Autonomic system design based on the integrated use of SSM and VSM

This paper describes an approach to autonomic systems development that involves the integrated use of two general systems design techniques: Soft Systems Methodology (SSM) and the Viable System Model (VSM). The paper summarizes the relevant aspects of each technique and describes how they can be used together to create design models of an autonomic system and its environment. The discussion is illustrated through a consideration of the development of a generic computing system to help manage the technology used in an organisation.     

Properties and calculation of transmission zeros of linear multivariable systems

A new definition of transmission zeros for a linear, multivariable, time-invariant system is made which is shown to be equivalent to previous definitions. Based on this new definition of transmission zeros, new properties of transmission zeros of a system are then obtained; in particular, it is shown that a system with an unequal number of inputs and outputs almost always has no transmission zeros and that a system with an equal number of inputs and outputs almost always has either n−1 or n transmission zeros, where n is the order of the system; transmission zeros of cascade systems are then studied, and it is shown how the transmission zeros of a system relate to the poles of a closed loop system subject to high gain output feedback. An application of transmission zeros to the servomechanism problem is also included. A fast, efficient, numerically stable algorithm is then obtained which enables the transmission zeros of high order multivariable systems to be readily obtained. Some numerical examples for a 9th order system are given to illustrate the algorithm.     

Contract analysis: A performance measures and profit evaluation within two-echelon supply chains

Coordination is regarded as key in managing dependencies between distinctive members of a supply chain through the benefits of coordination mechanisms. Such coordination mechanisms are contracts, implemented to increase total supply chain profit, reduce costs and share risk among supply chain members. However, by contract implementation the retailer is constrained in his purchase by bearing the entire risk of holding the inventory (wholesale price contract) or by limited risk allocated to the supplier (buyback, revenue sharing and quantity flexibility contracts). By implementing an advanced purchase system the risk of inventory is fairly divided between the supplier and the retailer. In order to observe inventory implications on the supply chain bottom line, this article is directed towards the evaluation of performance measures and supply chain profit behavior under buyback, revenue sharing, quantity flexibility and advanced purchase discount contracts versus no coordination and wholesale price systems.     

Production scheduling with subcontracting: the subcontractor’s pricing game

This paper studies a two-stage game with a manufacturer and a subcontractor who are faced by a production scheduling problem. The manufacturer has a set of jobs to process, a subset of which can be subcontracted to the subcontractor to reduce the tardiness cost. In the game, the subcontractor makes the first decision to ask for a unit price of his machine time to be used by the manufacturer, and then the manufacturer follows to decide which jobs to be subcontracted to process and how the production scheduling is made. We analyze the game and derive how the subcontractor can optimize the unit price to maximize his profit. We then investigate the performance of such a simple contract from the viewpoint of coordination, and propose two other contracts that can achieve coordination between the two players.     

Task allocation and the balancing of task demands in the multi-man-machine system--some case studies

Various forms of team organisation are described. These are based on the concepts of vertical and horizontal structure. Task factors of complexity and organisation are introduced and their relationships with various forms of multiman-machine system are discussed. Experimental work is briefly described and then two case study analyses of operational systems are presented. The first, an examination of airport air traffic contol, illustrates how a multiman system can be reorganised to yield a more balanced distribution of task demands. The second, a study of an ambulance control room, shows the implucations for team organisation of a shared computer data-base. These case studies demonstrate that the concepts developed in the laboratory context can be applied to operational multiman-machine systems.     

Using Domain-Independent Exception Handling Services to Enable Robust Open Multi-Agent Systems: The Case of Agent Death

This paper addresses a simple but critical question: how can we create robust multi-agent systems out of the often unreliable agents and infrastructures we can expect to find in open systems contexts? We propose an approach to this problem based on distinct exception handling (EH) services that enact coordination protocol-specific but domain-independent strategies to monitor agent systems for problems (‘exceptions’) and intervene when necessary to avoid or resolve them. The value of this approach is demonstrated for the ‘agent death’ exception in the Contract Net protocol; we show through simulation that the EH service approach provides substantially improved performance compared to existing approaches in a way that is appropriate for open multi-agent systems.     

一种基于双向选择的多Agent系统自动集成方案

多Agent系统集成方案的选择能极大程度地影响多Agent系统的性能。目前大多数的多Agent系统集成方案只关注于系统级的行为与性能。本文在关注多Agent系统性能的同时,也关注各个Agent的收益。本文提出一种基于双向选择的多Agent系统集成方案,在此方案中,Agent根据自身的意愿选择合适的角色进行申请,同时角色根据对各个Agent的信任值选择合适的Agent来承担其任务。实验表明,随着若干次系统学习,多Agent系统协作任务完成时间能较快地下降,Agent在单位时间内的收益逐步提高。     

Supply chain coordination under budget constraints

Budget constraints are commonly considered in real decision frameworks; however, the literature has rarely addressed the design of contracts for supply chains with budget-constrained members and in which capital costs are considered. In this article, we study supply chain coordination of budget-constrained members when a financial market is unavailable. We propose a revenue-sharing-and-buy-back (RSBB) contract that combines revenue-sharing (RS) and buy-back (BB) contracts. We compare the performance of RS, BB, and RSBB contracts under a coordinated two-stage supply chain in which members experience budget constraints. Results show that the RS and BB contracts are not feasible under certain budget scenarios, whereas the RSBB contract can always be used to coordinate the supply chain and arbitrarily divide profits. We propose a profit allocation approach to address information symmetry created by undisclosed budget thresholds. Our analytical and numerical results provide insight into how managers select an appropriate contract based on their budget scenarios and capital costs.     

Enforceable component-based realtime contracts

We present enforceable component-based realtime contracts, the first extension of component-based software engineering technology that comprehensively supports adaptive realtime systems from specification all the way to the running system.To provide this support, we have extended component-based interface definition languages (IDLs) and component representations in repositories to express realtime requirements for components. The final software, which is assembled from the components, is then executed on a realtime operating system (RTOS) with the help of a component runtime system. RTOS resource managers and the IDL-extensions are based on the same mathematical foundation. Thus, the component runtime system can use information expressed in a component-oriented manner in the extended IDL to derive parameters for the task-based admission and scheduling in the RTOS. Once basic realtime properties can thus be guaranteed, runtime support can be extended to more elaborate schemes that also support adaptive applications (container-managed quality assurance).We claim that this study convincingly demonstrates how component-based software engineering can be extended to build systems with non-functional requirements.     

A reflective infrastructure for workflow adaptability

We present a flexible framework that enables workflow systems to adapt to changing conditions. The model is designed to reveal key aspects of the tasks involved in representing and enacting business processes. These fundamental characteristics are identified as state, behaviour, distribution, coordination and enactment. By isolating such core concepts in a way that allows them to be varied, we open up the general process of task coordination and execution, allowing for extensions in a planned way. By suitable manipulation of each of these aspects, at the appropriate level, a workflow system may be extensively modified in a way that minimises the effect of such change upon other aspects of the system.     

Sampling frequency and controllability region

In order to decide on the sampling frequency in a digital control system, a measure V is introduced for the subset of states, which can be transferred to the origin within a given time interval θ by a constrained control input. V increases with the number N of samplings in the interval θ = NT, but at the same time the required computer time increases. It is shown, how V(T) can be computed for multi-variable systems. A plot of V(T) allows a trade-off between controllability region and computer time by choice of the sampling interval T.     

State space measures of robustness of pole locations for structured and unstructured perturbations

Measures of pole location robustness for linear feedback systems are derived from a state space model of the system. The robustness tests ensure that the eigenvalues of the perturbed systems matrix A + E remain in a desired region D of the complex plane containing the eigenvalues of the nominal system matrix A. The region D may be any open set of the complex plane whatsoever. The results are expressed in terms of induced matrix norms and apply to structured perturbations of the form E = BΔC, where B and C define the structure of E, and may be nonsquare matrices. Rank one perturbations E of minimal norm and with the given structure that will cause A + E to have an eigenvalue outside of D are constructed for the cases when the matrix norm is induced by the vector 1-norm or the vector ∞-norm. The advantages of having robustness measures for several matrix norms that can be computed are illustrated with a simple example that demonstrates how the conservatism of single tests can be reduced using several tests (i.e. several matrix norms). A method for computing numerically the robustness measures for particular norms is presented. It can be used to compute, with a guaranteed degree of accuracy, the maximum of the norm of the frequency response of a system.     

Supply-chain coordination with combined contract for a short-life-cycle product

A contract is a mechanism to realize the performance improvement of a supply-chain system or to achieve the perfect coordination of a supply-chain channel. This paper deals with the coordination issue of a selling channel for a short-life-cycle product. First, a new type of contract combining the return policy with markdown money according to the practice under which some companies sell their products with different marketing policies in different selling periods is designed. This case is illustrated using a stochastic dynamic-programming model. Then, the necessary condition to achieve channel coordination with this combined contract is derived; and given the scheme to allocate the coordination profit, the generalized method to find the optimal contract parameters is developed. Lastly, with analysis and simulations, it can be concluded that the supply-chain coordination with the single contract in literatures for two-period selling depends on the demand distribution and the cost structure of a system, but the combined contract that was designed depends only on the cost structure of a system. It can further be concluded that the combined contract can ensure channel coordination and arbitrarily allocate coordination profit, and that the combined contract is generalized with several classical contracts as its special examples. Furthermore, the supplier will become the active initiator of the combined contract under the high-risk setting because the combined contract can strengthen his status in the channel system and improve his performance.     

Grounding Privacy in Mediated Communication

This paper addresses the need of interpersonal privacy coordination mechanisms in the context of mediated communication, emphasizing the dialectic and dynamic nature of privacy. We contribute the Privacy Grounding Model—built upon the Common Ground theory—that describes how connected individuals create and adapt privacy borders dynamically and in a collaborative process. We present the theoretical foundations of the model. We also show the applicability of the model, where we give evidence from a field study that illustrates how it can describe privacy coordination mechanisms amongst users of an instant messaging application and a desktop awareness system. The model describes efficient and effective factors that communicators consider in their decisions to use mechanisms for coordination. The Privacy Grounding Model aims to help designers reflect on how their system supports, or fails to support, people’s need for lightweight and distinctive privacy coordination mechanisms, and in particular how communicators within the system create and use privacy border representations for grounding their needs to interact with each other.     

Integration of FMS performance evaluation models using patterns for an information system design

The objective of our work is to create an information system able to integrate different view points concerning the design and the control of a Flexible Manufacturing System. Numerous methods based on generic reference frameworks have been proposed for the modeling of all the aspects of production systems. These models have to be instantiated in order to be applied to specific systems. The difficulties are then to integrate pre-existing models of the studied systems with those obtained by the instantiation of the generic reference framework.

The proposed approach tackles the problem from the information system point of view. A meta-modeling bottom-up approach is presented based on the notion of patterns in order to facilitate the integration step.

An example concerned with the performance evaluation and scheduling of a production system is presented to show how the product viewpoint can be built in order to be integrated later with other viewpoints.     

Contract-based modeling and verification of timed safety requirements within SysML

In order to cope with the growing complexity of critical real-time embedded systems, systems engineering has adopted a component-based design technique driven by requirements. Yet, such an approach raises several issues since it does not explicitly prescribe how system requirements can be decomposed on components nor how components contribute to the satisfaction of requirements. The envisioned solution is to design, with respect to each requirement and for each involved component, an abstract specification, tractable at each design step, that models how the component is concerned by the satisfaction of the requirement and that can be further refined toward a correct implementation. In this paper, we consider such specifications in the form of contracts. A contract for a component consists in a pair (assumption, guarantee) where the assumption models an abstract behavior of the component’s environment and the guarantee models an abstract behavior of the component given that the environment behaves according to the assumption. Therefore, contracts are a valuable asset for the correct design of systems, but also for mapping and tracing requirements to components, for tracing the evolution of requirements during design and, most importantly, for compositional verification of requirements. The aim of this paper is to introduce contract-based reasoning for the design of critical real-time systems made of reactive components modeled with UML and/or SysML. We propose an extension of UML and SysML languages with a syntax and semantics for contracts and the refinement relations that they must satisfy. The semantics of components and contracts is formalized by a variant of timed input/output automata on top of which we build a formal contract-based theory. We prove that the contract-based theory is sound and can be applied for a relatively large class of SysML system models. Finally, we show on a case study extracted from the automated transfer vehicle (http://www.esa.int/ATV) that our contract-based theory allows to verify requirement satisfaction for previously intractable models.     

Parallel-architecture-directed program transformation

The widespread use of parallel machines has been hampered by the difficulty of mapping applications onto them effectively. The difficulty arises because current programming languages require the programmer to specify a problem to be solved at a low level of abstraction in an imperative form. Thus the programmer must immediately encode an architecture-specific algorithm detailing every communication and calculation. This process is prone to error and complicates the reuse of software.

An alternative approach is to specify the problem to be solved at a high-level in a functional language. Meaning-preserving program transformations can then be used to derive a parallel algorithm. Such algorithms can be run on parallel graph-reduction or dataflow machines which automatically exploit the implicit parallelism in a functional language program. Such automatic decomposition techniques, however, are not yet capable of fully yielding the extra performance offered by the parallel hardware.

We show how, by including an architecture specification with the problem specification, and extending the amount of transformation performed, it is possible to produce functional language code that explicity expresses the calculations and communications to be performed by the processors. This simplifies compilation, yields faster programs and enables parallel software to be developed for a wide variety of parallel computer architectures.

A goal-seeking transformation methodology has been developed which enables a high-level functional specification of the problem and a high-level functional abstraction of the target computer architecture to be systematically manipulated to produce an efficient parallel algorithm tailored to the target architecture. As the transformations start from very high-level specifications, the discovery of new algorithms is facilitated.

A case study is used to demonstrate the effectiveness of the technique. We show how a high level specification for sort can be transformed with a pipeline architecture specification to give a mergesort and how the same specification with a dynamic-message-passing architecture specification can be transformed to a novel parallel quicksort.     

Token-ordered LRU: an effective page replacement policy and its implementation in Linux systems

Most computer systems use a global page replacement policy based on the LRU principle to approximately select a Least Recently Used page for a replacement in the entire user memory space. During execution interactions, a memory page can be marked as LRU even when its program is conducting page faults. We define the LRU pages under such a condition as false LRU pages because these LRU pages are not produced by program memory reference delays, which is inconsistent with the LRU principle. False LRU pages can significantly increase page faults, even cause system thrashing. This poses a more serious risk in a large parallel systems with distributed memories because of the existence of coordination among processes running on individual node. In the case, the process thrashing in a single node or a small number of nodes could severely affect other nodes running coordinating processes, even crash the whole system. In this paper, we focus on how to improve the page replacement algorithm running on one node.

After a careful study on characterizing the memory usage and the thrashing behaviors in the multi-programming system using LRU replacement. we propose an LRU replacement alternative, called token-ordered LRU, to eliminate or reduce the unnecessary page faults by effectively ordering and scheduling memory space allocations. Compared with traditional thrashing protection mechanisms such as load control, our policy allows more processes to keep running to support synchronous distributed process computing. We have implemented the token-ordered LRU algorithm in a Linux kernel to show its effectiveness.