Towards a Geoprocessing Web

As Web services technology has matured in recent years, an increasing amount of geospatial content and processing capabilities are available online as Web services. These Web Services enable interoperable, distributed, and collaborative geoprocessing to significantly enhance the abilities of users to collect, analyze and derive geospatial data, information, and knowledge over the network. A Web-based distributed geospatial computing and large networks of collaborating applications is emerging as the next step in the evolution of geoprocessing. The Geoprocessing Web is changing the way in which geoscience applications and systems are designed, developed and used. In this special issue, we collect a number of research and application papers to present the current research on theoretic frameworks and practical implementations in the Geoprocessing Web, and identify related challenges and open issues. What are the distinguishing characteristics of the Geoprocessing Web? What are the achievements and challenges of the Geoprocessing Web with respect to data, service, workflows and semantics? The paper by Zhao et al., tackles these questions, and provides a comprehensive overview about the state-of-the-art architecture and technologies, and the most recent developments in the Geoprocessing Web. Interoperability is achieved by using standards. The Open Geospatial Consortium (OGC) has developed the Web Processing Service (WPS) specification that defines common service interfaces and message encodings for standard Web-based geoprocessing. The paper by Lopez-Pellicer et al., discusses the use of search engines and focused crawlers for checking the availability of the OGC WPS, and provides quantitative data about the scalability of the Geoprocessing Web. The interoperable OGC WPS can be used as the mediation allowing one to seamlessly execute a geoprocessing job on different computing platforms ranging from a standalone GIS server up to computer clusters and large Grid infrastructures. The paper by Giuliani et al., proposes an extension of OGC WPS for mediating different geospatial and Grid software packages. The service-oriented workflow is essential for complex geospatial applications and knowledge discovery over the Web. Service composition concerns with how to discover, coordinate, and integrate a set of component services. The paper by Li et al., proposes a QoS-aware game theory approach to geoprocessing service composition for concurrent tasks. In his paper, a noncooperative game-based mathematical model, which is related to the competitive relationships between tasks, is used to build a best response function to maintain the workflow optimization. As opposed to the commonly used process-centric composition model, the paper by Jesus et al., presents how to use a newly