The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Real-Time Content Transformations in a Web Service-Based Delivery Architecture for Geographic Information

Lassi Lehto

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Surveying for public examination and debate in Auditorium M1 at Helsinki University of Technology (Espoo, Finland) on the 14th of December, 2007, at 12 noon.

Overview in PDF format (ISBN 978-951-711-272-7)   [1637 KB]
Dissertation is also available in print (ISBN 978-951-711-271-0)

Abstract

The proliferation of location-aware consumer applications is increasing the demand for Web service-based delivery of geospatial content. Significant national and European-wide initiatives have been launched to develop Spatial Data Infrastructures (SDI) aiming at more efficient dissemination of public-sector geodata resources. These frameworks largely depend on the availability of online services and datasets. At the same time, geodata-related network solutions are becoming more sophisticated, due to the gradual introduction of feature-based representations of geographic information into the Web application domain. Along with the growing number of different application areas and content resources involved, the diversity challenges related to client platforms and source databases have also increased.

The interoperability opportunities provided by the broad adoption of Web standards, on one hand, and the societal pressure created by the diverse needs of the wide consumer use base and public sector efficiency requirements, on the other, create the framework within which the present study was conducted. One central goal is the broad application of general-purpose Web methodologies to problems encountered in the geospatial computing domain. The research aimed to resolve the heterogeneity challenges by real-time content transformations, applied in a network service-based delivery architecture. The present thesis focuses on three particular applications of real-time content transformation: multi-purpose publishing, on-the-fly generalisation and schema transformation. These processes are carried out in a distributed multi-tier service architecture framework, designed in the study.

The results of the study confirm the applicability of generic stylesheet-based mechanisms for platform-specific geodata visualisation. On-the-fly generalisation is found to be a valuable tool for creating highly personalised map displays in which dynamic context parameters, such as the current location of the user, can be taken into account. The study proved real-time schema transformations to be a feasible solution for ensuring the dynamic service-level interoperability of heterogeneous source databases. The declarative way used to configure the transformations proved to be especially beneficial, enabling two-way query and data transformations to be defined using the same base methodologies.

A service architecture framework for advanced geospatial Web applications was designed in the study. This six-tier architecture consists of the following conceptual service layers, each with a well-defined responsibility in the service provision: a data service layer, data integration layer, data processing layer, portal layer, value-adding service layer and client layer. Open standardised service interfaces are used throughout the architecture framework.

The three real-time content transformation types were successfully implemented in the extensive service platform developed in the EU-funded GiMoDig project. In this test environment topographic base datasets from four countries (Denmark, Finland, Germany, Sweden) are integrated by means of a two-way real-time schema transformation. The resulting harmonised dataset is further processed by an on-the-fly generalisation process, which adjusts it to the actual presentation scale and use case. Finally, the dataset is transformed into a visual map by an online multi-purpose publishing process, taking the particularities of the used client device into account. The final result is a seamless cross-border map service capable of real-time integration of heterogeneous source datasets and of dynamic adaptation to various different use platforms.

This thesis consists of an overview and of the following 6 publications:

  1. Kähkönen, J., Lehto, L., Kilpeläinen, T. and T. Sarjakoski, 1999. Interactive visualisation of geographical objects on the Internet. International Journal of Geographical Information Science, Special Issue, 13 (4): 429-438.
  2. Lehto, L., 2003. A standards-based architecture for multi-purpose publishing of geodata on the Web. In: Peterson, M. P. (ed.), Maps and the Internet, Elsevier Science, pp. 221-230.
  3. Lehto, L. and T. Sarjakoski, 2005. XML in service architectures for mobile cartographic applications. In: Meng, L., Zipf, A. and T. Reichenbacher (eds.), Map-based Mobile Services – Theories, Methods and Implementations, Springer Berlin Heidelberg New York, pp. 173-192.
  4. Lehto, L. and T. Sarjakoski, 2004. Schema translations by XSLT for GML-encoded geospatial data in heterogeneous Web-service environment. Proceedings of the XXth ISPRS Congress, July 2004, Istanbul, Turkey, International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, XXXV (B4/IV): 177-182, also CD-ROM. © 2004 by authors.
  5. Lehto, L. and L. T. Sarjakoski, 2005. Real-time generalization of XML-encoded spatial data for the Web and mobile devices. International Journal of Geographical Information Science, Special Issue, 19 (8-9): 957-973.
  6. Lehto, L., 2007. Schema translations in a Web service based SDI. Proceedings of the 10th AGILE International Conference on Geographic Information Science, The European Information Society: Leading the way with geo-information, May 8-11, 2007, Aalborg, Denmark, CD-ROM.

Keywords: Internet GIS, transformation service, schema transformation, service architecture

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© 2007 Helsinki University of Technology

Last update 2011-05-26