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SCHEMA TRANSLATIONS BY XSLT FOR GML-ENCODED GEOSPATIAL DATA IN 
HETEROGENEOUS WEB-SERVICE ENVIRONMENT 
L. Lehto and T. Sarjakoski 
Finnish Geodetic Institute, PO Box 15, 02431 Masala, Finland - (Lassi.Lehto, Tapani.Sarjakoski)@fgi. fi 
Commission IV, WG IV/2 
KEY WORDS: Web based, Integration, Interoperability, Mobile, Internet 
ABSTRACT: 
The paper discusses online integration of XML-encoded datasets in the current Web services environment, especially concentrating 
on the required schema transformations. The approach is based on the use of a generic XML transformation technology, called 
Extensible Stylesheet Language Transformations (XSLT). The role of the data integration process in a layered service architecture 
framework is described. The basics of the applied XML technology are introduced. A case implementation, built as the prototype 
service of the GiMoDig project, demonstrates the benefits yielded by the approach. The required schema translations can be carried 
out as a single process, together with the needed coordinate transformations. The same base methodology can be applied both to 
query and data transformations. The declarative nature of the transformation definition, represented as templates stored in an XML- 
encoded text file, makes the transformation process easy to debug and fine-tune. As the final result, cross-border map visualization is 
presented. 
1. INTRODUCTION 
Integration of distributed geospatial databases is a rather well 
established research area. Many solutions have been proposed 
over the years, based on various database tools and 
technologies. The recent development of the Web as a common 
platform for geospatial data delivery and processing makes the 
traditional problem of database integration to emerge in a new 
setting. 
Simple Web-based map services have become commonplace. 
As more sophisticated service types are being introduced, the 
focus in research and development is shifting away from issues 
related to pure map visualization to processes involving real 
spatial datasets. Extensible Markup Language (XML) based 
data encoding has been widely adopted in various application 
areas, geographic information not being an exception (W3C, 
2004a) (Lehto, 2000). Geography Markup Language (GML) is 
a well-known XML vocabulary designed for applications 
dealing with geospatial data (OGC, 2003). 
The new challenge encountered in this approach is to integrate 
XML-encoded heterogeneous geospatial datasets in real-time. 
The data integration process involves at least two aspects: 
schema translations and coordinate system transformations. 
These two integration tasks are dealt with in the following. The 
issues are discussed in the context of a seamless, cross-border 
mobile map service, based on open system architecture. 
In this paper the need for real-time data transformations is first 
motivated and the chosen general service architecture 
introduced. The applied generic XML transformation 
technology is then discussed. Finally, as a case implementation 
a prototype cross-border GML data service developed by a 
four-nation EU-funded project: "Geospatial Info-Mobility 
Service by Real-Time Data-Integration and Generalisation", 
(GiMoDig, 2004) is presented. 
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2. NEED FOR DATA INTEGRATION 
The rapidly expanding European integration. development 
increases the demand for consistent, continent-wide geospatial 
data services. A few European Commission-backed initiatives 
are already working to facilitate this process. These initiatives 
include projects like GINIE, GETIS, EULIS, INSPIRE, 
GiMoDig etc. Various data harmonization processes of the 
EuroGeographics also aim at same target. The main results of 
this work can be seen in the development of the European-wide 
datasets, like EuroGlobalMap, EuroRegioMap and SABE 
(EuroGeographics, 2004). 
In the case of the major national datasets, like the topographic 
map series, it has become obvious that the Pan-European 
geospatial data provision must be based on databases 
maintained in the national data models by the national 
authorities. Standardized access interfaces and spatial data 
encoding mechanisms would be applied to achieve the desired 
cross-border accessibility. The INSPIRE Architecture and 
Standards Position Paper (INSPIRE, 2004) proposes that the 
OGC's implementation level specification Web Feature Service 
(WFS, 2003), or rather the upcoming ISO-released official 
version of it, be used as a query interface by the data providers. 
According to the WFS specification, the dataset provided by the 
service is to be encoded in XML format - in compliance with 
the GML specification of the OGC. 
In the case of the proposed European geospatial data service 
architecture there are two basic integration tasks. Firstly, the 
coordinate values presented in the individual national 
coordinate systems have to be transformed into a common Pan- 
European reference frame. Secondly, the data models applied in 
each country for comparable data contents, like the information 
normally presented on large-scale topographic maps, vary 
considerably from country to country. This fact necessitates