Multiclass Transaction Scheduling and Overload Management in Firm Real-Time Database Systems
Real-Time Database Systems (RTDBSs), have attracted considerable amount of research attention in the recent past and a number of important applications have been identified for such systems, such as telecommunications network management, automated air traffic control, automated financial trading, process control and military command and control systems. Due to the rapidity of change of the system state in such applications, as well as the inherent complexities in controlling such systems (which result in frequent violation of consistency requirements and consequent repeated firings of control actions), it is likely that the transaction load in these systems would be fairly high. Thus RTDBSs need to be equipped with overload management mechanisms. Unfortunately overload management has been a fairly neglected area in real-time systems research in general and real-time database research in particular. In this paper we introduce Adaptive Access Parameter (AAP), a scheduling mechanism for multiclass transactions in real-time database systems that employs an explicit admission control policy to manage overload as well as system bias towards particular transaction classes. We show the theoretical underpinnings behind AAP and then report a thorough performance study that demonstrates AAP's substantial superiority over current algorithms with regard to performance metrics as well as computational overhead.

title: Buffer management in real-time active database systems
abstract: Real-time, active database systems (RTADBSs) have attracted the attention of researchers in recent times. Such systems are envisioned as control systems for environments as diverse as process control, network management and automated financial trading. Sensors distributed throughout the system report the state of the system to the database. Unacceptable state reports typically result in corrective actions being triggered with deadlines. Thus RTADBSs incorporate both real-time as well as active characteristics. In this paper we study buffer management in RTADBSs. Buffer management is recognized as not being a well studied area in real-time systems. As a result of our work, we postulate (Prefetching Anticipatorily and Priority basEd Replacement) (PAPER), a new buffer management scheme that relies on two strategies: prefetching and priority based buffer replacement. We report the result of studies of the performance of PAPER, as compared to that of existing buffer management algorithms. The insights derived from this paper impact both real-time database systems as well as RTADBSs.

title: Handling Sensor Data in Rapidly Changing Environments to Support Soft Real-Time Requirements
abstract: Databases have been mandated as the chosen platform to develop automated control systems for environments where the state of the system changes rapidly and actions need to be taken with timing constraints, for example, stock trading, air traffic control, network management, and process control to name a few. Input data in such systems come from sensors distributed throughout the physical environment being monitored. As the system state changes rapidly, the sensors report information fast and with high volumes. Control decisions in such systems are highly dependent on the accuracy and timeliness of such recorded sensor-reported data. In this paper we suggest ways to algorithmically maintain the accuracy and timeliness of sensor data by enforcing two properties termedrecency andtemporal consistency. Simultaneously, our algorithms also attempt to satisfyquality of service requirements on response times of queries submitted in such systems. The performance of these algorithms is validated through an extensive simulation.

title: MANDATE: MAnaging Networks Using DAtabase TEchnology
abstract: There has been a growing demand for the development of tools to manage enterprise communication networks. A management information database is the heart of a network management system-it provides the interface between all functions of the network management system and, therefore, has to provide sophisticated functionality allied with high performance. The authors introduce the design of MANDATE (MAnaging Networks using DAtabase TEchnology), a proposed database system for effectively supporting the management of large enterprise networks. The MANDATE design makes a conscious attempt to take advantage of the special characteristics of network data and transactions, and of advances in database technology, to efficiently derive some of the required management functionality.

title: Buffer management in real-time active database systems
abstract: Real-time active database systems (RTADB) have attracted the attention of researchers in recent times. Such systems are envisioned as control systems for environments as diverse as process control, network management and automated financial trading. Sensors distributed throughout the system report the state of the system to the database. Unacceptable state reports typically results in corrective actions being triggered with deadlines. Thus RTADB's incorporate both real-time as well as active characteristics. We study buffer management in RTADB. Buffer management is recognized as not being a well studied area in real-time systems. As a result of our work, we postulate PAPER, a new buffer management scheme that relies on two strategies: prefetching and priority based buffer replacement. We report the result of studies of the performance of PAPER, as compared to that of existing buffer management algorithms. The insights derived from this paper impact both real-time database systems as well as real-time, active database systems.

title: Providing Real-Time Response, State Recency and Temporal Consistency in Databases for Rapidly Changing Environments
abstract: Databases have been proposed as the chosen platform to develop automated control systems for environments where the state of the system changes rapidly, and actions need to be taken with timing constraints, such as stock trading, air traffic control, network management and process control. The workload in such systems consists primarily of two types: (a) updates , which report the state of the environment to the database and arrive very frequently, and (b) transactions which arrive with deadlines. In this paper we develop algorithms to install these updates rapidly enough to ensure “state recency” while allocating sufficient resources to transactions to minimize tardiness. We also require that these transactions read temporally consistent data. In summary, this paper contributes in the following three interrelated issues: 1. 1. First and foremost, we look at some interesting problems regarding amalgamating temporal and real-time databases. 2. 2. We look at simultaneous satisfaction of state recency and temporal consistency which are central issues in the class of systems considered in this paper, i.e., rapidly changing systems. 3. 3. We design algorithms that attempt to achieve equilibrium with regard to the conjoint processing of frequently arriving state updates and time constrained transactions.

title: Jigsaw Texture Synthesis
abstract: Texture synthesis aims to seamlessly extend a sample texture. This can be achieved by reproducing the texture's recognisable patterns along with minimising the occurrences of undesirable image characteristics such as disjoint image features. Presently, patch-based methods have consistently produced the most impressive results. These methods involve aligning and stitching texture patches together. However, image inconsistencies exist when image features are misaligned; they are either fused together or abruptly cut off. Our method minimises the occurrences of these anomalies by using image edges to align patches and redefine their boundaries to preserve texture features. This implementation requires little to no user-defined variables or iterations and can be practically scalable given some pre-computation.

title: Self-stabilizing wormhole routing on ring networks
abstract: Wormhole routing is the most common in parallel architecture in which messages are sent in small fragments called flits. It is a lightweight and efficient method of routing messages between parallel processors. Self-stabilization is a technique that guarantees tolerance to transient faults (e.g. memory corruption or communication hazard) for a given protocol. Self-stabilization guarantees that the network recovers to a correct behavior infinite time, without the need for human intervention. Self-stabilization also guarantees the safety property, meaning that once the network is in a legitimate state, it will remain there until another fault occurs. This paper presents the first self-stabilizing network algorithm in the wormhole routing model, using the unidirectional ring topology. Our solution benefits from wormhole routing by providing high throughput and low latency, and front self-stabilization by ensuring automatic resilience to all possible transient failures.

title: Self-stabilizing mutual exclusion using unfair distributed scheduler
abstract: A self-stabilizing algorithm, regardless of the initial system state, converges infinite time to a set of states that satisfy a legitimacy predicate without the need for explicit exception handler of backward recovery. Mutual exclusion is fundamental in the area of distributed computing, by serializing the accesses to a common shared resource. All existing probabilistic self-stabilizing mutual exclusion algorithms designed to work under an unfair distributed scheduler suffer from the following common drawback: Once stabilized, there exists no upper bound of time between two executions of the critical section at a given node. We present the first probabilistic self-stabilizing algorithm that guarantees such a bound (O(n/sup 3/), where n is the network size) while working using an unfair distributed scheduler. As the scheduling adversary gets weaker the bound gets better. Our algorithm works in an anonymous unidirectional ring of any size and has a O(n/sup 3/) expected stabilization time.

title: Publish/subscribe scheme for mobile networks
abstract: The information dissemination in mobile networks is an important but complex and challenging problem. Designing suitable communication primitives for these systems is critical. One of these primitives is the publish/subscribe paradigm. The publish/subscribe is a strategy to establish communication between the information providers (publishers) and information consumers (subscribers) in a distributed system. Our work focuses on an appropriate distributed infrastructure suitable for a scalable implementation of a publish/subscribe system. We present a formal model which is adapted for the peer-based particular subscription criteria of publish/subscribe systems. Moreover, we propose a general deterministic information diffusion scheme for mobile systems. The three main features of our communication scheme are the following: First, our scheme is well-adapted to scalable systems without compromising any subscription criteria or network reorganization. Second, we maintain the anonymity of the distributed system --- in order to maintain the network structure, we need only local information. Third, our solution is fully decentralized and modular, thus making it appropriate for practical implementations.

title: External control in Markovian genetic regulatory networks
abstract: Probabilistic Boolean networks (PBN's) have been recently introduced as a rule-based paradigm for modeling gene regulatory networks. Such networks, which form a subclass of Markovian genetic regulatory networks, provide a convenient tool for studying interactions between different genes while allowing for uncertainty in the knowledge of these relationships. This paper deals with the issue of control in probabilistic Boolean networks. More precisely, given a general Markovian genetic regulatory network whose state transition probabilities depend on an external (control) variable, the paper develops a procedure by which one can choose the sequence of control actions that minimize a given performance index over a finite number of steps. The procedure is based on the theory of controlled Markov chains and makes use of the classical technique of dynamic programming. The choice of the finite horizon performance index is motivated by cancer treatment applications where one would ideally like to intervene only over a finite time horizon, then suspend treatment and observe the effects over some additional time before deciding if further intervention is necessary. The undiscounted finite horizon cost minimization problem considered here is the simplest one to formulate and solve, and is selected mainly for clarity of exposition, although more complicated costs could be used, provided appropriate technical conditions are satisfied.