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A Route to Societal
GIS ? - Geospatial Web Services Web Services standards – openness and interoperability This is feasible only through focus on standardising the messaging between services as opposed to standardising the application providing or consuming the service. Regardless of the kind of program or software executing the service, as long as the description of how to access it, input and output data formats all conform to a published standard, the application will be able to communicate with others. Web services therefore depend on a number of developing Web protocols including, eXtensible Markup Language (XML), Simple Object Access Protocol (SOAP), Universal Description Discovery and Integration (UDDI) and Web Services Description Language (WSDL). The World Wide Web Consortium’s (W3C) (http://www.w3.org/) XML protocol has been adopted as the de-facto standard for describing data transferred in Web service applications. Now widely established throughout Web computing, it owes its success to its flexibility – defining a syntax with which data descriptions can be defined rather than attempting to describe all forms of data itself. In this way XML has been able to be adopted by a variety of different vertical markets each agreeing their XML compliant definitions or schema. Thus, for spatial features, the Open GIS Consortium (OGC) (http://www.opengis.org/) has led the development of Geographic Markup Language (GML), an XML schema designed to provide a cross-platform description for spatial data. Since its launch in March 2001, this effort has been gaining wide support within the GIS community. The standard is still evolving and work within the OGC by leading GIS and IT vendors such as ESRI, Intergraph, Oracle, Sun Microsystems, and key users, is continuing, with the goal of enhancing this standard to allow for complex commands and very large datasets. OGC is working on similar Web map server specifications. XML also forms the basis of SOAP and WSDL. SOAP is designed as a standard envelope for delivering method invocations – basically a means of wrapping an XML document so that the recipient knows what to do with it on receipt. SOAP enables an XML statement to be sent over HTTP to a Web service and provides a clear mapping between parameters and function calls. WSDL is another W3C standard which defines a template to be used for describing a service. This tells the client what the service offers and in detail how to create and interpret both request and response. It defines the methods available, what their parameters are, parameter types and the nature of the output generated. WSDL is used by service providers to publish information on their service. UDDI represents a standard Web based directory of services – in effect a yellow pages of Web services. Though it is not necessarily a requirement to publish WSDL documents to UDDI, doing so avoids the need to hardcode service location and parameter details in to client applications giving them greater flexibility in the event of a particular service being temporarily out of action. This concentration on standardizing the message rather than application at either end enables Web services to offer robust inter-operability between different platforms and applications – a key component of Societal GIS. GIS Web Services in Practice Web Services appear at least in theory to be able to provide many of the characteristics demanded of Societal GIS – open, interoperable, encouraging multi-participation, robust availability and capable of easy, rapid organic growth. Is this converted into practice? Though a relatively new approach, there are increasing number examples where Web services are being deployed to create what may be described as Societal GIS. Spatial Data One-Stop – Joining up Spatial Resources Work on Spatial Data Infrastructures (SDI) whether at a national or global scale has been going on for a number of years. SDI ensure an awareness and compatibility of data between organisations that are essential prerequisites for Societal GIS. In the United States, the Federal Geographic Data Committee (FGDC) has been working on the development of the National Spatial Data Infrastructure (NSDI) in cooperation with organizations from State, local and tribal governments, the academic community, and the private sector. The NSDI encompasses policies, standards, and procedures for organizations to cooperatively produce and share geographic data. A Web Service based portal, www.geodata.gov, launched on 30 June 2003 is now providing a gateway, a one-stop shop, for accessing the data, procedures, applications and projects that have been brought together by the NSDI. Built by ESRI, Inc. within just eight weeks the Geodata portal is designed to be open and interoperable with virtually any GIS data set and service. It incorporates standards from OGC, ISO, FGDC as well as Web and computing industry. The portal provides a single point of access to services hosted by hundreds of different participants from across the spectrum of government, national and international organisations and the academic and private sector. Not only does it simplify the search for data, it provides rapid access to applications, projects, metadata, viewing engines, best practice notes and projects providing a central open geospatial resource.  Figure 3: Geospatial One-Stop providing access to USA's spatial data The resources accessible through the Geodata One-Stop portal are vast. The aim is to lead users to data that they are searching for within only two or three clicks of the mouse. Information can be access in a number of ways
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