281,209 research outputs found
Formal design and verification of a reliable computing platform for real-time control (phase 3 results)
In this paper the design and formal verification of the lower levels of the Reliable Computing Platform (RCP), a fault-tolerant computing system for digital flight control applications, are presented. The RCP uses NMR-style redundancy to mask faults and internal majority voting to flush the effects of transient faults. Two new layers of the RCP hierarchy are introduced: the Minimal Voting refinement (DA_minv) of the Distributed Asynchronous (DA) model and the Local Executive (LE) Model. Both the DA_minv model and the LE model are specified formally and have been verified using the Ehdm verification system. All specifications and proofs are available electronically via the Internet using anonymous FTP or World Wide Web (WWW) access
Model based safety analysis for an Unmanned Aerial System
This paper aims at describing safety architectures of autonomous systems by using Event-B formal method. The autonomous systems combine various activities which can be organised in layers. The Event-B formalism well supports the rigorous design of this kind of systems. Its refinement mechanism allows a progressive modelling by checking the correctness and the relevance of the models by discharging proof obligations. The application of the Event-B method within the framework of layered architecture specification enables the emergence of desired global properties with relation to layer interactions. The safety objectives are derived in each layer and they involve static and dynamic properties such as an independence property, a redundant property or a sequential property. The originality of our approach is to consider a refinement process between two layers in which the abstract model is the model of the lower layer. In our modelling, we distinguish nominal behaviour and abnormal behaviour in order to well establish failure propagation in our architecture
A Model of Layered Architectures
Architectural styles and patterns play an important role in software
engineering. One of the most known ones is the layered architecture style.
However, this style is usually only stated informally, which may cause problems
such as ambiguity, wrong conclusions, and difficulty when checking the
conformance of a system to the style. We address these problems by providing a
formal, denotational semantics of the layered architecture style. Mainly, we
present a sufficiently abstract and rigorous description of layered
architectures. Loosely speaking, a layered architecture consists of a hierarchy
of layers, in which services communicate via ports. A layer is modeled as a
relation between used and provided services, and layer composition is defined
by means of relational composition. Furthermore, we provide a formal definition
for the notions of syntactic and semantic dependency between the layers. We
show that these dependencies are not comparable in general. Moreover, we
identify sufficient conditions under which, in an intuitive sense which we make
precise in our treatment, the semantic dependency implies, is implied by, or
even coincides with the reflexive-transitive closure of the syntactic
dependency. Our results provide a technology-independent characterization of
the layered architecture style, which may be used by software architects to
ensure that a system is indeed built according to that style.Comment: In Proceedings FESCA 2015, arXiv:1503.0437
Simulation of reconstructions of the polar ZnO (0001) surfaces
Surface reconstructions on the polar ZnO(0001) surface are investigated using
empirical potential models. Several possible reconstructions based around
triangular motifs are investigated. The quenching of the dipole moment in the
material dominates the energetics of the surface patterns so that no one
particular size of surface triangular island or pit is strongly favoured. We
employ Monte Carlo simulations to explore which patterns emerge from a high
temperature quench and during deposition of additional ZnO monolayers. The
simulations show that a range of triangular islands and pits evolve in
competition with one another. The surface patterns we discover are
qualitatively similar to those observed experimentally
MORPH: A Reference Architecture for Configuration and Behaviour Self-Adaptation
An architectural approach to self-adaptive systems involves runtime change of
system configuration (i.e., the system's components, their bindings and
operational parameters) and behaviour update (i.e., component orchestration).
Thus, dynamic reconfiguration and discrete event control theory are at the
heart of architectural adaptation. Although controlling configuration and
behaviour at runtime has been discussed and applied to architectural
adaptation, architectures for self-adaptive systems often compound these two
aspects reducing the potential for adaptability. In this paper we propose a
reference architecture that allows for coordinated yet transparent and
independent adaptation of system configuration and behaviour
Leading the Practice in Layered Enterprise Architecture
While Enterprise Architecture (EA) causes organisations to think,
work and model in domains, there are inadequacies in such a waterfall approach.
By restating domains as layers, i.e. LEAD (Layered Enterprise Architecture Design/
Development) based on the LEAD Enterprise Ontology, EA performs better
in enterprise layers and levels of abstraction. Through LEAD, the domain relationships
are also better captured, hence leading the advancement of agile EA
Prototype of Fault Adaptive Embedded Software for Large-Scale Real-Time Systems
This paper describes a comprehensive prototype of large-scale fault adaptive
embedded software developed for the proposed Fermilab BTeV high energy physics
experiment. Lightweight self-optimizing agents embedded within Level 1 of the
prototype are responsible for proactive and reactive monitoring and mitigation
based on specified layers of competence. The agents are self-protecting,
detecting cascading failures using a distributed approach. Adaptive,
reconfigurable, and mobile objects for reliablility are designed to be
self-configuring to adapt automatically to dynamically changing environments.
These objects provide a self-healing layer with the ability to discover,
diagnose, and react to discontinuities in real-time processing. A generic
modeling environment was developed to facilitate design and implementation of
hardware resource specifications, application data flow, and failure mitigation
strategies. Level 1 of the planned BTeV trigger system alone will consist of
2500 DSPs, so the number of components and intractable fault scenarios involved
make it impossible to design an `expert system' that applies traditional
centralized mitigative strategies based on rules capturing every possible
system state. Instead, a distributed reactive approach is implemented using the
tools and methodologies developed by the Real-Time Embedded Systems group.Comment: 2nd Workshop on Engineering of Autonomic Systems (EASe), in the 12th
Annual IEEE International Conference and Workshop on the Engineering of
Computer Based Systems (ECBS), Washington, DC, April, 200
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