Quality-constrained routing in publish/subscribe systems

Routing in publish/subscribe (pub/sub) features a communication model where messages are not given explicit destination addresses, but destinations are determined by matching the subscription declared by subscribers. For a dynamic computing environment with applications that have quality demands, this is not sufficient. Routing decision should, in such environments, not only depend on the subscription predicate, but should also take the quality-constraints of applications and characteristics of network paths into account. We identified three abstraction levels of these quality constraints: functional, middleware and network. The main contribution of the paper is the concept of the integration of these constraints into the pub/sub routing. This is done by extending the syntax of pub/sub system and applying four generic, proposed by us, guidelines. The added values of quality-constrained routing concept are: message delivery satisfying quality demands of applications, improvement of system scalability and more optimise use of the network resources. We discuss the use case that shows the practical value of our concept

A Massively Scalable Architecture For Instant Messaging & Presence

This paper analyzes the scalability of Instant Messaging & Presence (IM&P) architectures. We take a queueing-based modelling and analysis approach to find the bottlenecks of the current IM&P architecture at the Dutch social network Hyves, as well as of alternative architectures. We use the Hierarchical Evaluation Tool (HIT) to create and analyse models analytically. Based on these results, we recommend a new architecture that provides better scalability than the current one. \u

Transparent Dynamic reconfiguration for CORBA

Distributed systems with high availability requirements have to support some form of dynamic reconfiguration. This means that they must provide the ability to be maintained or upgraded without being taken off-line. Building a distributed system that allows dynamic reconfiguration is very intrusive to the overall design of the system, and generally requires special skills from both the client and server side application developers. There is an opportunity to provide support for dynamic reconfiguration at the object middleware level of distributed systems, and create a dynamic reconfiguration transparency to application developers. We propose a Dynamic Reconfiguration Service for CORBA that allows the reconfiguration of a running system with maximum transparency for both client and server side developers. We describe the architecture, a prototype implementation, and some preliminary test result

Platform-independent Dynamic Reconfiguration of Distributed Applications

The aim of dynamic reconfiguration is to allow a system to evolve incrementally from one configuration to another at run-time, without restarting it or taking it offline. In recent years, support for transparent dynamic reconfiguration has been added to middleware platforms, shifting the complexity required to enable dynamic reconfiguration to the supporting infrastructure. These approaches to dynamic reconfiguration are mostly platform-specific and depend on particular implementation approaches suitable for particular platforms. In this paper, we propose an approach to dynamic reconfiguration of distributed applications that is suitable for application implemented on top of different platforms. This approach supports a platform-independent view of an application that profits from reconfiguration transparency. In this view, requirements on the ability to reconfigure components are expressed in an abstract manner. These requirements are then satisfied by platform-specific realizations

Reconfiguration Service for Publish/Subscribe Middleware

Mission-critical, distributed systems are often designed as a set of distributed, components that interact using publish/subscribe middleware. Currently, in these systems, software components are usually statically allocated to the nodes to fulfil predictability, reliability requirements. However, a static allocation of components has major drawbacks, e.g. the need for quantification of the expenditure of resources to prevent a lack of resources during runtime. A dynamic allocation diminishes the drawbacks of a static allocation by reallocating components during system run-time. The process of dynamic reallocation is considered as a reconfiguration of the system, which can be implemented as an additional functionality of the middleware. In this paper, we propose a new dynamic reconfiguration service for a publish/subscribe middleware that enables dynamic reallocation of components in order to achieve predictable and reliable system behaviour and fulfil deployment requirements. We have built a prototype that validates our research

Trustworthy applications for vehicular environments

The integration of ICT in vehicular environments enables new kinds of application and creates new technological challenges. Dynamic network topology, unreliable network links, and moving terminals make it hard to provide a convincing end user experience. This article introduces the concept of providing trustworthy applications through wireless networks in vehicular environments. A special emphasis will be on how to maintain end users privacy when providing personalized, contextaware services. Therefore, a service taxonomy, enabling middleware technologies, and service enablers are introduced

Dynamic reconfiguration for middleware-based applications

Distributed systems with high availability requirements have to allow reconfiguration of the system without being taken off-line. Examples of reconfigurations are the replacement of a component with a newer version, or the migration of a component to another node. A key issue for reconfiguration is maintaining the correctness of the system, which can be very complex due to the number of components, unclear relations between components, heterogeneity in operating systems and programming languages, and physical distribution of components. In this paper, we describe a new approach for dynamic reconfiguration of middleware-based applications that is more transparent for the application developer than existing approaches. We compare our approach with other approaches, and describe a prototype that implements our approach for CORBA-based applications

The Prospective Dutch Colorectal Cancer (PLCRC) cohort: real-world data facilitating research and clinical care

Real-world data (RWD) sources are important to advance clinical oncology research and evaluate treatments in daily practice. Since 2013, the Prospective Dutch Colorectal Cancer (PLCRC) cohort, linked to the Netherlands Cancer Registry, serves as an infrastructure for scientific research collecting additional patient-reported outcomes (PRO) and biospecimens. Here we report on cohort developments and investigate to what extent PLCRC reflects the “real-world”. Clinical and demographic characteristics of PLCRC participants were compared with the general Dutch CRC population (n = 74,692, Dutch-ref). To study representativeness, standardized differences between PLCRC and Dutch-ref were calculated, and logistic regression models were evaluated on their ability to distinguish cohort participants from the Dutch-ref (AU-ROC 0.5 = preferred, implying participation independent of patient characteristics). Stratified analyses by stage and time-period (2013–2016 and 2017–Aug 2019) were performed to study the evolution towards RWD. In August 2019, 5744 patients were enrolled. Enrollment increased steeply, from 129 participants (1 hospital) in 2013 to 2136 (50 of 75 Dutch hospitals) in 2018. Low AU-ROC (0.65, 95% CI: 0.64–0.65) indicates limited ability to distinguish cohort participants from the Dutch-ref. Characteristics that remained imbalanced in the period 2017–Aug’19 compared with the Dutch-ref were age (65.0 years in PLCRC, 69.3 in the Dutch-ref) and tumor stage (40% stage-III in PLCRC, 30% in the Dutch-ref). PLCRC approaches to represent the Dutch CRC population and will ultimately meet the current demand for high-quality RWD. Efforts are ongoing to improve multidisciplinary recruitment which will further enhance PLCRC’s representativeness and its contribution to a learning healthcare system

Dynamic reconfiguration and load distribution in component middleware

The ability to control the Quality of Service (QoS) characteristics of\ud distributed systems is essential for their success. The QoS characteristics that we consider in this thesis are performance characteristics (response time and throughput) and availability characteristics (uptime, mean-timebetween-disruptions and mean-time-to-repair). The research presented in this thesis can be used to develop commercial QoS mechanisms that improve the QoS of component-middleware-based applications