Michael Freeston

A general solution of the n-dimensional B-tree problem

We present a generic solution to a problem which lies at the heart of the unpredictable worst-case performance characteristics of a wide class of multi-dimensional index designs: those which employ a recursive partitioning of the data space. We then show how this solution can produce modified designs with fully predictable and controllable worst-case characteristics. In particular, we show how the recursive partitioning of an n-dimensional dataspace can be represented in such a way that the characteristics of the one-dimensional B-tree are preserved in n dimensions, as far as is topologically possible i.e. a representation guaranteeing logarithmic access and update time, while also guaranteeing a one-third minimum occupancy of both data and index nodes.

Advances in the Design of the BANG File

A recent paper described a new kind of grid file — the BANG file — which, unlike previous grid file designs, has the important property that the directory never expands faster than the data, whatever the dimensionality of the file or the form of the data distribution. Experience with the first implementation of the BANG file has given new insights into its properties and behaviour, which have enabled significant improvements in performance to be obtained without compromising the conceptual simplicity of the original design: •access to an individual tuple now always succeeds in a single pass down the directory tree, as with a B-tree; •overflow or underflow of data or directory pages never leads to more page splits or merges than in a B-tree of the same directory depth; •every direct representation of a sub-space of the data space is guaranteed to be a minimal representation — substantially improving the efficiency of range searches, partial match searches and joins.

The Alexandria Digital Library Architecture

Since 1994, the Alexandria Digital Library Project has developed three prototype digital libraries for georeferenced information. This paper describes the most recent of these efforts, a three-tier client-server architecture that relies heavily on a middleware layer to present a single uniform set of interfaces to multiple heterogeneous servers. These standard interfaces, all of which are implemented in HTTP, support session management, collection discovery and evaluation, metadata searching, metadata retrieval, and online holding retrieval. An XML-based metadata encoding scheme and a simple boolean query language have also been developed. The architecture described by these interfaces has been implemented at UCSB.

Scalable access within the context of digital libraries

Abstract. This paper presents a summary of some of the work-in-progress within the Alexandria Digital Library Project. In particular, we present scalable methods for locating information at different levels within a distributed digital library environment. Starting at the high level, we show how queries can be routed to appropriate information sources. At a given source, efficient query processing is supported by using materialized views and multidimensional index structures. Finally, we propose solutions to the problem of storage and retrieval of large objects on both secondary and tertiary storage devices.

Visual Explorations for the Alexandria Digital Earth Prototype

The Alexandria Digital Earth Prototype project addresses issues of access, browsing, delivery and understanding of georeferenced library items. Two visualization approaches that address these issues in different ways are under development: interfaces between some existing digital earth systems and the digital library, and spatial but nongeoreferenced information spaces. Both the abstract spatial and georeferenced projects are being evaluated for their educational potential in classroom and lectures, in labs and as tools for students to use on their own.

A well-behaved file structure for the storage of spatial objects

A dynamic file structure for spatial object storage and access is described. Based on an extension of the BANG file, it has a self-balancing, tree-structured directory with the following properties:

The ADEPT Concept-Based Digital Learning Environment

We describe the design and application of a Digital Learning Environment (DLE) that is integrated with the collections and services of the Alexandria Digital Library (ADL). This DLE is in operational use in undergraduate teaching environments. Its design and development incorporate the assumption that deep understanding of both scientific phenomena and scientific methods is facilitated when learning materials are explicitly organized, accessed and presented at the level of granularity of appropriate sets of scientific concepts and their interrelationships. The DLE supports services for the creating, searching, and displaying: (1) knowledge bases (KBs) of strongly structured models of scientific concepts; (2) DL collections of information objects organized and accessible by the concepts of the KBs; and (3) collections of presentation materials, such as lectures and laboratory materials, that are organized as trajectories through the KB of concepts.

On the Complexity of BV-tree Updates

We have shown in this paper how logarithmic exact-match access and update complexity can be maintained in a BV-tree representation. The price paid for guaranteed dynamic performance (i.e. performance which does not degrade over time for a given data set) is that the demotion of entries which no longer represent guards may be postponed. In the worst case this could require a substantial increase in the size of higher level index nodes in order to maintain a constant level of performance for a given data set.

DialogPlus: digital libraries in support of innovative approaches to learning and teaching in geography

Summary form only given. DialogPlus is one of four international projects, supported in the US by the NSF International Collaborative Research Program in Digital Libraries, and in the UK by the Joint Information Systems Committee of the UK Higher Education Funding Councils. The two primary objectives of the project are to develop: a distributed enabling information infrastructure for the support of learning and teaching in geography; innovative approaches to teaching and learning, based on this infrastructure. Specifically, the project the undergraduate and postgraduate programs of study in geography in the consortium universities can be enriched and developed through cross-national collaboration and online delivery; different virtual learning environments can be supported by a common, open and distributed digital library infrastructure; major geospatial resources relevant for the study of the environment and landscape and for the study of human populations in cities and the countryside can be used in student programs of study; important skills in the analysis of spatial information through use of Geographical Information Science and Earth Observation software and functions can be taught online and made available in undergraduate programs.