Gail Mitchell

The Aqua Data Model And Algebra

This paper describes a new object-oriented model and query algebra to be used as an input language for the query optimizers that are being built as a part of the EREQ project. The model adopts a uniform view of objects and values and separates syntactic, semantic, and implementation concerns. The algebra addresses issues of type-defined equality and duplicate elimination as well as extensions to bulk types other than sets.

PSGR: priority-based stateless geo-routing in wireless sensor networks

Volunteer forwarding, as an emerging routing idea for large scale, location-aware wireless sensor networks, recently has attracted a significant amount of research attention. However, several critical research issues raised by volunteer forwarding, including priority assignment, acknowledgement collisions and communication voids, have not been well addressed by the existing work. In this paper, we propose a priority-based stateless geo-routing (PSGR) protocol to address these issues. Based on PSGR, sensor nodes are able to locally determine their priority to serve as the next relay node using dynamically estimated network density. This effectively suppresses potential communication collisions without prolonging routing delays. PSGR also overcomes the communication void problem using two alternative stateless schemes, rebroadcast and bypass. We analyze energy consumption and delivery rate of PSGR as functions of transmission range. An extensive performance evaluation has been conducted to compare PSGR with competing protocols, including GeRaf, IGF, GPSR and flooding. Simulation results show that PSGR exhibits superior performance in terms of energy consumption, routing latency and delivery rate, and soundly outperforms all of the compared protocols

ProcessingWindow Queries in Wireless Sensor Networks

The existing query processing techniques for sensor networks rely on a network infrastructure for query propagation and data collection. However, such an infrastructure is very susceptible to network topology transients that widely exist in sensor networks. In this paper, we propose an infrastructure-free window query processing technique for sensor networks, called itinerary-based window query execution (IWQE), in which query propagation and data collection are combined into one single stage and executed along a well-designed itinerary inside a query window. We study the parameters for setting up an itinerary (e.g., width and route) and incorporate into IWQE three data collection schemes based on different performance trade-offs. Finally we demonstrate, by extensive simulations, the superior energy-time efficiency, robustness, and accuracy of IWQE over the current state-of-the-art techniques in supporting window queries under various network conditions.

Clock: synchronizing internal relational storage with external XML documents

In many business settings, a relational database system (RDBMS) will serve as the storage manager for data from XML documents. In such a system, once the XML data is dissembled and loaded into the storage system, XML queries posed against the (virtual) XML documents are processed by translating them into SQL queries against the relational storage. However, for applications which frequently update their XML documents, we cannot afford to reload a complete, possibly large, document for each update, instead we must be able to incrementally propagate document updates to the stored XML data. We address the issue of correctly reflecting updates of external XML documents into the loaded XML data in a relational database system. We describe Clock, a framework for synchronizing the relational storage with updated XML documents by exploiting a metadata-driven technology. First, we propose a set of (DTD preserving) update primitives for XML documents. Second, based on the mapping between XML and the relational model, we describe the propagation of those update primitives. Validation of the updates ensures they will not violate the constraints specified by the DTD. We have implemented a working prototype of the Clock system using the IBMs XML4J parser JDBC 2 and Oracle 81. We report on preliminary experiments conducted using this prototype to analyze our algorithms in a document update setting.

Sangam - a solution to support multiple data models, their mappings and maintenance

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An architecture for query processing in persistent object stores

Query optimizers for persistent object systems should be extensible to react to user-supplied abstract types. Current architectures support only a single, non-extensible technique for controlling the optimization process. The authors propose an alternative to the current extensible architectures that will support multiple optimizer control strategies and the addition of new control strategies. The optimizer consists of a collection of optimization regions, each of which can transform queries according to a particular control strategy, set of transformations and cost model. A global optimizer control coordinates the movement of a query between these regions. This architecture provides extensibility in the optimizers repertoire of control strategies through the addition of new regions. The authors describe their approach and demonstrate its utility by following the optimizer as it works on an example query. The optimizer will move the query between three distinct regions. The different regions illustrate different kinds of transformations and different strategies for application of those transformations.<<ETX>>

CME: A Contour Mapping Engine in Wireless Sensor Networks

Contour maps, showing topological distribution of extracted features, are crucial for many applications. Building a dynamic contour map in a wireless sensor network is a challenging task due to the constrained network resources. In this paper, we present the design of a contour mapping engine (CME) in wireless sensor networks. Our design incorporates in-network processing based on binary classification to reduce the total number of active nodes. The underlying network architecture is analyzed to derive an optimal configuration. We show, by extensive simulations, the superiority of CME over the state-of-the-art contour mapping techniques.

A framework for TMN-CORBA interoperability

The Telecommunications Management Network (TMN) Architecture model is the de facto standard for the telecommunications industry; it plays an influential role in development of telecommunications-related systems. On the other hand, the Common Object Request Broker Architecture (CORBA) model, aimed at the development and integration of distributed systems, has matured and gained importance over the past few years and thus will be influential in the development of general application systems. In this paper, we study the interoperability issues between systems based on these models because of their relevance to integrated telecommunications enterprises. For example, billing can require interactions between OSI-based systems supporting usage measurement and CORBA-based systems managing customer profiles and financial activities. We first introduce a framework for comparing different architectures. This framework identifies key characteristics of architectural models as well as areas where inter-model mappings may be required. We examine the TMN and CORBA models in the context of this framework, then explore some of the issues in providing interoperability between TMN-based and CORBA-based systems. This exploration is guided by the the framework comparison points. Finally, we conclude the paper with a discussion of future work.

Energy-Aware and Time-Critical Geo-Routing in Wireless Sensor Networks

Volunteer forwarding, as an emerging routing idea for large scale, location-aware wireless sensor networks, has recently received significant attention. However, several critical research issues raised by volunteer forwarding, including communication collisions, communication voids, and time-critical routing, have not been well addressed by the existing work. In this paper, we propose a priority-based stateless geo-routing (PSGR) protocol that addresses these issues. Based on PSGR, sensor nodes are able to locally determine their priority to serve as the next relay node using dynamically estimated network density. This effectively suppresses potential communication collisions without prolonging routing delays. PSGR also overcomes the communication void problem using two alternative stateless schemes, rebroadcast and bypass. Meanwhile, PSGR supports routing of time-critical packets with different deadline requirements at no extra communication cost. Additionally, we analyze the energy consumption and the delivery rate of PSGR as functions of the transmission range. Finally, an extensive performance evaluation has been conducted to compare PSGR with competing protocols, including GeRaf, IGF, GPSR, flooding, and MSPEED. Simulation results show that PSGR exhibits superior performance in terms of energy consumption, routing latency, and delivery rate, and soundly outperforms all of the compared protocols.

Optimization of Object-Oriented Queries: Problems and Approaches

An object-oriented data model can support features such as abstract data types, methods, encapsulation, subtyping (or inheritance), complex structures, and object identity. The processing of queries in such a model must incorporate support for these features. Query optimization will require new techniques for supporting the object-oriented features. Although some of the problems that must be solved by an object-oriented query optimizer are similar to problems solved by relational and extensible optimizers, there are also many problems that are unique to the object-oriented data model.