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Object-Oriented Real-Time Dependable Systems, 2001. Proceedings. Sixth International Workshop on

Date 8-10 Jan. 2001

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  • Proceedings Sixth International Workshop on Object-Oriented Real-Time Dependable Systems

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    Freely Available from IEEE
  • Author index

    Page(s): 269
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    Freely Available from IEEE
  • Time vs. space in fault-tolerant distributed systems

    Page(s): 21 - 27
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (496 KB) |  | HTML iconHTML  

    Algorithms for solving agreement problems can be classified in two categories: (1) those relying on failure detectors (FDs), which we call FD-based, and (2) those that rely on a group membership service (GMS), which we call GMS-based. This paper discusses the advantages and limitations of these two approaches and proposes an extension to the GMS approach that combines the advantages of both approaches, without their drawbacks. This extension leads us to distinguish between time-triggered suspicions of processes and space-triggered exclusions View full abstract»

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  • Open multithreaded transactions: keeping threads and exceptions under control

    Page(s): 197 - 205
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    Although transactional models have proved to be very useful for numerous applications, the development of new models to reflect the ever-increasing complexity and diversity of modern applications is a very active area of research. Analysis of the existing models of multithreaded transactions shows that they either give too much freedom to threads and do not control their participation in transactions, or unnecessarily restrict the computational model by assuming that only one thread can enter a transaction. Another important issue, which many models do not address properly, is providing adequate exception handling features. A new model of multithreaded transactions is proposed. Its detailed description is given, including rules of thread behaviour when transactions start, commit and abort, and rules of exception raising, propagation and handling. This model is supported by enhanced error detection techniques to allow for earlier error detection and for localised recovery. General approaches to implementing transaction support are discussed and a detailed description of an Ada implementation is given. Special attention is paid to outlining typical applications for which this model is suitable and to comparing it with several known approaches (Coordinated Atomic actions, CORBA, and Argus) View full abstract»

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  • Component-based software engineering for resource-constraint systems: what are the needs?

    Page(s): 91 - 94
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (432 KB) |  | HTML iconHTML  

    The article summarizes the most important problems that must be solved in order to establish a component-based software engineering (CBSE) discipline for resource-constraint systems. Resource-constraints are especially relevant for embedded systems (e.g. telecommunication systems and many modern consumer products), real-time systems and dependable safety-critical systems, but can be encountered in virtually all types of systems. The authors define a number of research challenges in the form of requirements that are not yet met by contemporary component models. For each requirement, we explain its relevance and suggest directions for possible solutions. We concentrate on the architectural level, since it is here that CBSE has the highest benefits in terms of adaptability arid reuse. We also do not consider non functional constraints in general, but only dependability constraints (timeliness, performances, reliability, availability and security). The reason is that the latter directly affect the feasibility of a given component configuration, while this is less obvious for general constraints like scalability, maintainability and interoperability View full abstract»

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  • Client-side enhancements using portable interceptors

    Page(s): 179 - 185
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (584 KB) |  | HTML iconHTML  

    Interceptors are a useful technique for extending the basic functionality provided by an Object Request Broker without changing its implementation, nor affecting client code. The recently proposed CORBA standard includes a new definition of portable interceptors. This definition is very powerful, yet not trivial to use. The authors review this definition, and discuss how it can be applied to provide client side enhancement for caching, load-balancing, flow control (quality of service), and fault-tolerant soft real-time. A recommendation to the OMG for a very minor change in the standard that could greatly simplify its usability is also provided View full abstract»

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  • Super actors for real time

    Page(s): 142 - 149
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (568 KB) |  | HTML iconHTML  

    The paper proposes a novel approach, SART, to the development of real-time systems which is based on super actors, i.e., actors whose behaviour is modelled by statecharts. SART borrows structural concepts from known methods for reactive systems like ROOM and UML-RT, and favours ease of construction by making actors reusable and composable software components. The distinguishing factors of SART are its modularisation of timing constraints and customisable scheduling algorithm. Application actors are not aware of timing requirements. RTsynchronizers capture timing constraints in groups of actors, filter relevant messages and control their scheduling. Time clauses of causally connected messages in system interactions are directly derived from the declarative specification of end-to-end timing constraints. SART supports both prototyping and real-time execution modes. A SART graphical development environment supporting modelling, temporal property checking and code generation has been implemented in Java View full abstract»

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  • A middleware implementation and performance evaluation of the SNS scheme for network surveillance

    Page(s): 43 - 50
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (612 KB) |  | HTML iconHTML  

    Network surveillance (NS), which is basically a (partially or fully) decentralized mode of detecting the faulty/repaired status of distributed computing (DC) components, is a major part of real-time (RT) fault-tolerant DC. One NS technique which is broadly applicable and amenable to rigorous quantitative analyses of fault coverage is the supervisor-based network surveillance (SNS) scheme for use in point-to-point network-based systems. Recently, we have been studying an approach to implementing the SNS scheme within a middleware model, named the TMO (time-triggered message-triggered object) Support Middleware (TMOSM) which is layered above a commercial off-the-shelf (COTS) operating system such as Windows 2000 and functions as a reliable RT execution engine for RT DC applications. The DC applications supported by the TMOSM are those designed by use of the TMO programming scheme. The implementation structure as well as the observed performance of a prototype implementation are discussed View full abstract»

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  • Using semantic knowledge of distributed objects to increase reliability and availability

    Page(s): 153 - 160
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (636 KB) |  | HTML iconHTML  

    As systems become more distributed, they also become more complex. To ensure consistent execution while maximizing availability, distributed applications use various mechanisms such as replication, load balancing, and data caching. The protocols used for consistency management and component availability are traditionally instantiated by the application. However, in distributed object based environments like CORBA or Java RMI, the infrastructure can often determine adequate protocols to guarantee liveness and safety based on the request and semantic knowledge of the application. This paper discusses how semantic knowledge of distributed objects can help implement intelligent behavior in middleware and choose optimal protocols for distributed component interactions View full abstract»

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  • Framework for component-based development of distributed real-time systems

    Page(s): 85 - 90
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (564 KB) |  | HTML iconHTML  

    Modeling and design of distributed real-time embedded systems tend to be a very complex work, especially when heterogeneous systems and task synchronization are involved. In this sense, a specific framework can help in dealing with such complexity. The paper describes such a framework, which has been developed to help developers in the task of modeling and implementation of embedded real-time applications. The framework extends SIMOO-RT an object oriented software tool developed at UFRGS, with the possibility of using components. A component library template, the use of a deployment diagram for the configuration of a given component based solution to different target architectures, and a new code generator are the main extensions proposed. The paper gives an overview on the proposed extensions, explaining its use by means of some developed case studies View full abstract»

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  • Modeling and analysis of the behavior of GPRS systems

    Page(s): 51 - 58
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (560 KB) |  | HTML iconHTML  

    The General Packet Radio Service (GPRS) has recently become a standard to extend the services provided by the Global System for Mobile Communications (GSM). GPRS addresses packet-oriented traffic, by allowing a more efficient usage of the radio resources with a consequent improvement in the quality of service (QoS) for subscribers. This paper focuses on a preliminary evaluation of dependability and performance figures of the GPRS, by analyzing its behavior during the contention phase where users compete for the channel reservation. The presented work constitutes the first step towards the analysis of the GPRS under critical conditions, as determined by periods of outages, which significantly impact on the dependability, of the GPRS itself. In fact, outages imply service unavailability, with a consequent accumulation of users actively waiting for making a service request, leading to a higher probability of collisions on requests (and therefore a degradation of the QoS perceived by the users) when the system comes back up again. In this paper, some analyses have been performed using a simulation approach, to gain insights on appropriate settings for the GPRS, at varying values of internal and external system conditions View full abstract»

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  • The emerging real-time standard [UML]

    Page(s): 3 - 9
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    We describe the objectives, rationale and content of the newly proposed real-time Unified Modeling Language (UML) profile standard for the Object Management Group (OMG). The intent of this profile is to enable the inclusion of quantitative temporal information into UML models so that they can be analyzed for key time-related properties such as schedulability and performance. The primary purpose of the paper is to solicit feedback from real-time domain experts prior to formal adoption of the standard View full abstract»

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  • Building dependable software for critical applications: multi-version software versus one good version

    Page(s): 103 - 110
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (680 KB) |  | HTML iconHTML  

    An increasing range of industries have a growing dependence on software based systems, many of which are safety-critical, real-time applications that require extremely high dependability. Multi-version programming has been proposed as a method for increasing the overall dependability of such systems. We describe an experiment to establish whether or not the multi-version method can offer increased dependability over the traditional single-version development approach when given the same level of resources. Three programs were developed independently to control a real-time, safety-critical system, and were put together to form a decentralized multi-version system. Three functionally equivalent single-version systems. were also implemented, each using the same amount of development resources as the combined resources of the multi-version system. The analytic results from this experiment show that 1) a single-version system is much more dependable than any individual version of the multi-version system, and 2) despite the poor quality of individual versions, the multi-version method still results in a safer system than the single-version solution. It is evident that regarding the single-version method as a "seem-to-be" safer design decision for critical applications is not generally justifiable. We conclude by describing plans for a follow up study based on our initial findings View full abstract»

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  • An implementation of electronic shopping cart on the Web system using component-object technology

    Page(s): 77 - 84
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (552 KB) |  | HTML iconHTML  

    Proposes a new mechanism for implementing an electronic shopping cart system system on the World Wide Web. The shopping cart system is a typical client-server system, and it includes the essential tasks to be implemented in a typical Web-based client-server system. The most important task is to maintain context data between successive user sessions. Although several methods which can be applied to implement the shopping cart system on the Web system have been proposed, none of them can attain the task of maintaining context data sufficiently. In this paper, we analyze the task and point out the following difficulties: (1) reliability, (2) safety and (3) session management. We then propose a new mechanism, called the context data storage (CDS) mechanism, to solve all of the above difficulties. In the proposed CDS mechanism, the context data for the session management is stored in the main memory of the client computer. As a result, the CDS mechanism can achieve both high reliability and high safety, as well as the capability of managing tuser sessions. Next, we use component object technology to implement the CDS mechanism. Then, we compare the performance of the shopping cart system using the proposed CDS mechanism with one using the previous methods. The results show that our proposed mechanism has solved all of the above difficulties (1), (2) and (3) and has attained efficient communications between clients and Web servers View full abstract»

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  • Multimedia presentation: generic and implementation model

    Page(s): 227 - 232
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB) |  | HTML iconHTML  

    A multimedia presentation is a synchronized, sequential or concurrent, and possibly interactive, delivery of streams of multimedia data such as video, audio, text and still images using audio-video output devices. The first step in realizing a multimedia presentation is to find a position for each media object in space and in time. Resolving space and time positions and switch conditions lead to the implementation diagram, in which a formal description of the implementation of the multimedia presentation is given. The spatio-temporal object-oriented data model for multimedia data is proposed. This model is given as the UML class diagram View full abstract»

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  • Strong replica consistency for fault-tolerant CORBA applications

    Page(s): 10 - 17
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    The Eternal system provides transparent fault tolerance for CORBA applications, without requiring modifications to the application or to the object request broker (ORB), and without requiring special skills of the CORBA application programmers. Eternal maintains strong replica consistency as replicas of objects perform operations, and even as they fail and are recovered. Eternal implements the new fault-tolerant CORBA standard View full abstract»

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  • The use of automata in modelling and building a real-time component based system

    Page(s): 69 - 76
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (764 KB) |  | HTML iconHTML  

    Stochastically enhanced timed automata are used to model components of real-time systems. These automata components can be combined and replaced as required, but only with other automata. A new technique is presented which allows an automaton to be mapped on to a JavaBean, which can then be combined with other JavaBeans and components using known techniques. A system known as STINGRAE (Swimming Training INteractive Goggles for Real-time Aquatic Environments) is used as an example of this technique View full abstract»

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  • Fault management in ECLIPSE

    Page(s): 28 - 33
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    ECLIPSE is a next-generation virtual telecommunication network that provides multimedia services that integrate voice, video, text and images. ECLIPSE facilitates the modular decomposition of new telecommunication services. In this paper, we sketch the challenges we face in making ECLIPSE highly available when running on top of a heterogenous and widely distributed system. We describe how we approach these challenges using the modular decomposition of services provided by ECLIPSE, together with its novel failure detection and recovery strategies View full abstract»

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  • A generic visualization framework to help debug mobile-object-based distributed programs running on large networks

    Page(s): 240 - 247
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (736 KB) |  | HTML iconHTML  

    A generic visualization framework (VF) is proposed in this paper with the aim of aiding the debugging of mobile object-based distributed programs running on large networks. This framework consists of three logical layers, namely, the lower public Intranet (PI), the middle visualization data structures (VDS), and the upper visualization user interface (VUI). The VDS makes the VF generic because data structures can be adapted easily to accommodate different platforms that support mobile objects (agents). The adaptation does not affect the VUI and PI features described in this paper. In the simulation and tests, the VF was adapted for the stable Aglets mobile agent platform, and the preliminary results confirm that the VF is indeed a viable approach to help debug mobile object-based distributed programs running on large networks such as the Internet View full abstract»

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  • Real-time based strong consistency for distributed objects

    Page(s): 161 - 168
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    A distributed computation satisfies sequential consistency if it is possible to establish a legal ordering of all the operations such that the program order of each site in the distributed system is respected. However, sequential consistency does not necessarily consider the particular real-time instant at which each operation is executed. A timed consistency model addresses how quickly the effects of an operation are perceived by the rest of the system, by requiring that if a write operation is executed at time t, it must be visible to the entire distributed system by time t+Δ.Timed consistency generalizes several existing consistency criteria and it is well suited for applications where the action of one user must be seen by others in a timely fashion View full abstract»

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  • Towards universal software substrate for distributed embedded systems

    Page(s): 206 - 213
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    The paper proposes a universal software substrate for building various types of distributed embedded systems. The universal software substrate contains an operating system and several middleware components. It offers a universal application programming interface (Universal API) that greatly increases an embedded application's portability. Also, it makes the development speed of distributed embedded applications dramatically fast, since the high level abstraction provided by universal software substrate decreases the amount of software that should be written from scratch. The most important issue of our research is how to control the level of abstraction when designing distributed embedded systems. Our work is looking for methodologies to build portable software for distributed embedded systems in a systematic way. We describe several software components towards realizing universal software substrate, and some research topics for achieving the goals View full abstract»

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  • Dealing with tasking overload in object oriented real-time applications design

    Page(s): 214 - 220
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (620 KB) |  | HTML iconHTML  

    This paper deals with the overload caused by excessive service requests from the environment for dynamic control systems. A method of providing gracefully degraded solutions is proposed, based on the previous work on the project dealing with the design of a consistent embedded real-time control system with the goal of increasing its dependability. A syntax is defined as an enhancement of the object oriented extension of a standard real-time programming language. Further, the task program execution times are estimated for possible execution paths, providing the necessary basis for schedulability analysis in both normal and critical operation modes View full abstract»

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  • Automatic implementation of real-time object-oriented models and schedulability issues

    Page(s): 137 - 141
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB) |  | HTML iconHTML  

    The object oriented design methods and their CASE tools are widely used in practice by many real time software developers. However, object oriented CASE tools require an additional step of identifying tasks from a given design model. Task identification is usually performed in an ad-hoc manner using hints provided by human designers. The authors present ongoing research into schedulability-aware, automatic synthesis of multi-threaded implementation of a real time object oriented design. We present several feasible implementation strategies and architectures. We propose our approach to automatic implementation and address schedulability issues involved in our approach View full abstract»

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  • Measuring the cost of scalability and reliability for Internet-based, server-centered applications

    Page(s): 59 - 66
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    With large numbers of geographically dispersed clients, a centralized approach to Internet-based application development is not scalable and also not dependable. This paper presents a decentralized approach to dependable Internet-based application development, consisting of a logical structuring of collaborating sub-systems of geographically separated replicated servers. Two implementations of an Internet auction, one using a centralized approach and the other using our decentralized approach, are described. To evaluate the scalability of the two approaches, a number of experiments are performed on these implementations and the results are presented View full abstract»

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  • Architectural Significant Package (ASP): fundamentals of object-oriented architecture modeling for real-time embedded applications

    Page(s): 129 - 136
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    Architecture modeling for real-time embedded applications presents a challenging issue in object oriented software development. The paper discusses the architectural modeling concepts and practices through an example of a real-time embedded project. During the project, a practical concept: the Architectural Significant Package (ASP) has been developed. Various ASPS are identified and integrated to form an architectural foundation for the project. In addition to the fundamental issues on identifying an ASP, the paper explores how to integrate ASPS into a cohesive and reusable model. Some interesting observations on this engineering practice of using the ASP approach will help to improve future architecture modeling in the real-time embedded environment View full abstract»

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