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This article elaborates the benefits of wireless technology to a process control system. In essence, wireless technology is about data transmissions, and data transmission is a key part in process control. The benefit offered by wireless network is appealing for process control. There are three layers of networks in a distributed process control system. Level one is between the smart devices and the controllers; level two is among the controllers and the workstations; and level three is from the workstations to the outside world. Wireless acts as a kind of network, and it can target any of the three network levels of a process control system. Level one requires reliable short-range data transmission. Data package sizes are small, usually less than 100 bytes. Of different wireless technologies, ZigBee, Wireless Fidelity, Bluetooth and Ultra Wideband work well at short range. Level two networks have longer transmission ranges and bigger data package sizes. Wireless as a new type of technology could introduce new support for a process control system.

This paper constitutes a work-in-progress report on the first, mostly conceptual phase of a major international effort in building and evaluating a distributed testbed for database application systems in safetycritical real-time environments. Given that safety/ reliability requirements and real-time constraints are in conflict there cannot be a closed form solution or design, and all system functions have to dynamically adapt to the unpredictable environmental situation in safety-critical real-time systems. Over the past years groups headed by the authors had pursued novel concepts and approaches on a novel tailored LINUX kernel, safety-critical application operating system support (MELODY project) and Active Database levels (concurrency control under data replication). In the research project a complete integration of these achievements from the basic OS kernel through the application levels is the major theme. While quite a number of research and design problems stemming from the partial insights or incomplete functionality on the various levels posed serious challenges the integration itself requires. and gives rise to, extensions, modifications, or refinements of the functions involved for ensuring system survivability. The paper will describe the technical details of these implications from the integration for the whole project as well as the stepwise design and evaluation of the different functions and models.- To our knowledge this is the first fully integrative attempts in the area of distributed safety-critical real-time systems.

While much recent work has focussed on the performance of transaction systems where individual transactions have deadlines, our research addresses the semantics of data usage in real-time applications and its integration with real-time resource management, in particular, the timeless value of real-time data and the inherent path and not state-based constraints on concurrency control. Central to our research is the idea of similarity which is a reflexive, symmetric relation over the domain of a data object. By exploiting the similarity relation, we propose a class of efficient data-access policies for real-time data objects. We shall also discuss the design of a distributed real-time data-access interface. Our goal is to build a database facility which can support predictable real-time applications involving high-speed communication, information access, and multimedia.

Scheduling analysis in real-time systems require an off-line feasibility (schedulability) test to guarantee the response time of critical tasks. There are fast and efficient tests for static schedulers. However, when a dynamic scheduler is required, the available tests are not as feast and efficient as static ones. In this paper, two different characterizations of feasible task sets are presented. These characterizations lead to an new feasibility algorithm. The proposed algorithm has an worst-case exponential complexity, but experimental results indicated that it runs on pseudo-polynomial time for a very large percentage of task sets. The algorithm also provides a sufficient condition for feasible asynchronous task sets. One of the main contributions of this work is the theoretical approach used to obtain the new feasibility test. The results of a large number of simulations, as well as, the theoretical demonstrations point out the improvements reached over previous tests.

This paper examines issues on how to predict timing behavior of rule-based decision systems for real-time applications. In particular, we focus on the analysis of response time of rule-based programs written in the production system language MRL. The design goal of MRL is to allow programmers to write OPS5-like rule-based programs in a language that is more amenable to formal analysis based on the semantic foundation underlying the language Unity. The language MRL, its analysis algorithms, and its execution system form a package of design tools for programming real-time rule-based decision systems.