Stephen Kelley

Nearest neighbor queries

A frequently encountered type of query in Geographic Information Systems is to find the k nearest neighbor objects to a given point in space. Processing such queries requires substantially different search algorithms than those for location or range queries. In this paper we present an efficient branch-and-bound R-tree traversal algorithm to find the nearest neighbor object to a point, and then generalize it to finding the k nearest neighbors. We also discuss metrics for an optimistic and a pessimistic search ordering strategy as well as for pruning. Finally, we present the results of several experiments obtained using the implementation of our algorithm and examine the behavior of the metrics and the scalability of the algorithm.

MOCHA: a database middleware system featuring automatic deployment of application-specific functionality

Introduction MOCHA1 is a novel database middleware system designed to interconnect data sources distributed over a wide area network. MOCHA is built around the notion that the middleware for a large-scale distributed environment should be selfextensible. This means that new application-specific data types and query operators needed for query processing are deployed to remote sites in automatic fashion by the middleware system itself. In MOCHA, this is realized by shipping Java classes implementing these types or operators to the remote sites, where they can be used to manipulate the data of interest. All these Java classes are first stored in one or more code repositories from which MOCHA later retrieves and deploys them on a “need-to-do” basis. A major goal behind this idea of automatic code deployment is to fulfill the need for application-specific processing components at remote sites that do not provide them. MOCHA capitalizes on its ability to automatically deploy code to provide an efficient query processing service. By shipping code for query operators, MOCHA can produce efficient plans that place the execution of powerful data-reducing operators (filters) on the data sources. Examples of such operators are aggregates, predicates and data mining operators, which return a much smaller abstraction of the original data. In contrast, datainflating operators that produce results larger that their arguments are evaluated near the client. Since in many cases, the code being shipped is smaller than the data sets, automatic code deployment facilitates query optimization based on data movement reduction, which can greatly reduce query execution time. The architecture for MOCHA consists of four major components: Client Application an applet, servlet or Java ap-

Consistency and performance of concurrent interactive database applications

In many modern database applications, there is an emerging need for interactive environments where users directly manipulate the contents of the database. Graphical user interfaces (GUIs) display images of the database which must reflect a consistent up-to-date state of the data with minimum perceivable delay to the user. Moreover, the possibility of several applications concurrently displaying different views of the same database increases the overall system complexity. In this paper, we show how design, performance and concurrency issues can be addressed by adapting existing database techniques. We propose the use of suitable display schemas whose instances compose active views of the database, an extended client caching scheme which is expected to yield significant performance benefits, and a locking mechanism that maintains consistency between the GUIs and the database.

Integrating distributed scientific data sources with MOCHA and XRoaster

MOCHA is a novel middleware system for integrating distributed data sources that we have developed at the University of Maryland. MOCHA is based on the idea that the code that implements user-defined types and functions should be automatically deployed to remote sites by the middleware system itself. To this end, we have developed an XML-based framework to specify metadata about data sites, data sets, and user-defined types and functions. XRoaster is a graphical tool that we have developed to help the user create all the XML metadata elements to be used in MOCHA.

GDDT—A graphical design and documentation tool for software development

Abstract This paper describes “The Graphical Design and Documentation Tool” (GDDT), a general purpose support system for design and documentation. Self documentation and ease of use are presented as important criteria for such tools. Interactive graphics is introduced as a methodology for creating and maintaining hierarchical representations. The graphical representations of various requirements specification techniques and design tools are supported by an extended network model which supports hierarchical decomposition of structures. GDDT is proposed as a general purpose design tool which supports the most common logical constructions of both requirements specification and design methodologies and yet has a high level human interface which makes it easy to learn and use.