David J. Abel

A comparative analysis of some two-dimensional orderings

Abstract Many spatial analysis algorithms for cellular representations and data structures are based on an ordering of cells or objects to transform a two-dimensional problem to a one-dimensional one. Several orderings are available and their differing properties influence the performance of the data structures and algorithms. The relative merits of five orderings (row, row prime, Hilbert, Morton and Gray code) are assessed empirically for four paradigmatic geographical data-processing tasks in spatial analysis and data management. It is concluded that the Hilbert ordering deserves further investigation.

The systems integration problem

Abstract The systems integration problem, defined as coupling GIS and other systems, is analysed by the use of two models based on database and federated database reference models. A three-schema model of a system enables the classification of incompatibilities between systems in terms of differences in external, conceptual and internal schemas. A systems reference model identifies transformation, constructor and accessor operations as the basic mechanisms to overcome these differences. The possible architectures of integrated systems are defined in terms of the presence of these operations and their general strengths and weaknesses are assessed.

Towards integrated geographical information processing

Many geographical applications access data from multiple disparate repositories such as file systems, Geographical Information Systems and database management systems which contain data able to be interrelated. Existing approaches that either built a single repository that contain all the required data or simply interconnect these repositories have not been well received. In this paper, we present the design of the Virtual GIS, a system for distributed spatial data processing in heterogeneous environments. The Virtual GIS is an integrated system that provides all the essential facilities for integrating and retrieving data from multiple component systems.The system isparticularly aimed at extensibility and scalability through distributing the processing load across the component systems and a global frontend. The object-oriented data model is adopted as a common data model to ensure meaningful data sharing. We also employ the fivelevel schema architecture of Sheth and Larson as the framework for system in...

Model and data integration and re-use in environmental decision support systems

This paper presents a software architecture for the management of environmental models. The Systems Theory representation of models is embedded in an object-oriented approach that emphasises the separation of models from data, thereby promoting model and data integration and re-use. The concepts presented here correspond to the requirements of a Model Management System (MMS). It is finally shown how a Decision Support System can use this approach to implement the MMS in order to facilitate problem definition (via the domain base) and problem solution (via the model base).

An exploration of GIS architectures for Internet environments

The World Wide Web and the Internet have great potential in improving accessibility to spatial data and to spatial data processing services. We explore this theme by reference to three recent developments, demonstrating different architectural approaches to spatial data distribution. First, the ACT Pilot system assesses the feasibility of transferring cadastral data over the Web in vector form, to facilitate interaction based around the map image. Secondly, the Hydra-4 project extends the vector-based map interaction for environmental mapping in an interactive system for water quality planning. Hydra-4 enables Web access to both spatial and temporal data. Thirdly, the on-going SMART project assesses the technical feasibility of spatial Internet marketplaces, in which applications are built from data and processing services offered by multiple, independent providers. A small SMART demonstrator system has been built.

Spatial Join Strategies in Distributed Spatial DBMS

In a distributed spatial database system, a user may issue a query that relates two spatial relations that are stored at different sites. Because of the sheer volume and complexity of spatial data, spatial joins between two spatial relations at different sites are expensive in terms of computation and transmission cost. In this paper, we examine the problems of spatial joins between sites, and present spatial join processing strategies used in a heterogeneous spatial database system. Preliminary experimental results are reported.

A framework for model integration in spatial decision support systems

Predictive simulation systems, embedding models of real-world processes, are usually designed as stand-alone computer packages. Users wishing to work on broader problems of extended scope need access to several models. This access can be provided by integrating several packages into a decision support system offering a coherent map-based problem-oriented interface to the under-lying models. This paper proposes the FMISDS integration approach that offers a problem-oriented method for designing the integrated system. It distinguishes syntactic and semantic issues in model integration, enabling a declarative description of the models and their conceptual relationships. The integration effort is supported by a reusable toolkit that interprets the declarative descriptions. FMISDS is demonstrated in a spatial decision support system for water catchment management.

SMART: Towards Spatial Internet Marketplaces

Spatial Internet Marketplaces are proposed as an extension to Spatial Data Infrastructures, in which on-line access to data and geoprocessing services replace distribution of data sets. A key design challenge is achieving interoperability in a large-scale distributed system with a high degree of heterogeneity in the services. The SMART (Spatial Marketplace) model combines a simple architectural model with only two types of services, a message-passing paradigm for interaction between customers and service providers, and a declarative language for expression of requests by a customer. The language, the Request Specification Language, is aimed at catering for variability in the operations offered by a service provider. It also ensures low complexity of implementation of mediators to connect existing information services to the Marketplace. A set of infrastructural services is proposed to aid a customer search for and combine services. The feasibility of the approach is confirmed by two proof-of-concept systems.

Environmental decision support system project: an exploration of alternative architectures for geographical information systems

Abstract Recent changes in information technology offer the opportunity to explore alternative architectures for geographical information systems (GIS) which might better support advanced applications. This paper describes the architecture and implementation of the environmental decision support system (EDSS), a prototype GIS tool kit. The architecture is based on a simple yet powerful systems model using only data collections, views and operations as the basic entity types. The design of the user interface, data management and data analysis within the model are outlined, with particular emphasis on the advanced facilities for which implementation is simplified by the architecture. A prototype applications system, BANKSIA, is also described.

Exploiting spatial indexes for semijoin-based join processing in distributed spatial databases

In a distributed spatial database system, a user may issue a query that relates two spatial relations not stored at the same site. Because of the sheer volume and complexity of spatial data, spatial joins between two spatial relations at different sites are expensive in terms of computational and transmission costs. In this paper, we address the problems of processing spatial joins in a distributed environment. We propose a semijoin-like operator, called the spatial semijoin, to prune away objects that do not contribute to the join result. This operator also reduces both the transmission and local processing costs for a later join operation. However, the cost of the elimination process must be taken into account, and we consider approaches to minimize these overheads. We also study and compare two families of distributed join algorithms that are based on the spatial semijoin operator. The first is based on multi-dimensional approximations obtained from an index such as the R-tree, and the second is based on single-dimensional approximations obtained from object mapping. We have conducted experiments on real data sets and report the results in this paper.