A Service Oriented Architecture for Enterprise-GIS Manoj Paul School of Information Technology Indian Institute of Technology , Kharagpur, India mpaul@sit.iitkgp.ernet.in  S.K.Ghosh School of Information Technology Indian Institute of Technology , Kharagpur, India skg@sit.iitkgp.ernet.in S.C.De Sarkar School of Information Technology Indian Institute of Technology , Kharagpur, India scd@cse.iitkgp.ernet.in P.S.Acharya Department Science and Technology Govt. of India New Delhi, India psa@nic.in Abstract: In government and other agencies, GIS is often developed with diverse departments relying on a mix of software and information systems. Each department uses its individual system to increase efficiency, but sharing data and applications across the enterprise is a near impossibility. An increasing number of institutions are challenged with implementing robust geographic information system (GIS) capabilities for a large number of individuals through information sharing and interconnected networks. Enterprise geographic information system (E-GIS) is an organization-wide approach to GIS implementation, operation, and management. An E-GIS provides access to shared geospatial information and analysis resources for a large number of concurrent users located in different parts of an institution. We have followed a service-oriented architecture using web services for integrating diverse repositories of spatial data. OGC Web Map Service (WMS) and Web Feature Service (WFS) have been used for enabling a centralized access of spatial data of different formats. 1 INTRODUCTION In government and other agencies, Geographic Information System (GIS) is often developed with diverse departments relying on a mix of software and information systems. Each department uses its individual system to increase efficiency, but sharing data and applications across the enterprise is a near impossibility. An increasing number of institutions are challenged with implementing robust geographic information system (GIS) capabilities for a large number of individuals through information sharing and interconnected networks. In the past, numerous technological roadblocks hampered the successful implementation of enterprise-wide GIS system (E-GIS). With the advent of high-speed networks; increasingly fast computers; intelligent, spatial-data serving technologies; improved data architecture; and advances in GIS software; the newest challenge involves integration of the various technological and institutional components, addressing the interoperability problem through OGC standards. Enterprise geographic information system (E-GIS) is an organization-wide approach to GIS implementation, operation, and management. An E-GIS provides access to shared geospatial information and analysis resources for a large number of concurrent users located in different parts of an institution. EGIS can also be defined as an effort to design integrated geospatial management techniques to serve a complex institution. In this paper we have followed a service-oriented architecture (SOA) using Web Services for integrating diverse repositories of spatial data. Two standard Web Service techniques proposed by OGC - Web Map Service (WMS) (OGC, 2004) and Web Feature Service (WFS) (OGC, 2002) have been used for enabling a centralized access of spatial data of different formats. WFS allows a client to retrieve geospatial data from multiple Web Feature Services. The OGC WMS is capable of creating and displaying maps that come simultaneously from multiple sources, in standard image formats such as .svg, .png, .gif or .jpg. The rest of the paper is organized as follows: Section 2 provides a detailed description of the technologies followed, the architecture of the system is described in section 3, finally we conclude in section 4. 2 INTEGRATING GIS SOURCES The issue of how to capture data from several highly heterogeneous spatial data sources and integrate them for analysis becomes important for web-based GIS applications. The development of World Wide Web (WWW) and Internet provides a way to quickly access various geo-databases. The Internet has become immensely valuable and been recognized as an important means of quickly disseminating information and acquiring data from several spatial data repositories (David, 1998; Peng, 2003; Peng, 2004). For providing a centralized access of data from multiple data sources each individual institution is required to register its data in a central registry, which enables maintaining a catalogue of data. The catalogue should contain information about data type, feature information etc. Upon request, data is searched in the catalogue and request for the corresponding data can be sent to the feature request module. Whatever be the input data format, the output data is to be sent in the Geography Mark-up Language (GML) (OGC, 2003) format for ensuring interoperability. This project is an integrated Java implementation of the 1.0 Web Feature Service (WFS) (OGC 2002) and 1.1.1 Web Map Service (WMS) (OGC 2004) specification from the Open geospatial Consortium (OGC). The objective is to enable greater geographic interoperability by reinforcing OGC standards and other web standards and lowering the barriers to entry for geographic data providers. Request to the WFS server provides the feature data in GML format. On the other hand a WMS request to the WMS server serves the data by graphically rendering it i.e. in map format. The work presented in this paper can integrate data in flat file format (Shape format and GML format) and relational database format (Oracle Spatial). With this approach data can be published as maps/images (using the WMS), as actual data (using the WFS). The main focus is ease of use and support for open standards, in order to enable anyone to quickly share their geospatial information in an interoperable way. With the recent research on adopting Web Services for Web-based GIS application, the issue of sharing spatial data has taken a new dimension. With Web Services it becomes possible for applications to acquire and integrate spatial data from heterogeneous sources in real time over the web. OGC web services provide a vendor-neutral interoperable framework for web-based discovery, access, integration, analysis and visualization of multiple online geospatial data sources. Web Feature Service (WFS) and Web map Service (WMS) - the two important web service standards proposed by OGC - have been adopted in this project. 2.1 Web Feature Service Web Feature Service is one of the GIS web service interoperable specifications defined by OGC (OGC, 2002). It is the most powerful data service of OGC Web Services. Web Feature Service allows a client to retrieve geospatial data from multiple geospatial data servers. It also supports INSERT, UPDATE, DELETE, QUERY and DISCOVERY operations on geographic features using HTTP as the distributed computing platform. WFS defines three main operations: GetCapabilities operation describes capabilities of the web feature service using XML, it indicates which feature types it can service and what operations are supported on each feature type. DescribeFeatureType operation describes the structure of any feature type it can serve. GetFeature operation services a request to retrieve feature instances. In addition, the client should be able to specify which feature properties to fetch and should be able to constrain the query spatially and non-spatially. 2.2 Web Map Service The OGC WMS is capable of creating and displaying maps that come simultaneously from multiple sources, in standard image formats such as Scalable Vector Graphics (SVG), Portable Network Graphics (PNG), Graphics Interchange Format (GIF) or Joint Photographic Expert Group (JPEG) (OGC, 2004). It provides 3 operations: GetCapabilities allows a client to instruct a server to provide its mapping content and processing capabilities and return service-level metadata; GetMap enables a client to instruct multiple servers to independently craft "map layers" that have identical spatial reference system, size, scale, and pixel geometry. The client can then display these overlays in a specified order and transparency such that the information from several sources is rendered for immediate human understanding and use; GetFeatureInfo enables a user to click on a pixel to inquire about the schema and metadata values of the feature(s) represented there. 3 Architecture of the system The overall architecture of the system is shown in figure 1. Integration of the data repositories is realized with the help of standard web service technology (WFS, WMS) specified by OGC. At core of the system is a central registry, which holds the information of all the data repositories that a user can avail data from. All the data providers need to register their data at the central registry. The registry registers the data in a catalogue with the information of the dataset, e.g. type of the data (shapefile, gml file), feature name (to identify a feature uniquely and subsequently accessing the feature data with this name), namespace of data (for semantic access), spatial reference system (SRS) etc in a catalogue.xml file. Sample entry in the file is as follows   Figure 1: Architecture of the system Data can also be on standard relational database management system like Oracle, PostGIS database. Oracle is preferred for spatial data storage due to its spatial data storage capability. For each feature one style file is associated which is used to format the display of the spatial data. Client can avail of the actual data by requesting a feature through getFeature request. A request can be sent to the server as a GET or a POST. An example of a getFeature request is as follows http://localhost:8080/geoserver/wfs? request=getfeature& service=wfs& version=1.0.0& typename=roads The different parts of the request are:
http://localhost:8080/geoserver/wms?bbox=-0.0014,-0.0024,0.0042,0.0018& styles=cite_forests&Format=image/gif&request=GetMap& layers=cite:Forests&width=650&height=450&srs=EPSG:4326 The output of the request is shown in figure 2a. Data can also be requested from multiple data repositories. Since data from different sources are available as features, multiple features can be specified in the layers to obtain multiple feature data. The data is displayed to the requester in overlayed form with proper positioning taken care by the bbox and SRS attributes of the getMap request. All the features should have the same SRS for overlaying. Figure 2b shows data requested from multiple sources and the corresponding output. The request format is same except that the layer portion where multiple features have been specified is as follows http://localhost:8080/geoserver/wms?bbox=-0.0014,-.0024,0.0042,0.0018& styles=cite_forests&Format=image/gif&request=GetMap& layers=Forests, road, river, house, & width=650& height=450& srs=EPSG:4326  Figure 2a: getMap request from single source Figure 2b: getMap request from multiple sources 4 CONCLUSION Geographic data is increasingly becoming available on the Internet, allowing a large number of users to share and access the rich databases that are currently being maintained in several organizations. However, GIS data is immensely heterogeneous, being available in various formats and stored in diverse media (flat files, relational database). In this paper we have discussed SOA architecture for the Enterprise-wide GIS (EGIS) system. The problem is not only to integrate these heterogeneous data sources, but also the query processing and domain specific computational capabilities supported by these sources, which makes GIS integration a real challenge. As the spatial data repositories may be located in several organizations, inter-organization sharing of spatial data can be achieved with web service based WMS/WFS. The Web Service based integration technique for spatial data repositories has been addressed in the paper with a case study. Data stored as flat files or in relational DBMS has been integrated for interoperable access. Designing a Web Service client, which can invoke the services of the server by sending request in specified format, can do further enhancement. ACKNOWLEDGEMENT This work has been partially funded by NRDMS, Department of Science & Technology, New Delhi. REFERENCES
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