35880312
Priority assignment in real-time active databases
Active databases and real-time databases have been important areas of research in the recent past. It has been recognized that many benefits can be gained by integrating active and real-time database technologies. However, there has not been much work done in the area of transaction processing in active real-time databases. This paper deals with an important aspect of transaction processing in active real-time databases, namely the problem of assigning priorities to transactions. In these systems, time-constrained transactions trigger other transactions during their execution. We present various policies for assigning priorities to parent, immediate and deferred transactions executing on a multiprocessor system and then evaluate the policies using simulation. The simulator has been validated by comparing to three sets of published results. Our new results demonstrate that dynamically changing the priorities of transactions depending on their behavior (triggering rules), yields a substantial improvement in the number of triggering transactions that meet their deadline.<<ETX>>
12618619
Real-Time Operating Systems
Real-time operating systems are an integral part of complex real-time systems. Three general categories of real-time operating systems exist: small, proprietary kernels, real-time extensions to commercial timesharing operating systems, and research kernels. This paper discusses each of these areas focusing on how each of these classes deal with predictability. It is argued that the small, proprietary kernels are predictable, but offer little help to the real-time systems designer and implementor in producing predictable applications. Real-time versions of commercial operating systems like UNIX and Mach offer greater implementation support, but are, in general, NOT predictable themselves nor offer enough support to applications which require predictability. This, of course, does not mean that there is no way to achieve predictability with these operating systems. It is possible to achieve predictability by very careful design, by using a very limited subset of the overall features provided, and by proving that the features being used for predictability cannot in any way be impacted by any other part of the system. Finally, research kernels are attempting to provide greater design, implementation and evaluation support together with predictability for both the operating system and the application.
13909231
The many faces of multi-level real-time scheduling
Many real-time scheduling algorithms use simplistic sets of assumptions and this limits their applicability in practice. Often, a large real-time system has multiple scheduling algorithms and multi-level scheduling algorithms. Multiple algorithms arise when it is possible to partition the system into subsystems, each with their own algorithm. While this is a valuable approach, in this paper we focus on the issue of multi-level scheduling. Multi-level scheduling arises for various important reasons. In this invited presentation we discuss multi-level scheduling examples from a process/thread model, local/distributed scheduling, manufacturing, and multimedia.
20106864
Priority assignment in real-time active
databases

Abstract.
Active databases and real-time databases
have been important areas of research
in the recent past. It has been recognized
that many benefits can be gained by
integrating real-time and active database technologies.
However, not much work has been
done in the area of transaction processing in real-time active
databases. This paper deals with an important aspect
of transaction processing
in real-time active databases, namely the problem of
assigning priorities to
transactions. In these systems, time-constrained
transactions trigger other
transactions during their execution. We present three policies for assigning
priorities to parent, immediate and deferred transactions executing on a
multiprocessor system and then evaluate the policies through simulation. The
policies use different amounts of semantic information about transactions to
assign the priorities. The simulator has been validated against the results of
earlier published studies. We conducted experiments in three settings: a task
setting, a main memory database setting and a disk-resident database
setting.
Our results demonstrate that dynamically changing the priorities of
transactions, depending on their behavior (triggering rules), yields a
substantial improvement in the number of triggering transactions that meet
their deadline in all three settings.

11178551
A spatiotemporal communication protocol for wireless sensor networks
In this paper, we present a spatiotemporal communication protocol for sensor networks, called SPEED. SPEED is specifically tailored to be a localized algorithm with minimal control overhead. End-to-end soft real-time communication is achieved by maintaining a desired delivery speed across the sensor network through a novel combination of feedback control and nondeterministic geographic forwarding. SPEED is a highly efficient and scalable protocol for sensor networks where the resources of each node are scarce. Theoretical analysis, simulation experiments, and a real implementation on Berkeley motes are provided to validate the claims.
920081
Energy-efficient surveillance system using wireless sensor networks
The focus of surveillance missions is to acquire and verify information about enemy capabilities and positions of hostile targets. Such missions often involve a high element of risk for human personnel and require a high degree of stealthiness. Hence, the ability to deploy unmanned surveillance missions, by using wireless sensor networks, is of great practical importance for the military. Because of the energy constraints of sensor devices, such systems necessitate an energy-aware design to ensure the longevity of surveillance missions. Solutions proposed recently for this type of system show promising results through simulations. However, the simplified assumptions they make about the system in the simulator often do not hold well in practice and energy consumption is narrowly accounted for within a single protocol. In this paper, we describe the design and implementation of a running system for energy-efficient surveillance. The system allows a group of cooperating sensor devices to detect and track the positions of moving vehicles in an energy-efficient and stealthy manner. We can trade off energy-awareness and surveillance performance by adaptively adjusting the sensitivity of the system. We evaluate the performance on a network of 70 MICA2 motes equipped with dual-axis magnetometers. Our results show that our surveillance strategy is adaptable and achieves a significant extension of network lifetime. Finally, we share lessons learned in building such a complete running system.