Abstract
Web Feature Service (WFS) is a protocol for accessing geospatial data stores such as databases and Shapefiles over the Web. However, WFS does not provide direct access to data distributed in multiple servers. In addition, WFS features extracted from their original sources are not convenient for user access due to the lack of connection to high-level concepts. Users are facing the choices of either querying each WFS server first and then integrating the results, or converting the data from all WFS servers to a more expressive format such as RDF (Resource Description Framework) and then querying the integrated data. The first choice requires additional programming while the second choice is not practical for large or frequently updated datasets. The new contribution of this paper is that we propose a novel adaptive and optimized RDF query interface to overcome the aforementioned limitation. Specifically, in this paper, we propose a novel algorithm to query and synthesize distributed WFS data through an RDF query interface, where users can specify data requests to multiple WFS servers using a single RDF query. Users can also define a simple configuration to associate WFS feature types, attributes, and values with RDF classes, properties, and values so that user queries can be written using a more uniform and informative vocabulary. The algorithm translates each RDF query written in SPARQL-like syntax to multiple WFS GetFeature requests, and then converts and integrates the multiple WFS results to get the answers to the original query. The generated GetFeature requests are sent asynchronously and simultaneously to WFS servers to take advantage of the server parallelism. The results of each GetFeature request are cached to improve query response time for subsequent queries that involve one or more of the cached requests. A JavaScript-based prototype is implemented and experimental results show that the query response time can be greatly reduced through fine-grained caching.
Highlights
Web Feature Service (WFS) [1,2] is a Web-based protocol that supports feature-level access to geospatial data stores such as spatial databases, Shapefiles, and GML (Geography Markup Language) files
If there are a large number of WFS feature types, it might be better to use an automatic matching algorithm to generate mapping candidates between WFS feature types and Resource Description Framework (RDF) classes and manually finalize the mapping rules based on the generated candidates
We present an algorithm to convert RDF queries to WFS requests so that users can query distributed WFS features as if they were RDF instances
Summary
Web Feature Service (WFS) [1,2] is a Web-based protocol that supports feature-level access to geospatial data stores such as spatial databases, Shapefiles, and GML (Geography Markup Language) files. WFS services have been implemented in systems such as GeoServer [3] and MapServer [4] Web interfaces such as those based on OpenLayers library [5] have been used to retrieve geospatial objects remotely over HTTP protocols and to display the results on a browser. The August Tropical Storm Irene and the October Nor‘easter in 2011 exposed the deficiency in geospatial data sharing in the response and management of the storm disasters Under these situations, rapid prototyping of Web-based applications is necessary to allow disaster responders and managers to share and update timely and accurate geospatial data over the network. Directly using WFS for this purpose has two drawbacks
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