RETRACTED ARTICLE: A multi-agent architectural solution for coherent distributed reconfigurations of function blocks

The paper deals with distributed Multi-Agent Reconfigurable Embedded Control Systems following the International Industrial Standard IEC61499 in which a Function Block (abbreviated by FB) is an event-triggered software component owning data and a control application is a network of distributed blocks that should satisfy functional and temporal properties according to user requirements. We define an architecture of reconfigurable multi-agent systems in which a Reconfiguration Agent is affected to each device of the execution environment to apply local reconfigurations, and a Coordination Agent is proposed for coordinations between devices in order to guarantee safe and adequate distributed reconfigurations. A Communication Protocol is proposed to handle coordinations between agents by using well-defined Coordination Matrices. We specify both reconfiguration agents to be modelled by nested state machines, and the Coordination Agent according to the formalism Net Condition-Event Systems (Abbreviated by NCES) which is an extension of Petri nets. To validate the whole architecture, we check by applying the model checker SESA in each device functional and temporal properties to be described according to the temporal logic “Computation Tree Logic”. We have also to check all possible coordinations between devices by verifying that whenever a reconfiguration is applied in a device, the Coordination Agent and other concerned devices react as described in user requirements. We present a tool applying simulations of this distributed architecture in order to check interactions and reactivities of agents. The paper’s contributions are applied to two Benchmark Production Systems available in our research laboratory.     

Intelligent distributed control systems

ContextThe paper² deals with distributed reconfigurable embedded control systems following the component-based International Industrial Standard IEC61499 in which a Function Block (abbreviated by FB) is an event-triggered software component owning data and a control application is a distributed network of Function Blocks. Nowadays, limited related works have been proposed to address particular cases of reconfigurations without considering distributed architectures. Our first problem is to be able to handle all possible forms of reconfigurations that can be applied at run-time to distributed Function Blocks. In this case, a coordination between devices of the execution environment should be applied to guarantee safe and coherent distributed reconfigurations. A second problem is to find the sufficient solutions for the correct implementation of this reconfigurable distributed architecture.ObjectiveThe paper defines an implementable multi-agent architecture for automatic and coherent reconfigurations of distributed Function Blocks.MethodTo address all possible industrial forms, we classify the reconfiguration scenarios into three levels. The first level deals with additions–removals of Function Blocks to-from the system’s implementation. The second deals with updates of compositions of blocks, and the third deals with updates of data. We define a Reconfiguration Agent for each device of the execution environment, and a unique Coordination Agent for coordinations between devices. Each Reconfiguration Agent to be modelled by nested state machines applies local reconfiguration scenarios in the corresponding device after coordinations with the Coordination Agent. We propose an Inter-Agents Communication Protocol to support correct and coherent reconfigurations of distributed devices. This protocol is based on Coordination Matrices to be handled by the Coordination Agent in order to define all reconfiguration scenarios that should be simultaneously applied in distributed devices. We propose XML-based implementations for both kinds of agents where XML code blocks are exchanged between devices to guarantee safety distributed reconfigurations. The contributions of the paper are applied to two Benchmark Production Systems available in our research laboratory.ResultsThe communication protocol is successfully applied to our platforms where simulations are executed to check distributed and coherent reconfiguration scenarios. The Reconfiguration and Coordination Agents are implemented in this platform by following the International Standard IEC61499. We show in addition XML-based successful interactions between devices when distributed reconfigurations are applied.ConclusionThe paper successfully defines a multi-agent architecture for IEC61499 distributed reconfigurable embedded systems where Coordination and Reconfiguration agents are proposed to allow feasible and coherent distributed reconfigurations by using a defined communication protocol. This architecture is implemented in XML and applied to real industrial platforms.     

Execution models for reconfigurable embedded real‐time systems

This paper deals with the verification and assignment into the execution environment of Reconfigurable Control Applications following the Component‐based International Industrial Standard IEC61499. According to this Standard, a Function Block (FB) is an event‐triggered component and an application is an FB network that has to meet temporal properties according to user requirements. If a reconfiguration scenario is applied at run‐time, then the FB network implementing the application is totally changed or modified. To cover all possible cases, we classify such scenarios into three classes and we define an agent‐based architecture designed with nested state machines to automatically handle all possible reconfigurations. To verify and assign Function Blocks corresponding to each reconfiguration scenario into the execution environment, we define an approach based on the exploration of reachability graphs to verify temporal properties. This approach constructs feasible Operating System tasks encoding the FB network that corresponds to each scenario. Therefore, the application is considered as sets of Operating System (OS) tasks where each set is to load in memory when the corresponding reconfiguration scenario is applied by the agent. We developed the tool X ‐Assign supporting these contributions that we apply on the FESTO production system available in our research laboratory. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

Compositional semantics and behavioral equivalences for P Systems

The aim of the paper is to give a compositional semantics in the style of the Structural Operational Semantics (SOS) and to study behavioral equivalence notions for P Systems. Firstly, we consider P Systems with maximal parallelism and without priorities. We define a process algebra, called P Algebra, whose terms model membranes, we equip the algebra with a Labeled Transition System (LTS) obtained through SOS transition rules, and we study how some equivalence notions defined over the LTS model apply in our case. Then, we consider P Systems with priorities and extend the introduced framework to deal with them. We prove that our compositional semantics reflects correctly maximal parallelism and priorities.     

Enabling run-time composition and support for heterogeneous pervasive multi-agent systems

User needs-driven and computer-supported development of pervasive heterogeneous and dynamic multi-agent systems remains a great challenge for agent research community. This paper presents an innovative approach to composing, validating and supporting multi-agent systems at run-time. Multi-agent systems (MASs) can and should be assembled quasi-automatically and dynamically based on high-level user specifications which are transformed into a shared and common goal–mission. Dynamically generating agents could also be supported as a pervasive service. Heterogeneity of MASs refers to diverse functionality and constituency of the system which include mobile as well as host associated software agents. This paper proposes and demonstrates on-demand and just-in-time agent composition approach which is combined with run-time support for MASs. Run-time support is based on mission cost-efficiency and shared objectives which enable termination, generation, injection and replacement of software agents as the mission evolves at run-time. We present the formal underpinning of our approach and describe the prototype tool – called eHermes, which has been implemented using available agent platforms. Analysis and results of evaluating eHermes are presented and discussed.     

Supporting UML-based development of embedded systems by formal techniques

We describe an approach to support UML-based development of embedded systems by formal techniques. A subset of UML is extended with timing annotations and given a formal semantics. UML models are translated, via XMI, to the input format of formal tools, to allow timed and non-timed model checking and interactive theorem proving. Moreover, the Play-Engine tool is used to execute and analyze requirements by means of live sequence charts. We apply the approach to a part of an industrial case study, the MARS system, and report about the experiences, results and conclusions. This work has been supported by EU-project IST 33522 – OMEGA “Correct Development of Real-Time Embedded Systems in UML”. For more information, see . During this project, the second author was at theWeizmann Institute of Science, the third author at VERIMAG, the fourth author at OFFIS, and the fifth author at NLR.     

Prototyping Dynamic Software Product Lines to evaluate run-time reconfigurations

Dynamic Software Product Lines (DSPL) encompass systems that are capable of modifying their own behavior with respect to changes in their operating environment by using run-time reconfigurations. A failure in these reconfigurations can directly impact the user experience since the reconfigurations are performed when the system is already under the users control. In this work, we prototype a Smart Hotel DSPL to evaluate the reliability-based risk of the DSPL reconfigurations, specifically, the probability of malfunctioning (Availability) and the consequences of malfunctioning (Severity). This DSPL prototype was performed with the participation of human subjects by means of a Smart Hotel case study which was deployed with real devices. Moreover, we successfully identified and addressed two challenges associated with the involvement of human subjects in DSPL prototyping: enabling participants to (1) trigger the run-time reconfigurations and to (2) understand the effects of the reconfigurations. The evaluation of the case study reveals positive results regarding both Availability and Severity. However, the participant feedback highlights issues with recovering from a failed reconfiguration or a reconfiguration triggered by mistake. To address these issues, we discuss some guidelines learned in the case study. Finally, although the results achieved by the DSPL may be considered satisfactory for its particular domain, DSPL engineers must provide users with more control over the reconfigurations or the users will not be comfortable with DSPLs.     

TIGUKAT: A uniform behavioral objectbase management system

We describe the TIGUKAT objectbase management system, which is under development at the Laboratory for Database Systems Research at the University of Alberta. TIGUKAT has a novel object model, whose identifying characteristics include a purely behavioral semantics and a uniform approach to objects. Everything in the system, including types, classes, collections, behaviors, and functions, as well as meta-information, is a first-class object with well-defined behavior. In this way, the model abstracts everything, including traditional structural notions such as instance variables, method implementation, and schema definition, into a uniform semantics of behaviors on objects. Our emphasis in this article is on the object model, its implementation, the persistence model, and the query language. We also (briefly) present other database management functions that are under development such as the query optimizer, the version control system, and the transaction manager.Bell Northem Research     

Adaptive decision-making frameworks for dynamic multi-agent organizational change

This article presents a capability called Adaptive Decision-Making Frameworks (ADMF) and shows that it can result in significantly improved system performance across run-time situation changes in a multi-agent system. Specifically, ADMF can result in improved and more robust performance compared to the use of a single static decision-making framework (DMF). The ADMF capability allows agents to dynamically adapt the DMF in which they participate to fit their run-time situation as it changes. A DMF identifies a set of agents and specifies the distribution of decision-making control and the authority to assign subtasks among these agents as they determine how a goal or set of goals should be achieved. The ADMF capability is a form of organizational adaptation and differs from previous approaches to organizational adaptation and dynamic coordination in that it is the first to allow dynamic and explicit manipulation of these DMF characteristics at run-time as variables controlling agent behavior. The approach proposed for selecting DMFs at run-time parameterizes all domain-specific knowledge as characteristics of the agents’ situation, so the approach is application-independent. The presented evaluation empirically shows that, for at least one multi-agent system, there is no one best DMF for multiple agents across run-time situational changes. Next, it motivates the further exploration of ADMF by showing that adapting DMFs to run-time variations in situation can result in improved overall system performance compared to static or random DMFs.     

Effective intervals determined by information granules to improve forecasting in fuzzy time series

Partitioning the universe of discourse and determining effective intervals are critical for forecasting in fuzzy time series. Equal length intervals used in most existing literatures are convenient but subjective to partition the universe of discourse. In this paper, we study how to partition the universe of discourse into intervals with unequal length to improve forecasting quality. First, we calculate the prototypes of data using fuzzy clustering, then form some subsets according to the prototypes. An unequal length partitioning method is proposed. We show that these intervals carry well-defined semantics. To verify the suitability and effectiveness of the approach, we apply the proposed method to forecast enrollment of students of Alabama University and Germany’s DAX stock index monthly values. Empirical results show that the unequal length partitioning can greatly improve forecast accuracy. Further more, the proposed method is very robust and stable for forecasting in fuzzy time series.     

WebWork: METEOR2's Web-Based Workflow Management System

METEOR₂ workflow management systems consist of both (1) design/build-time and (2) run-time/enactment components for implementing workflow applications. An enactment system provides the command, communication and control for the individual tasks in the workflow. Tasks are the run-time instances of intra- or inter-enterprise applications. We are developing three implementations of the METEOR₂ model: WebWork, OrbWork and NeoWork. This paper discusses WebWork, an implementation relying solely on Web technology as the infrastructure for the enactment system. WebWork supports a distributed implementation with participation of multiple Web servers. It also supports automatic code generation of workflow applications from design specifications produced by a comprehensive graphical designer. WebWork has been developed as a complement of its more heavyweight counterparts (OrbWork and NeoWork), with the goal of providing ease of workflow application development, installation, use and maintenance. At the time of this writing, WebWork has been installed by several of the LSDIS Lab's industrial partners for testing, evaluation and building workflow applications.     

Run-Time Validation of Speculative Optimizations using CVC.

Translation validation is an approach for validating the output of optimizing compilers. Rather than verifying the compiler itself, translation validation mandates that every run of the compiler generate a formal proof that the produced target code is a correct implementation of the source code. Speculative loop optimizations are aggressive optimizations which are only correct under certain conditions which cannot be validated at compile time. We propose using an automatic theorem prover together with the translation validation framework to automatically generate run-time tests for such speculative optimizations. This run-time validation approach must not only detect the conditions under which an optimization generates incorrect code, but also provide a way to recover from the optimization without aborting the program or producing an incorrect result. In this paper, we apply the run-time validation technique to a class of speculative reordering transformations and give some initial results of run-time tests generated by the theorem prover CVC.     

X-Ability: a theory of replication

Summary.   Different replication algorithms provide different solutions to the same basic problem. However, there is no precise specification of the problem itself, only of particular classes of solutions, such as active replication and primary-backup. Having a precise specification of the problem would help us better understand the space of possible solutions and possibly come out with new ones. We present a formal definition of the problem solved by replication in the form of a correctness criterion called x-ability (exactly-once ability). An x-able service has obligations to its environment and its clients. It must update its environment under exactly-once semantics. Furthermore, it must provide idempotent, non-blocking request processing and deliver consistent results to its clients. We illustrate the value of x-ability through a novel replication protocol that handles non-determinism and external side-effects. The replication protocol is asynchronous in the sense that it may vary, at run-time and according to the asynchrony of the system, between some form of primary-backup and some form of active replication. Received: December 2000 / Accepted: September 2001     

Implicit ownership types for memory management

The Real-time Specification for Java (RTSJ) introduced a range of language features for explicit memory management. While the RTSJ gives programmers fine control over memory use and allows linear allocation and constant-time deallocation, the RTSJ relies upon dynamic runtime checks for safety, making it unsuitable for safety critical applications. We introduce ScopeJ, a statically-typed, multi-threaded, object calculus in which scopes are first class constructs. Scopes reify allocation contexts and provide a safe alternative to automatic memory management. Safety follows from the use of an ownership type system that enforces a topology on run-time patterns of references. ScopeJ’s type system is novel in that ownership annotations are implicit. This substantially reduces the burden for developers and increases the likelihood of adoption. The notion of implicit ownership is particularly appealing when combined with pluggable type systems, as one can apply different type constraints to different components of an application depending on the requirements without changing the source language. In related work we have demonstrated the usefulness of our approach in the context of highly-responsive systems and stream processing.     

Specification and Verification of Agent Interaction using Social Integrity Constraints

In this paper we propose a logic-based social approach to the specification and verification of agent interaction. We firstly introduce integrity constraints about social acts (called Social Integrity Constraints) as a formalism to express interaction protocols and to give a social semantics to the behavior of agents, focusing on communicative acts. Then, we discuss several possible kinds of verification of agent interaction, and we show how social integrity constraints can be used to verify some properties in this respect. We focus our attention on static verification of compliance of agent specifications to interaction protocols, and on run-time verification, based on agents' observable behavior. We adopt as a running example the NetBill security transaction protocol for the selling and delivery of information goods.     

Semantics for consistent activation in context-oriented systems

ContextContext-oriented programming languages provide dedicated programming abstractions to define behavioral adaptations and means to combine those adaptations dynamically according to sensed context changes. Some of these languages feature programming abstractions to explicitly define interaction dependencies among contexts. However, the semantics of context activation and the meaning of dependency relations have been described only informally, which in some cases has led to incorrect specifications, faulty implementations and inconsistent system behavior.ObjectiveWith the aim of avoiding faulty implementations and inconsistencies during system execution, this paper proposes both a formal and run-time model of contexts, context activation and context interaction.MethodAs a formal and computational basis, we introduce context Petri nets, a model based on Petri nets, which we found to match closely the structure of contexts in context-oriented systems. The operational semantics of Petri nets permits the modeling of run-time context activations. Existing Petri net analyses allow us to reason about system properties. As validation, we carried out small and medium-sized case studies.ResultsIn the cases explored, context Petri nets served effectively as underlying run-time model to ensure that declared context interaction constraints remain consistent during context manipulation. Moreover, context Petri nets enabled us to analyze certain properties regarding the activation state of particular contexts.ConclusionContext Petri nets thus proved to be appropriate to encode and manage the semantics of context activation, both formally and computationally, so as to preserve the consistency of context-oriented systems.     

Model-based cache-aware dispatching of object-oriented software for multicore systems

In recent years, processor technology has evolved towards multicore processors, which include multiple processing units (cores) in a single package. Those cores, having their own private caches, often share a higher level cache memory dedicated to each processor die. This multi-level cache hierarchy in multicore processors raises the importance of cache utilization problem. Assigning parallel-running software components with common data to processor cores that do not share a common cache increases the number of cache misses. In this paper we present a novel approach that uses model-based information to guide the OS scheduler in assigning appropriate core affinities to software objects at run-time. We build graph models of software and cache hierarchies of processors and devise a graph matcher algorithm that provides mapping between these two graphs. Using this mapping we obtain candidate core sets that each software object can be affiliated with at run-time. These affiliations are determined based on the idea that software components that have the potential to share common data at run-time should run on cores that share a common cache. We also develop an object dispatcher algorithm that keeps track of object affiliations at run-time and dispatches objects by using the information from the compile-time graph matcher. We apply our approach on design pattern implementations and two different application program running on servers using CFS scheduling. Our results show that cache-aware dispatching based on information obtained from software model, decreases number of cache misses significantly and improves CFS’ scheduling performance.