Service Oriented Architecture For GIS Applications

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1 The 12 th International Conference of International Association for Computer Methods and Advances in Geomechanics (IACMAG) 1-6 October, 2008 Goa, India Service Oriented Architecture For GIS Applications Pallavi S. Talegaonkar Dept. of Computer Engineering, D Y Patil COE, Pune, India Keywords: GIS, Web Service, Servlet/JSP, OGC, J2EE ABSTRACT : Geographic data which is immensely heterogeneous is increasingly becoming available on the Internet. For sharing and accessing this data GIS technology can be embraced within the context of an SOA using Web services. Open GIS Consortium has developed the web-based Geographic information and services accessible via internet through OGC consensus process. It was developed before SOAP emerged, so previously Web Map Server and Web Feature Server did not refer SOAP. As many of the design principles of distributed systems are crucial to apply to GIS services, GIS web services were designed to provide the hosted spatial data and GIS functionality to integrate the customized GIS applications to perform basic geo-processing tasks, such as address matching, map image display, and distance calculations without maintaining GIS tools or the associated geographical data. This implementation by Xiaolin Lu, in 2005 integrates web-service, Servlet/JSP functions and GIS APIS based on J2EE. Microsoft developed the MapPoint.NET Web Service for GIS mapping and location services that could be used for developing a broad range of location enhanced applications. Latest literature gives many implementations like E-GIS which follows SOA using web-services for integrating diverse repositories of spatial data and uses WMS and WFS of OGC. This paper discusses all key features and compares these different approaches for implementing web-service enabled GIS applications. 1 Introduction GIS systems are ubiquitous distributed systems, since geo-spatial information adheres to almost everything. In the strictest sense, it is a computer system capable of integrating, storing, editing, analyzing, sharing, and displaying geographically-referenced information. In a more generic sense, GIS is a tool that allows users to create interactive queries (user created searches), analyze the spatial information, edit data, maps, and present the results of all these operations to user. By the mid-1980s, geographic information system (GIS) software was heavily used in the natural resources and defense domains, especially within government agencies. The software was powerful for spatial analysis but people were not able to share geospatial data between systems efficiently. Web Services are the software components that can be accessed through the Internet in other applications.web services are frequently just Web APIs that can be accessed over a network, such as the Internet, and executed on a remote system hosting the requested services. GIS Web services are the software components that can provide the hosted spatial data and GIS functionalities and can be accessed and integrated to the practical customized GIS applications. Developers can apply the GIS Web services to perform geographical information processing and return the results to the customized applications without maintaining the basic GIS system or the geographical data. The service-oriented architecture is a very promising architecture for practical implementation of the next generation geographical information systems. The GIS web services have been thoroughly investigated in recent years (Xiaolin Lu 2005, Shengru 2004). There are a number of researches and developing projects of applying the web services to GIS system by several different companies and organizations. The Environmental systems Research Institute (ESRI) reported the ArcWeb Services that could include and integrate the GIS content and capabilities in the customized applications for sharing geographical information and data. Microsoft Mappoint.NET is a.net framework based hosted, programmable XML Web Service that allows application 1980

2 developers to integrate high quality maps, driving directions, distance calculations and proximity searches into there applications, business processes and web sites. This paper investigates all the previous implementations and latest techniques to construct distributed GIS applications based on Service Oriented Architecture. Also Web based GIS platform architecture is discussed along with two implementations. There are at least three characteristics of GIS services that make it difficult to design GIS web services with satisfactory performance. First, services provided by a GIS typically requires heavy CPU usage due to the complex computation involved in the underlying computational geometry. Second, GIS services often transmit large resulting data sets such as images. Third, the clients of GIS web services are often some complex software tools such as the CAD desktop applications. For scalable GIS, simply establishing communications between components is not sufficient. Performance should always be a central consideration in the design of GIS web service systems (Shengru 2004). 2 Overview of related work OGC developed the web-based geographic information and services accessible via the Internet through the OGC consensus process. Each service supports a certain GIS operation function that returns metadata describing the nature of the service, the methods to register Web Service, the addresses to access the service or to contact its provider, the type of data provided by the service, and so forth. The Environmental Systems Research Institute (ESRI) reported the ArcWeb Services that could include and integrate the GIS content and capabilities in the customized applications for sharing geographical information and data. Applications can access Web Services through Web protocols such as HTTP and XML, without concern for how each service is implemented. Microsoft developed the MapPoint.NET Web Service for GIS mapping and location services that could be used for developing a broad range of location enhanced applications, including wireless/mobility, customer relationship management, enterprise location services, and business intelligence (Microsoft, 2003). Although many researches have been devoted to apply the web services technology to GIS system with different kinds of GIS Web Services, few studies have been reported on the architecture design for building the Web service enabled GIS system platform. Investigation of the service-oriented architecture for building a distributed and web service enabled GIS platform has been done a lot. The related research aims to apply the web service framework into the GIS system design and implementation. The advantages of the architecture, functions, system integrations, and some key technical problems have also been discussed here. 2.1 Web Services Oriented Architecture Services are the software components that are well defined, self-contained, and does not depend on the context or state of other services (IBM, 2003). Web services essentially use XML to create a robust connection. The web services architecture has three roles: a provider, a requestor, and a broker. The provider creates the web service and makes it available to clients who want to use it. A requestor is a client application that consumes the web service. The broker, such as a service registry, provides a way for the provider and the requestor of a web service to interact. The provider, requestor, and broker interact with each other through the operations of publish, find, and bind. A provider informs the broker about the existence of the web service by using the broker's publish interface to make the service accessible to clients. The information published describes the service and specifies where the service is located. The requestor consults the broker to locate a published web service. With the information it gained from the broker about the web service, the requestor is able to bind, or invoke, the web service. The following figure illustrates a basic service-oriented architecture. Publish WSDL + UDDI Service Provider Bind Service Broker Find WSDL + UDDI Service Requester Figure 1. Web services oriented architecture The web services use SOAP (Simple Object Access Protocol), WSDL (Web Services Description Language), UDDI (Universal Description, Discovery and Integration), and WSIL (Web Services Inspection Language) to communicate. Web Services are published on the UDDI registry. A WSDL document defines the target service so the client knows what the service does. SOAP standardizes the way a Web service communicates with a client and allows programs written in different languages and on different platforms to communicate. SOAP works with standard Web protocols including XML, HTTP, and TCP/IP, as well as WSDL. 1981

3 Service Provider Service request Service Consumer Service response Figure 2. SOA Interaction between service provider and consumer Figure 2 shows the basic interaction of SOA. The request and subsequent response connections are defined in some way that is understandable to both the service consumer and service provider. Open GIS Consortium Web Services (OWS) OGC is an international industry consortium of more than 220 companies, government agencies and in order to allow interoperability between server and client software from multiple vendors, the request and response must be standardized. GIS Consortium is developing specifications to standardize the message interfaces (OGC, 2004). These include a. Web Map Service (WMS) for maps encoded as images; b. Web Feature Service (WFS) for geographic objects or vector data; c. Web Coverage Service (WCS) for continuous data; d. Sensor Collection Service (SCS) for live access to observations from sensors; e. Geography Markup Language (GML): XML components for encoding geographic objects for transport; Two standard web service techniques proposed by OGC, namely Web Map Service (WMS) and Web Feature Service (WFS) have been used for enabling a centralized access of spatial data of different format. WFS allow a client to retrieve geospatial data from multiple Web Feature Services. The OGC WMS is capable of creating and displaying maps, coming simultaneously from multiple sources, in standard image formats such as.svg,.png,.gif or.jpg. 2.2 OGC Web Map Service The OGC WMS specification offers a standard client-server interaction protocol that each map server implements as a common interface for accepting requests and returning responses [3]. The same client is able to access to all available OGC web map servers over the Internet. The client through the common interface accesses each map server. In a distributed OGC WMS, a WMS server can also run as a WMS Client that requests capabilities and maps from other WMS servers. An OGC web map server implements three functions : i. GetCapabilities, ii. GetMap and iii. GetFeatureInfo. The GetCapabilities function provides the client with a map server s service metadata, specifying its capabilities. The GetMap service specifies the map request parameters that enable the client to request an image map. Finally the GetFeatureInfo function allows the client to request more information about features at a specific location in the map. A structure of WMS mapping application is illustrated in figure 3 below. 1982

4 Figure 3. The system architecture of WMS mapping application The client application requests the information from the web map server. The map server retrieves from the database the appropriate layers of geo-feature data for the specified spatial domain and generates a map that can be viewed directly in a graphical web browser or other pictorial software. The client and web map server interact using Hypertext Transfer Protocol. OGC WMS is an interoperable web mapping system. It provides common interfaces to connect with the client application and dynamically process geo-referenced data such as geographic maps and features coded using Geography Markup Language (GML) documents. The OGC Web Map Service specification defines a set of functions that clients may use to interact with WMS providers (servers). Any client making requests that conform to the specification can interact with any server that implements the WMS service. In effect, this creates an interoperable, distributed web mapping system. Here a web service based approach is used for the integration architecture. The data repositories are available on the web as services with some well interface. It is based on XML technology and a client can access any data repository having data in any format located on any platform if it only knows how to communicate with service provider. The goal is to provide unified access to data from heterogeneous data providers. Any client (user) can submit its query to a geospatial server. The server, on the other hand, will retrieve the data from the multiple sources and return the result to the client. This will help in realizing interoperability between the heterogeneous data repositories. 3 Service Oriented Architecture Design for Distributed GIS Platform The goal of the Service Oriented Distributed GIS platform is to provide both the dynamic GIS service components for publication of vector and raster maps to Internet and interactive viewing on web browsers. It supports the complex rendering, navigation and allows working with multiple layers, thematic maps, hyper linked features and attribute data. The fundamental GIS platform is based on the Client/Server architecture. The server spreads vector maps to client. The map features are stored on a SQL database according OGC SFS and WMS that can be used as raster maps source. The GIS data interface supports the ArcView shape files and MapInfo MIF files. The server side is constructed based on J2EE architecture. 3.1 GIS Web services design principles GIS Web Services are discoverable, self-describing software components. UDDI is an open standard with broad industry support standard. When an implemented GIS Web Service exposed in any Web Services portal, it can be discovered in any Web Services portal. Once a GIS Web Service is discovered, the developer can begin using it immediately. All they need is the full URL path to the services WSDL. Each method, parameter, property, and return value of the service is described in a standard way, allowing modern development tools to immediately allow access to the exposed functionality. GIS Web Services conceal complexity. Web Services embed its complex data processing within itself in server side. Client side application developer makes use of Web Services through standard interface which described in Web Services WSDL, therefore the application developer don t need dealing with Web Services internal process. The following principles are considered in the design for the service oriented distributed GIS platform. Web GIS platform should provide a variety of interfaces for integration and interoperability with business and GIS applications GIS Web services: Web GIS platform should support the standard enterprise application server technologies to build web services 1983

5 with embedded spatial services, software components and APIs to easily embed spatial capabilities in business applications built using standard technologies and architectures Web Mapping Services (WMS): WMS can display map layers from other GIS applications, and allow other applications to display map layers from Web GIS platform OpenGIS Consortium interoperability services and standards: The Web GIS platform should be implemented with the OpenGIS interoperability standards: Geography Markup Language (GML): GML is a common XML-based file format for exchanging spatial information and attributes. The Web GIS platform should support the GML standards. Common database environment: Specifications on spatial entities and the space / time reference systems have been provided by the OpenGIS Consortium. 4 GIS platform architecture design The GIS platform architecture is designed as a multi-layer architecture that integrated the web service, Servlet/JSP functions and GIS APIs based on the framework of J2EE infrastructure. The GIS system can be accessed by lots of different computers in network with different kinds of operating system. It is a distributed, platform independent system architecture. The data are stored and managed with EJB. The distributed systems enable the databases and services in the same or different computers. The figure 3 shows the Web GIS platform server environment. The Web GIS platform Server architecture is consisted of three layers: User Interface Layer, Application Server Layer and Database Layer. 1) Application Server Layer : In the application server layer, the GIS web services, Servlet/JSP interface, OGC services which include GML and WMS map service, and basic system application service is deployed in the J2EE server container. The GIS function such as the zooming out and in, viewing, panning and finding will be designed as an function session bean that can be accessed by the GIS web service, Servlet/JSP and other Application interfaces. The application server layer is built as a J2EE application, with several EJB modules, to provide server-centric spatial functions to applications. Key components of the server that implemented as EJBs are: Web GIS services, Geo-spatial functions, such as the viewing, layer selection, editing, querying, and analysis Data Source Management. The J2EE based Web GIS server layer is shown in the figure 4. 2) User Interface : Web GIS platform provides a number of user interface components: Web service client, GIS java Applet and any other web service enabled applications. The mobile and PDA that support the web service standards interface could get the map and geo-referenced data through the GIS web service interface. The web browser based clients could communicate with the Web GIS service through the GIS web service, Servlet/JSP and OGC service. The clients perform URL requests to Map Service and obtain maps rendered in a pictorial format such as GIF or JPEG. A GIS Java Applet is another user interface tool that can be used to retrieve and handle the vector and raster data. Applet enables spatial viewing, querying, and richer editing capabilities to be easily embedded in desktop and web applications. 1984

6 Figure 4. Service Oriented Architecture of Web GIS Platform 3) Database Layer : The GIS data are stored and managed with the distributed systems architecture that enables the GIS data, databases and services in the same or different computers. The GIS platform should support following GIS data format : 1. Vector data and Raster data ESRI shape files: ESRI shape files can contain points, multipoint, polylines and polygons objects. The attribute data is stored in dbase. 2. MapInfo MIF: MapInfo MIF is stored in pair with DBF file not with MID. MIF contains region, poly-line, multiple line and point. All objects are the same type. 3. SQL database: It can be any SQL server with JDBC driver. 4. GIF and JPG image files. 5. OpenGIS Web Map Service According to the service-oriented architecture proposed in above section, design and implementation of a prototype of the service enabled GIS platform has been tested. The GIS platform architecture is designed as a multi-layer architecture that integrated the web service, Servlet /JSP functions and GIS APIs based on the framework of J2EE infrastructure. It is a distributed, platform independent system architecture that can be accessed by lots of different computers in network with different kinds of operating system. The web service framework was applied into the GIS system design. GIS web services can provide hosted spatial data and GIS functionality and integrate to the customized GIS applications to perform basic geo-processing tasks, such as address matching, map image display, and routing, without maintaining GIS tools or the associated geographical data. The GIS platform has been used to build up a SARS prevention GIS application system. GIS Web service was used to get and show the geographical information. The application integrated the GIS Services and SARS information Service into a java applet in browser to report the most recent SARS case information. Since the requirement of the practical GIS application in different application domains and fields are quite complicated, integration of a general GIS web-service into user customized application is difficult. So work on common GIS web services is the next step. ArcWeb Services by ESRI and OGC are doing extensive research in this area. 1985

7 5 E-GIS organization wide approach to GIS implementation 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 (Open Geospatial Consortium) standards (OGC, 2007). Enterprise geographic information system (E-GIS) is an organization-wide approach to GIS implementation, operation, and management. E-GIS can also be defined as an effort to design integrated geospatial management techniques to serve a complex institution(ghosh and Manoj, 2007). 5.1 Geospatial Domain The open and distributed GI domain opens a wide range of possibilities for acquiring, processing and analysing geographic information without the need of GIS expert knowledge. In an environment where services are previously unknown, a service that is appropriate for answering a given question from among a large number of available services has to be discovered first. Service discovery is a crucial task that will become even more important with the emerging Semantic Geospatial Web. OGC WFS provides a set of protocols to provide standardized service interfaces for the geospatial data sources. Through these services distributed geospatial data can be accessed and processed across administrative and organizational boundaries. As the data sources are less coupled to the integrated system, they can be created and managed locally, which leads to increasing uality and efficiency. The integrated system can be extended to include new services and/or data sets. 5.2 Integrating Geospatial Repositories The issue of how to capture data from several highly heterogeneous spatial data sources and integrate them for analysis becomes important for the web-based GIS application. The development of web technologies and Internet provide a way to quickly access various geodatabases. The internet has become immensely valuable and been recognized as an important means of quickly disseminate information and acquire data from spatial data repositories (David 1998, Peng 2003, Peng 2004). This project is an integrated Java enterprise based implementation of the 1.0 Web Feature Server(WFS) (OGC 2002) and Web Map Service(WMS) OGC 2004 specification from Open Geospatial Consortium. The objective is to enable greater geographic interoperability by reinforcing OGC standards and other web standards and lowring the barriers to entry for geographic data providesr. Request to the WFS server provides the feature datain GML format. On the other hand WMS request to WMS server serves the data by graphically rendering it i.e. in Map Format. The data can be integrated 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 the3 WFS). The primary goals are : 1) Standard compliance : Adhere to open standards and support as many relevant geographic standards as possible. 2) Data format support : In order to make the server useful, it must help translate the current diversity in geographic data formats into a single format (GML). 3) Ease of Use : Easy to configure and run with few technical resources. 4) Efficiency : As efficient as possible while achieving other goals. 1986

8 WFS Request / Response WMS Request/Response Figure 5. Service Driven access of data from Spatial Database The interface between spatial database and OGC web services is shown in the above figure.wfs 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. 6 Conclusion In this paper I have analysed different methods and implementations for SOA based implementation of GiIS applications. Service based technology based on SOA architecture is the emerging trend used in almost every field now. Geographic data which is increasingly available now on Internet should be easily shared and accessed by users. GIS data is immensely heterogeneous, being available in various formats and stored in diverse media. So two different implementations of accessing this data have been discussed here. The first approach is the multi-layer GIS platform architecture that integrated the web-service, servlet-jsp functions and GIS APIs based on J2EE architecture. The second approach uses SOA architecture for integration of geospatial data repositories and also discusses query processing and domain specific computational capabilities. In this inter-organizational sharing of spatial data can be achieved with web-service based WMS/WFS. The further work is for designing a web-service client which invokes the services of server in specified format. 7 References Manoj Paul, S. K. Ghosh A Service driven approach for Integration of Heterogeneous Geospatial Data repositories, Indian Institute of Technology, Kharagpur, India- GIs Development proceedings, the Global Geospatial Magazine August Mircosoft. MapPoint.NET Demos. Available at Open GIS Consortium Inc, Web Map Service Implementation Specification Open GIS project document: OGC r2, June OGC, 2004., Web Map Service, Version 1.3. [ Shengru Tu, Maik Flanagin, Ying Wu, Mahdi Abdelguerfi, Eric Normand, Venkata Mahadevan, Jay J. Ratcliff and Kevin Shaw, Design Strategies to Improve Performance of GIS Web Services, In: International Conference on Information Technology: Coding and Computing (ITCC'04), Volume 2, Las Vegas, Nevada, USA, April 5-7, 2004, pp Xiaolin Lu - College of Information Technology, Zhejiang University of Finance & Economics Hangzhou, Zhejiang, China in : Proceedings of the 2005 IEEE International Conference on Services Computing (SCC 05) /05 $ IEEE. ESRI, An Overview of ArcWeb Services, Available at pdf. July IBM, Web Services architecture overview, Available at ibm.com/developerworks/ webservices/library/ w-ovr/