WMS and GML based interoperable web mapping system

Recently the World Wide Web has become a popular vehicle for information distribution and web based geographic information systems (GIS) are rapidly evolving and adapting to these new environments. The main hindrance for building true interoperable distributed geographic information systems is the lack of any standard exchange mechanism between the diverse GISes connected over the web. Recent efforts by the OpenGIS Consortium have resulted in several specifications to alleviate these problems. Web Map Sever (WMS) and Geographic Markup Language (GML) are such standards for developing interoperable web based Geographic Information Systems (Web-GIS). GML is an XML (eXtensible Markup Language) encoding for the transport and storage of geographic information, including both geometry and properties of geographic features. In this paper we describe a WMS compliant map server and GML based client. This integrated system leads to a true interoparable Web-GIS. GML based client for the first time offers client side query processing capabilities and at the same time provides several challenges. The parsing techniques have performance considerations since the size of GML documents is generally huge and often the queries result in multiple passes over these documents. In this study we also evaluated the two well known parsing approaches - simple API for XML (SAX) and the document object model (DOM) for single and multiple passes. Our study shows that SAX performs better than DOM for single pass; thus for simple applications like visualization, subsetting, the SAX model is superior. However, for intensive applications involving queries requiring multiple passes over documents or integration of multiple documents in a distributed environment, DOM based parsing offers a better solution.