Formal analysis for real-time scheduling

Real-time multi-factory scheduling in Industry 4.0 with virtual alliances

We introduce an open meta-model that will be easily enriched to cover new real-time scheduling models and techniques. On the one hand, it will be possible to connect several independent schedulability analysis tools, following closely the advances in real-time scheduling theory, dealing with a temporal model that will be covered by our metamodel. On the other hand, we will use model transformation techniques in order to extract information from different design methodologies. This extraction can be done at different stages of the design (early for sensitivity analysis, at a later stage for temporal validation) to create a temporal model of the designed system, without the designer to be an expert in scheduling theory. We are working currently on the meta-model phase. The objective is to cover enough concepts to be able to represent a big part of the real-time scheduling models and problems, without introducing too much complexity. This paper uses the UML profile mechanism to describe such a meta-model.

Formal methods encompass a wide choice of techniques and tools for the specification, development, analysis, and verification of software and hardware systems. Formal methods are widely applied in industry, in activities ranging from the elicitation of requirements and the early design phases all the way to the deployment, configuration, and runtime monitoring of actual systems. Formal methods allow one to precisely specify the environment in which a system operates, the requirements and properties that the system should satisfy, the models of the system used during the various design steps, and the code embedded in the final implementation, as well as to express conformance relations between these specifications. We present a broad scope of successful applications of formal methods in industry, not limited to the well-known success stories from the safety-critical domain, like railways and other transportation systems, but also covering other areas such as lithography manufacturing and cloud security in e-commerce, to name but a few. We also report testimonies from a number of representatives from industry who, either directly or indirectly, use or have used formal methods in their industrial project endeavours. These persons are spread geographically, including Europe, Asia, North and South America, and the involved projects witness the large coverage of applications of formal methods, not limited to the safety-critical domain. We thus make a case for the importance of formal methods, and in particular of the capacity to abstract and mathematical reasoning that are taught as part of any formal methods course. These are fundamental Computer Science skills that graduates should profit from when working as computer scientists in industry, as confirmed by industry representatives.

The formal modeling method can accurately describe systems. Using formal method to test software improves the efficiency of software testing and it is comprehensive. Common real-time embedded software formal testing methods include Z language, finite state machine (FSM) and unified modeling language (UML), Petri net and time input/output automata (TIOA). This paper analyzes the characteristics of embedded software testing. The above formal methods and test case coverage criterions and test data collection methods are introduced. Combined with the characteristics of missile-borne software, this paper presents suitable ideas of testing missile-borne software.

Effective ways to optimise real-time pump scheduling to maximise energy efficiency are being sought to meet the challenges in the energy market. However, the considerable number of evaluations of popular optimisation methods based on metaheuristics cause significant delays for real-time pump scheduling, and the simplification of traditional deterministic methods may introduce bias towards the optimal solutions. To address these limitations, an exploration-enhanced deep reinforcement learning (DRL) framework is proposed to address real-time pump scheduling problems in water distribution systems. The experimental results indicate that E-PPO can learn suboptimal scheduling policies for various demand distributions and can control the application time to 0.42 s by transferring the online computation-intensive optimisation task offline. Furthermore, a form of penalty of the tank level was found that can reduce energy costs by up to 11.14% without sacrificing the water level in the long term. Following the DRL framework, the proposed method makes it possible to schedule pumps in a more agile way as a timely response to changing water demand while still controlling the energy cost and level of tanks.

Artificial Intelligence is becoming more attractive to resolve nontrivial problems including the well known real time scheduling (RTS) problem for Embedded Systems (ES). The latter is considered as a hard multi-objective optimization problem because it must optimize at the same time three key conflictual objectives that are tasks deadlines guarantee, energy consumption reduction and reliability enhancement. In this paper, we firstly present the necessary background to well understand the problematic of RTS in the context of ES, then we present our enriched taxonomies for real time, energy and faults tolerance aware scheduling algorithms for ES. After that, we survey the most pertinent existing works of literature targeting the application of AI methods to resolve the RTS problem for ES notably Constraint Programming, Game theory, Machine learning, Fuzzy logic, Artificial Immune Systems, Cellular Automata, Evolutionary algorithms, Multi-agent Systems and Swarm Intelligence. We end this survey by a discussion putting the light on the main challenges and the future directions.

In this paper, we address a one-machine real-time scheduling problem with a continuous input of new jobs subject to time limit constraints. Our aim was to build up an approach that optimizes the execution number of input tasks but which maintains the actual tasks available at the beginning of the processing within their characteristic temporal intervals. We have proposed to solve this problem by constructing a new schedule that accounts for the new circumstances relative to the occurrence of a task arrival. The proposed approach aims at characterizing an insertion position (if any) so as to satisfy the temporal constraints and optimize the criterion. Two algorithms solving such real-time scheduling problem have been elaborated for specific features of the input tasks. Application examples are discussed.

We present a bottom up approach, based on intelligent software agents, to real-time scheduling problems. The approach is market based; the schedule is arrived at through bidding. We recast the real-time scheduling problem as one of allocating, within stipulated deadlines, producer outputs to consumer demands over a time horizon. Producer agents submit bids to consumer agents. These bids are structured as option bids wherein consumer agents pay option premiums to producer agents thereby gaining the ability to postpone commitments. Producer agents use a game theory philosophy called coopetition; that is, they simultaneously compete and cooperate with other producer agents. When they compete, agents use the maximin principle from non-cooperative game theory to devise bidding strategies. When they seek to identify potential partners to coordinate bidding strategies with, agents use the Nash bargaining protocol from cooperative game theory. The framework has a strong positive feedback component in that success breeds success and only the fittest producer agents survive. Agents use memory based reasoning techniques to learn to revise their strategies as games are repeated. Agents are mobile; this enables them to conduct negotiations more efficiently by co-locating to the same machine. Agents are also endowed with limited speech recognition and speech synthesis capabilities; this facilitates interactions with the human decision maker who supervises the entire scheduling process.

Minimizing the CPU power consumption for real time embedded systems is a subject at the confluence of several domains: the conception of embedded systems, the scheduling theory, and the theory of real time operating systems. We are concerned here about the processor(s) power consumption induced by the task execution. We are interested to study real time scheduling theory from the view point of CPU power consumption. This means to add the CPU speed as parameter in the scheduling theory. The mono and multi processors cases are treated unitary. We develop in this paper some results of this extended scheduling theory: necessary and sufficient feasibility condition, globally optimal scheduling, and task distribution on the CPUs for an optimal scheduling from the viewpoint of CPU power consumption.

Multi-agent system consistency-based cooperative scheduling strategy of regional integrated energy system

Real-time vehicle scheduling that can arrange routes variably for the bus within a community in response to new customers’ requests is beneficial to flexible routing for its efficiency in quick response and saving cost especially when the density of customer requests is low. In this paper, a real-time scheduling method for assigning immediate request, which allows variable route, is proposed. A multi-objective model is built for the real-time scheduling problem considering the cost, and passengers on bus and waiting at stops. A two-phase quick response approach and a local optimization method is proposed, which makes trade off between the computation time and the solution quality. A numerical experiment based on the real-world case has been designed to test the effectiveness of the proposed method. Comparison on the variable-route method and the fixed-route approach demonstrates the potential savings and diminishing of waiting time can be obtained through the proposed approach. The method proposed also has potential application for handling real-time vehicle routing in schools, tourist places, and manufactories logistics.

Being rich in the graphical notation, Unified Modeling Language (UML) is regarded as a de facto standard for visualizing, constructing and analyzing the software artifacts in both the domain i.e. in industries as well as in academia. Although UML has numerous good attributes yet not accepted for designing the safety critical system alone. One of the reasons is lack of preciousness in semantic used in graphical model. Consequently, ambiguities are introduced. In case of safety critical system, even a minor ambiguity may cause serious hazards or even loss of life. Therefore there is an utter need of improvement in informality of software models especially in safety critical domain. This paper proposed a framework for verification and validating the dynamic aspect of safety critical system. The proposed framework takes UML sequence diagram of safety critical system as input and refashions this by incorporating Z notation; a formal method. Moreover, this formal model is validated by one of the theorem prover Z notation tool i.e.by Z/EVES.

International audience

In order to analyse extensively the safety of the deployed railway software systems, RATP rely on rigorous verification methodologies based on formal methods. During the past few years, RATP has developed a new formal verification method called PERF, supported by a rich proof tool-chain. The main purpose of this method is to perform a non-intrusive verification on the implemented software. Unlike many formal methodologies, it does not require any intervention in the early stages of the software development.

We consider using hardware and software redundancy to guarantee task deadlines in a hard real-time mu1 tiprocessor system even in the presence of processor failures. A set of scheduling requirements for the real-time fault-tolerant multiprocessor scheduling problem is first identified and a heuristic algorithm is then proposed to solve the problem. Experimental results show that the algorithm finds optimal solutions in most of the cases.