A mobile terminal and a method of controlling a mobile terminal may be provided. The mobile terminal may include a display to display one of a plurality of wallpapers including at least one icon; and a controller to display at least two of the plurality of wallpapers and a plurality of preview screens corresponding to the plurality of wallpapers on the display upon reception of an input of moving at least one icon, moving of the at least one icon being displayed on the displayed wallpapers and preview screens. The mobile terminal can display a movement of icon being displayed on the displayed wallpapers and preview screens. Accordingly, a user may intuitively recognize a location of icon and effectively move a location of icon.

Mobile terminal and method of controlling the same

We describe the extension of a reactive programming language with a behavioral contract construct. It is dedicated to the programming of reactive control of applications in embedded systems, and involves principles of the supervisory control of discrete event systems. Our contribution is in a language approach where modular discrete controller synthesis (DCS) is integrated, and it is concretized in the encapsulation of DCS into a compilation process. From transition system specifications of possible behaviors, DCS automatically produces controllers that make the controlled system satisfy the property given as objective. Our language features and compiling technique provide correctness-by-construction in that sense, and enhance reliability and verifiability. Our application domain is adaptive and reconfigurable systems: closed-loop adaptation mechanisms enable flexible execution of functionalities w.r.t. changing resource and environment conditions. Our language can serve programming such adaption controllers. This paper particularly describes the compilation of the language. We present a method for the modular application of discrete controller synthesis on synchronous programs, and its integration in the BZR language. We consider structured programs, as a composition of nodes, and first apply DCS on particular nodes of the program, in order to reduce the complexity of the controller computation; then, we allow the abstraction of parts of the program for this computation; and finally, we show how to recompose the different controllers computed from different abstractions for their correct co-execution with the initial program. Our work is illustrated with examples, and we present quantitative results about its implementation.

/pdf/contracts-for-modular-discrete-controller-synthesis-1v0vcpr968.pdf

Contracts for modular discrete controller synthesis

The pervasiveness and growing complexity of software systems are challenging software engineering to design systems that can adapt their behavior to withstand unpredictable, uncertain, and continuously changing execution environments. Control theoretical adaptation mechanisms have received growing interest from the software engineering community in the last few years for their mathematical grounding, allowing formal guarantees on the behavior of the controlled systems. However, most of these mechanisms are tailored to specific applications and can hardly be generalized into broadly applicable software design and development processes.This article discusses a reference control design process, from goal identification to the verification and validation of the controlled system. A taxonomy of the main control strategies is introduced, analyzing their applicability to software adaptation for both functional and nonfunctional goals. A brief extract on how to deal with uncertainty complements the discussion. Finally, the article highlights a set of open challenges, both for the software engineering and the control theory research communities.

/pdf/control-strategies-for-self-adaptive-software-systems-39lhxtycc2.pdf

Control Strategies for Self-Adaptive Software Systems

Discrete controller synthesis (DCS) is a formal approach, based on the same state-space exploration algorithms as model-checking. Its interest lies in the ability to obtain automatically systems satisfying by construction formal properties specified a priori. In this paper, our aim is to demonstrate the feasibility of this approach for fault tolerance. We start with a fault intolerant program, modeled as the synchronous parallel composition of finite labeled transition systems; we specify formally a fault hypothesis; we state some fault tolerance requirements; and we use DCS to obtain automatically a program, having the same behavior as the initial fault intolerant one in the absence of faults, and satisfying the fault tolerance requirements under the fault hypothesis. Our original contribution resides in the demonstration that DCS can be elegantly used to design fault tolerant systems, with guarantees on key properties of the obtained system, such as the fault tolerance level, the satisfaction of quantitative constraints, and so on. We show with numerous examples taken from case studies that our method can address different kinds of failures (crash, value, or Byzantine) affecting different kinds of hardware components (processors, communication links, actuators, or sensors). Besides, we show that our method also offers an optimality criterion very useful to synthesize fault tolerant systems compliant to the constraints of embedded systems, like power consumption.

/pdf/automating-the-addition-of-fault-tolerance-with-discrete-3ig9id52nt.pdf

Automating the addition of fault tolerance with discrete controller synthesis

We present interface models that describe both the input assumptions of a component, and its output behavior. By enabling us to check that the input assumptions of a component are met in a design, interface models provide a compatibility check for component-based design. When refining a design into an implementation, interface models require that the output behavior of a component satisfies the design specification only when the input assumptions of the specification are satisfied, yielding greater flexibility in the choice of implementations. Technically, our interface models are games between two players, Input and Output; the duality of the players accounts for the dual roles of inputs and outputs in composition and refinement. We present two interface models in detail, one for a simple synchronous form of interaction between components typical in hardware, and the other for more complex synchronous interactions on bidirectional connections. As an example, we specify the interface of a bidirectional bus, with the input assumption that at any time at most one component has write access to the bus. For these interface models, we present algorithms for compatibility and refinement checking, and we describe efficient symbolic implementations.

Synchronous and bidirectional component interfaces

We define a mixed imperative/declarative programming language: declarative contracts are enforced upon imperatively described behaviors. This paper describes the semantics of the language, making use of the notion of Discrete Controller Synthesis (DCS). We target the application domain of adaptive and reconfigurable systems: our language can serve programming closed-loop adaptation controllers, enabling flexible execution of functionalities w.r.t. changing resource and environment conditions. DCS is integrated into a1 programming language compiler, which facilitates its use by users and programmers, performing executable code generation. The tool is concretely built upon the basis of a reactive programming language compiler, where the nodes describe behaviors that can be modeled in terms of transition systems. Our compiler integrates this with a DCS tool, making it a new environment for formal methods. We define the trace semantics of our contracts language, describe its compilation and establish its correctness, and discuss implementation and examples.

/pdf/integrating-discrete-controller-synthesis-into-a-reactive-3i420jtm2e.pdf

Integrating discrete controller synthesis into a reactive programming language compiler

Event-Condition-Action ECA rules are a widely used language for the high level specification of controllers in adaptive systems, such as Cyber-Physical Systems and smart environments, where devices equipped with sensors and actuators are controlled according to a set of rules. The evaluation and execution of every ECA rule is considered to be independent from the others, but interactions of rule actions can cause the system behaviors to be unpredictable or unsafe. Typical problems are in redundancy of rules, inconsistencies, circularity, or application-dependent safety issues. Hence, there is a need for coordination of ECA rule-based systems in order to ensure safety objectives. We propose a tool-supported method for verifying and controlling the correct interactions of rules, relying on formal models related to reactive systems, and Discrete Controller Synthesis DCS to generate correct rule controllers.

/pdf/coordination-of-eca-rules-by-verification-and-control-vqy63ov74a.pdf

Coordination of ECA Rules by Verification and Control

We present a technique for designing reconfiguration controllers in the Fractal component-based framework. We obtain discrete control loops that automatically enforce safety properties on the interactions between components, concerning, e.g., mutual exclusions, forbidden or imposed sequences. We use a reactive programming language, with a new mechanism of behavioural contracts. Its compilation involves discrete controller synthesis, which automatically generates the correct adaptation controllers. We apply our approach to the problem of adaptive ressource management, illustrated by the example of a HTTP server.

http://pop-art.inrialpes.fr/people/delaval/pub/delaval-cbse10.pdf

Reactive model-based control of reconfiguration in the fractal component-based model

We propose a simple programming language, called Nemo, specific to the domain of multitask real-time control systems, such as in robotic, automotive, or avionics systems. It can be used to specify a set of resources with usage constraints, a set of tasks that consume them according to various modes, and applications sequencing the tasks. We automatically obtain an application-specific task handler that correctly manages the constraints (if there exists one), through a compilation-like process including a phase of discrete controller synthesis. This way, this formal technique contributes to the safety of the designed systems, while being encapsulated in a tool that makes it usable by application experts. Our approach is based on the synchronous modelling techniques, languages, and tools.

/pdf/a-domain-specific-language-for-multitask-systems-applying-1ju04buia2.pdf

Gwenaël Delaval

Papers

Contracts for modular discrete controller synthesis

Integrating discrete controller synthesis into a reactive programming language compiler

Coordination of ECA Rules by Verification and Control

Reactive model-based control of reconfiguration in the fractal component-based model

A Domain-Specific Language for Multitask Systems, Applying Discrete Controller Synthesis