Publishing geospatial data through geospatial web service and XML database system

American Journal of Applied Sciences, Oct, 2008 by Pouria Amirian, Ali A. Alesheikh

INTRODUCTION

Majority of geospatial processing systems require some level of interoperability as a fundamental capability. Based on OGC Reference Model (1), spatial interoperability refers to capability to communicate, execute programs, or transfer geospatial data among various functional units in a manner that requires the user to have little or no knowledge of the unique characteristics of those units. Therefore, non-interoperability of geospatial processing systems prevents sharing of geospatial data and services among software applications. Spatial interoperability faces two main challenges; syntactic heterogeneity and semantic heterogeneity (2). Syntactic heterogeneity which is the result of differences in storage formats and software incompatibility is a technical issue and can be addressed by technical means. Semantic heterogeneity arises as a result of incompatibility in meanings of data. Addressing syntactic heterogeneity is the main concern of this research.

Syntactic heterogeneity of geospatial information systems can be categorized in data and access heterogeneity. In data heterogeneity geospatial processing systems use various internal proprietary data formats. To share geospatial data, converters and/or transfer formats must be developed, which is a resource and time consuming task. In addition, there are so many different standards for geospatial data that converting various data formats can itself become a barrier to interoperability.

Access heterogeneity restricts inter-process communication among various geospatial processing systems, since different vendors' geospatial processing systems use proprietary software access methods with proprietary software interfaces. In other words, interface definition languages, communication protocols, communication ports and even object transfer mechanisms, varies in each software development platform. So the software platform which has been used to develop the geospatial processing system imposes the use of specific and proprietary communication methods among various parts of the system. For this reason, different geospatial processing systems that have been developed by different software development platforms, cannot communicate and share services automatically and in an interoperable manner.

In GIS community, OGC has introduced specific kind of online services, to overcome spatial non-interoperability problem. These services which are called OGC geospatial Web services (or geospatial Web services for short) have been developed with the goal of sharing geospatial data and services among heterogeneous geospatial processing systems. Web Feature Service (WFS) and Web Map Service (WMS) are the most fundamental geospatial Web services which are introduced by OGC. At the same time, in Information Technology (IT) world, the best solution for providing interoperability among heterogeneous software systems in distributed and decentralized environments are Web services technologies (3).

Geospatial Web services and Web services differ in a way that Web services are composed of particular set of technologies and protocols but Geospatial Web services are comprised of defined set of interface implementation specifications which can be implemented with diverse technologies (4).

With respect to above description, it is suggested that making use of Web services technologies as enabling infrastructure for implementing geospatial Web services would significantly facilitate sharing geospatial data as well as access to processing services from multiple resources in and out of GIS community. In other words, geospatial Web services which are developed using Web services technologies can provide access interoperability among various geospatial and non-geospatial processing systems. Furthermore, using open and platform independent data standards like GML, data interoperability can also be achieved. Meanwhile, proper management of geospatial data necessitates use of efficient and optimized data management systems. In this context, considering the nature of GML as an XML-based standard, using XML database systems is suggested for facilitating and improving geospatial data management. This research describes development of a Geospatial Web service using Web Services Technologies and XML database systems to achieve spatial interoperability, while having a proper management on spatial data over the web. Since there are two technologies for XML data management, in the context of developed geospatial Web service, practical evaluation of two technologies illustrated as well. The study first explains Web services technologies, geospatial Web services and XML database systems. Afterwards design and development of a geospatial Web service is discussed. Finally practical test and its outcomes illustrated.

WEB SERVICES PLATFORM

Web services are self-contained, self-describing, modular applications that can be published, located and invoked across the Web and perform functions that can be anything from simple requests to complicated business processes (5). Web Services are the basic components of distributed service-oriented systems. The World Wide Web Consortium (W3C) defines Web Services as a software system designed to support machine-to-machine interaction over the Internet. (6), (7), (8).