Synthesis of Reo circuits from scenario-based interaction specifications

It is difficult to construct correct models for distributed large-scale service-oriented applications. Typically, the behavior of such an application emerges from the interaction and collaboration of multiple components/services. On the other hand, each component, in general, takes part in multiple scenarios. Consequently, not only components, but also their interaction protocols are important in the development process for distributed systems. Coordination models and languages, like Reo, offer powerful “glue-code” to encode interaction protocols. In this paper we propose a novel synthesis technique, which can be used to generate Reo circuits directly from scenario specifications. Inspired by the way UML2.0 sequence diagrams can be algebraically composed, we define an algebraic framework for merging connectors generated from partial specifications by exploiting the algebraic structure of UML sequence diagrams.     

Weighted residual methods and the suboptimal control of distributed parameter systems†

A suboptimal control algorithm for distributed parameter systems is developed in a framework which synthesizes weighted residual methods and mathematical programming. The heat exchanger example of Koppel et al. (1968) is employed for introducing the algorithm. First, the Galerkin procedure with polynomial modes is applied to obtain a lumped ODE model for the distributed parameter system. Then the state and control variables of the lumped control problem are approximated by cubic splines on a uniform mesh. Through collocation at the knots, the ODE model is reduced to a sot of linear algebraic equations and the suboptimal control is determined from the solution of a quadratic programming problem with sparse matrices.

Numerical results for the heat exchanger example are presented and compared with those obtained by the authors (Neuman and Sen 1972) using the Ritz-Trefftz algorithm (Bosarge and Johnson 1970) for the lumped control problem. For this example, the two algorithms yield essentially identical results with comparable computational requirements. Application of the Ritz-Trefftz algorithm, however, is limited to lumped, linear-quadratic control problems without constraints on the state or control. The approach advocated in this paper, therefore, offers a viable approach to control problems in distributed parameter systems.     

MALC的公式在其模型间互模拟下的不变性

文献[1]中给出了模态描述逻辑的语法与语义,同时给出了两个模型之间的互模拟关系。目前对各种模态描述逻辑系统的研究主要是它们的语法与语义,对其代数性质做研究很少见,然而研究各种模态描述逻辑系统的模型构造,模型之间互模拟、同构等代数性质有重要的理论与现实意义。文中在文献[1]的基础上,定义了模态描述逻辑的可能世界的理论和两个可能世界的等价,继续研究描述逻辑系统的代数性质,得到了的合式公式在模型间互模拟下的不变性。     

Abstract abstract reduction

We propose novel algebraic proof techniques for rewrite systems. Church–Rosser theorems and further fundamental statements that do not mention termination are proved in Kleene algebra. Certain reduction and transformation theorems for termination that depend on abstract commutation, cooperation or simulation properties are proved in an extension with infinite iteration. Benefits of the algebraic approach are simple concise calculational proofs by equational reasoning, connection with automata-based decision procedures and a natural formal semantics for rewriting diagrams. It is therefore especially suited for mechanization and automation.     

Coordination Models Based on a Formal Model of Distributed Object Reflection

We propose a family of models of coordination of distributed object systems representing different views, with refinement relations between the different views. We start with distributed objects interacting via asynchronous message passing. The semantics of such a system is a set of event partial orders (event diagrams) giving the interactions during possible system executions. A global coordination requirement is a constraint on the allowed event diagrams. A system coordination specification consists of a meta-level coordinator that controls message delivery in the system according to a given global policy. The system-wide coordination can be refined/distributed using coordinators for disjoint subsystems that communicate with their peers to enforce the global policy. By a further transformation the meta-level can be replaced by systematically transformed base-level objects communicating via a controller object. The coordination models are formalized in rewriting logic using the Reflective Russian Dolls model of distributed object reflection. The general ideas are illustrated with several examples.     

Filtering in nonlinear time delay systems

Linear and nonlinear (extended Kalman-Bucy) filters are derived for systems governed by coupled partial and integro-differential equations. The framework used is sufficiently general that filters for 1) lumped parameter systems having multiple time varying or constant time delays, 2) coupled lumped and hyperbolic distributed parameter systems, and 3) lumped parameter systems with functional time delays, evolve as special cases. Although the filtering equations are the final result, the corresponding smoothing equations are developed as well. The performance of the filter is illustrated through application to a well stirred chemical reactor with external heat exchange.     

Observability conditions for a class of mixed distributed and lumped parameter systems

Observability of a class of mixed distributed and lumped parameter systems with respect to physically realizable measurements is studied. Measurements are made either on the lumped subsystem or at interior points of the spatial domain. In both cases algebraic observability conditions are determined and the results applied to a transportation lag system.     

Lumped parameter estimation for the embryonic chick vascular system: a time-domain approach using MLAB

We have evaluated several lumped parameter analog models for the early chick embryonic vascular system that may be used to infer loading characteristics of the developing heart. We measured dorsal aortic pressure and flow simultaneously with a servo-null pressure system and a pulsed Doppler velocimeter. Four different analog circuit models were chosen for comparisons. We formulated the time-domain differential equations specifying the relations between pressure and flow in the models, and then estimated the lumped parameters that produced the best fit. The MLAB mathematical modeling software was used for solving differential equations, and for minimizing the difference between model-predicted values and experimental data. The traditional three-element Windkessel model with an added inductance term was most often the best-fitting model. This is compatible with the previous study using a frequency-domain approach. The procedures developed for the current study are adaptable for the study of a variety of nonlinear models, and distributed parameter models for mammalian cardiovascular development with mechanically, pharmacologically, or genetically altered conditions.     

On families of systems and deformations

Parameter variations are present in most physical systems. In some cases, such variations can be safely ignored, and one might, for instance, design control loops for some average parameter values. However, in many interesting cases, the variations have to be taken into account in order to design good, or even adequate, control algorithms. Furthermore, the concerns of system reliability demand predictions of possible consequences of large deviations in parameters. Although some of the work in adaptive control is in this spirit, until recently there has.not been any systematic effort towards a theory of systems with parameter variations. We argue here that the concept of families of systems is basic to such an effort. Whereas the necessary tools for the study of individual linear systems with fixed parameters are contained in the theory of differential equations and linear algebra, the techniques of Lie theory, differential geometry and algebraic geometry play an essential role in the study of families of systems. The core of this paper is concerned with the geometric characterizations of certain families of systems that appear in control and identification problems. We also isolate some of the ways in which families of systems degenerate as parameter variations become large. For the purposes of exposition, we work mostly with the so-called ‘ topological case ’ (over R) as opposed to the algebraic geometric case (over C).     

Variational embedding method and application to distributed systems control

The main aim of the present paper is to show the variational embedding method as a powerful tool for solving control problems associated with distributed systems. It is shown that, variational embedding subsumes many approximation methods that are available in the literature for solving constitutive equations of distributed systems. The well-known method of weighted residuals and its ramifications are shown to be the appropriate specializations of the embedding method. The method thus offers a vantage point from which it is conceptually easy to see both the plurality and unity of these methods. In the process of illustrating the hierarchy of the method, the attendant dilemma associated with the method of weighted residuals is successfully resolved. The variational embedding method yields a unified approach for obtaining lumped models for distributed parameter systems. The application is demonstrated by considering examples of engineering importance, and it is shown how lumped models of non-linear distributed systems could be constructed by methods other than the conventional discretization methods.     

Quantitative and qualitative analysis of SysML activity diagrams

Model-driven engineering refers to a range of approaches that uses models throughout systems and software development life cycle. Towards sustaining such a successful approach in practice, we present a model-based verification framework that supports the quantitative and qualitative analysis of SysML activity diagrams. To this end, we propose an algorithm that maps SysML activity diagrams into Markov decision processes expressed using the language of the probabilistic symbolic model checker PRISM. Furthermore, we elaborate on the correctness of our translation algorithm by proving its soundness with respect to a SysML activity diagrams operational semantics that we also present in this work. The generated models can be verified against a set of properties expressed in the probabilistic computation tree logic. To automate our approach, we developed a prototype tool that interfaces a modeling environment and the probabilistic model checker. We also show how to leverage adversary generation to provide the developer with a useful counterexample/witness as a feedback on the verified properties. Finally, the established theoretical foundations are complemented with an illustrative case study that demonstrates the usability and benefit of such a framework.     

模态描述逻辑MALC模型的几个代数性质

本文定义了MALC模型间的同构、同态等关系,并讨论了合式公式在这些关系下的不变性等代数性质。最后定义了MALC的拓扑语义及基于拓扑语义互模拟,得到MALC的合式公式在拓扑互模拟下具有不变性。     

Feedback control of linear systems with distributed delay

The problem of optimal control of linear systems containing lumped delay, given by differential-difference equations, has been pursued by several authors. However, transportation-lags are better described by distributed delays giving systems that are described by a set of coupled partial and ordinary differential equations. The lumped part of the system is described by ordinary differential equations and the distributed part of the system is described by partial differential equations. The lumped as well as distributed parts are subject to control. The present paper discusses the control of such systems with quadratic performance measures. Riccati-like equations are derived and a technique for their numerical solution is presented.     

A formal verification framework for SysML activity diagrams

SysML activity diagrams are OMG/INCOSE standard diagrams used for modeling and specifying probabilistic systems. They support systems composition by call behavior and send/receive artifacts. For verification, the existing approaches dedicated to these diagrams are limited to a restricted set of artifacts. In this paper, we propose a formal verification framework for these diagrams that supports the most important artifacts. It is based on mapping a composition of SysML activity diagrams to the input language of the probabilistic symbolic model checker called “PRISM”. To prove the soundness of our mapping approach, we capture the underlying semantics of both the SysML activity diagrams and their generated PRISM code. We found that the probabilistic equivalence relation between both semantics preserve the satisfaction of the system requirements. Finally, we demonstrate the effectiveness of our approach by presenting real case studies.     

Control of technological and production processes as distributed parameter systems based on advanced numerical modeling

The paper describes some practical control problems of technological and production processes as nonlinear distributed parameter systems. These are solved based on advanced numerical modeling in virtual software environments offered for the numerical dynamic analysis of technological and production processes with co-simulations. The controlled systems are interpreted as nonlinear lumped input and distributed parameter output systems. Synthesis of control in space relation is solved by approximation methods in temporal relation by methods of control of lumped parameter systems. Some results are demonstrated by the control of the secondary cooling in the continuous casting of steel, based on a software sensor. Furthermore, the control of a casting die preheating process is introduced in this framework using a programmable logic controller (PLC).     

Stability analysis of a class of non-linear distributed parameter systems—tubular chemical reactors†

A sufficient condition for local stability of the spatially discretized model of a class of non-linear distributed parameter systems is derived using the circle criterion for stability and bounded-input, bounded-output stability. As a physical system the catalytic packed-bed tubular reactor is taken to illustrate the application of the theorem to process control systems. The stability condition in the large derived from non-linear system equations is compared with the stability condition in the small derived from linearized system equations. Interpretations of the result are given in terms of physical variables.     

Formal modeling and validation of Stateflow diagrams

Stateflow is an industrial tool for modeling and simulating control systems in model-based development. In this paper, we present our latest work on automatic verification of Stateflow using model-checking techniques. We propose an approach to systematically translate Stateflow diagrams to a formal modeling language called CSP# by precisely following Stateflow’s execution semantics, which is described by examples. A translator is developed inside the Process Analysis Toolkit (PAT) model checker to automate this process with the support of various Stateflow advanced modeling features. Formal analysis can be conducted on the transformed CSP# with PAT’s simulation and model-checking power. Using our approach, we can not only detect bugs in Stateflow diagrams, but also discover subtle semantics flaws in Stateflow user’s guide and demo cases.     

Toward the Next Generation of Data Modeling Tools

This paper describes the Update Protocol Model (UPM), a formal language for the expression of database update semantics. UPM has been used primarily to capture and communicate in a precise and uniform notation the plethora of database semantics described by a variety of "fourth generation" models, many of which are imprecise when it comes to update semantics. Several computing trends–knowledge-based expert systems, distributed database management systems, and new applications based on higher order semantic models–point to the need for modeling techniques beyond that which current data models such as the relational and entity-relationship models provide.