extract the relevant components. The result is a tabular data
structure where each sentence is split into suitable fields, which can then be
converted into a C-O Diagram. The process is not fully automatic however, and
some post-editing is generally required of the user. We apply our tool and
perform experiments on documents from different domains, and report an initial
evaluation of the accuracy and feasibility of our approach.Comment: Extended version of conference paper at the 21st International
Conference on Applications of Natural Language to Information Systems (NLDB
2016). arXiv admin note: substantial text overlap with arXiv:1607.0148
Implications of climate variability for the detection of multiple equilibria and for rapid transitions in the atmosphere-vegetation system
Paleoclimatic records indicate a decline of vegetation cover in the Western Sahara at the end of the African Humid Period (about 5,500 years before present). Modelling studies have shown that this phenomenon may be interpreted as a critical transition that results from a bifurcation in the atmosphere-vegetation system. However, the stability properties of this system are closely linked to climate variability and depend on the climate model and the methods of analysis. By coupling the Planet Simulator (PlaSim), an atmosphere model of intermediate complexity, with the simple dynamic vegetation model VECODE, we assess previous methods for the detection of multiple equilibria, and demonstrate their limitations. In particular, a stability diagram can yield misleading results because of spatial interactions, and the system's steady state and its dependency on initial conditions are affected by atmospheric variability and nonlinearities. In addition, we analyse the implications of climate variability for the abruptness of a vegetation decline. We find that a vegetation collapse can happen at different locations at different times. These collapses are possible despite large and uncorrelated climate variability. Because of the nonlinear relation between vegetation dynamics and precipitation the green state is initially stabilised by the high variability. When precipitation falls below a critical threshold, the desert state is stabilised as variability is then also decreased. © 2011 The Author(s)
Metamagnetic phase transition in the Ising plus Dzyaloshinskii-Moriya model
We study the 1D ferromagnetic Ising (spin-1/2) model with the
Dzyaloshinskii-Moriya (DM) interaction. We analyze the low energy excitation
spectrum and the ground state magnetic phase diagram using the Lanczos method.
The DM interaction-dependency is calculated for the low-energy excitation
spectrum, spiral order parameter and spin-spin correlation functions. We show
that a metamagnetic quantum phase transition occurs between the ferromagnetic
and spiral phases. The existence of the metamagnetic phase transition is
confirmed, using the variational matrix product states approach.Comment: 5 pages, 6 figure
One-dimensional Particle Processes with Acceleration/Braking Asymmetry
The slow-to-start mechanism is known to play an important role in the
particular shape of the Fundamental diagram of traffic and to be associated to
hysteresis effects of traffic flow.We study this question in the context of
exclusion and queueing processes,by including an asymmetry between deceleration
and acceleration in the formulation of these processes. For exclusions
processes, this corresponds to a multi-class process with transition asymmetry
between different speed levels, while for queueing processes we consider
non-reversible stochastic dependency of the service rate w.r.t the number of
clients. The relationship between these 2 families of models is analyzed on the
ring geometry, along with their steady state properties. Spatial condensation
phenomena and metastability is observed, depending on the level of the
aforementioned asymmetry. In addition we provide a large deviation formulation
of the fundamental diagram (FD) which includes the level of fluctuations, in
the canonical ensemble when the stationary state is expressed as a product form
of such generalized queues.Comment: 28 pages, 8 figure
A Change Support Model for Distributed Collaborative Work
Distributed collaborative software development tends to make artifacts and
decisions inconsistent and uncertain. We try to solve this problem by providing
an information repository to reflect the state of works precisely, by managing
the states of artifacts/products made through collaborative work, and the
states of decisions made through communications. In this paper, we propose
models and a tool to construct the artifact-related part of the information
repository, and explain the way to use the repository to resolve
inconsistencies caused by concurrent changes of artifacts. We first show the
model and the tool to generate the dependency relationships among UML model
elements as content of the information repository. Next, we present the model
and the method to generate change support workflows from the information
repository. These workflows give us the way to efficiently modify the
change-related artifacts for each change request. Finally, we define
inconsistency patterns that enable us to be aware of the possibility of
inconsistency occurrences. By combining this mechanism with version control
systems, we can make changes safely. Our models and tool are useful in the
maintenance phase to perform changes safely and efficiently.Comment: 10 pages, 13 figures, 4 table
An Approach to Select Cost-Effective Risk Countermeasures Exemplified in CORAS
Risk is unavoidable in business and risk management is needed amongst others
to set up good security policies. Once the risks are evaluated, the next step
is to decide how they should be treated. This involves managers making
decisions on proper countermeasures to be implemented to mitigate the risks.
The countermeasure expenditure, together with its ability to mitigate risks, is
factors that affect the selection. While many approaches have been proposed to
perform risk analysis, there has been less focus on delivering the prescriptive
and specific information that managers require to select cost-effective
countermeasures. This paper proposes a generic approach to integrate the cost
assessment into risk analysis to aid such decision making. The approach makes
use of a risk model which has been annotated with potential countermeasures,
estimates for their cost and effect. A calculus is then employed to reason
about this model in order to support decision in terms of decision diagrams. We
exemplify the instantiation of the generic approach in the CORAS method for
security risk analysis.Comment: 33 page
Rewiring strategies for changing environments
A typical pervasive application executes in a changing environment: people, computing resources, software services and network connections come and go continuously. A robust pervasive application needs adapt to this changing context as long as there is an appropriate rewiring strategy that guarantees correct behavior. We combine the MERODE modeling methodology with the ReWiRe framework for creating interactive pervasive applications that can cope with changing environments. The core of our approach is a consistent environment model, which is essential to create (re)configurable context-aware pervasive applications. We aggregate different ontologies that provide the required semantics to describe almost any target environment. We present a case study that shows a interactive pervasive application for media access that incorporates parental control on media content and can migrate between devices. The application builds upon models of the run-time environment represented as system states for dedicated rewiring strategies
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