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Online network analysis from heterogeneous datasets - Case study in London train network
4.5 Application interface An application was developed using Java applet technology. A Java applet is an application that can run on a web browser whilst the applet itself resides on a server. A number of Java classes were developed to support a customisation of the application system. Several tools of basic GIS rendering functions (e.g. zoom/pan) were developed. 5. The case study of London train network The application of London train network was developed to find the shortest path for a journey between two stations. In this case, the weight for the shortest path is the distance of the geometry which is derived from the geometry of network features. An additional linear network feature called "alink" was set for a connection line between network features that can be interchanged at interchange stations. The rules of feature connectivity for London train network are defined as follows. 
The semantics of network features are coded in the semantic schema as follows. 
When the application starts up, it sends the request of the project of London train network to the integration engine servlet. This engine will read the project document. It then opens connections to data servers and retrieves all data defined in the project. It also creates a network family object which contains the rules of feature connectivity. Finally, all feature objects with the network family object are sent back to the application at the client side. Once the application gets all required objects, it will clean geometry and build the network topology. After building the network topology, it is ready to perform the shortest path analysis function. The application shows the map of the London train network as a background. It provides a list of station for departure and destination stations and a shortest path function. The result of shortest path will be shown using a high-light graphic. After finding a shortest path, a report is generated to list a route and the stations in the shortest path result. 
Figure 4. The application system of the London train network application 
Figure 4. The report of the shortest path 6. Conclusion This paper has reported the development of the software system that is able to combine data from different data sources through the web and conduct network analysis from those datasets. The advantages of using geospatial interoperable standards and specifications (e.g. GML) have shown the important role interoperability standards have, not only for this implementation but also to the GI community at large. Using GML means that we do not worry about the formats of datasets. Using a web based approach for sharing data maintains data ownership at source but ensures the ability to share that data through various protocols. The system developed shows the possibilities for developing complex analytical GIS applications without regard for proprietary data formats using interoperable standards, interfaces and formats. Reference:
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