A Comparative Assessment of Giservices Architectures


Wilaiporn Sriphaisal, Arun K. Pujari
Department of Computer and Information Sciences,
University of Hyderabad,
Hyderabad 500046, Andhra Pradesh, India
mc03pc06@uohyd.ernet.in, akpcs@uohyd.ernet.in


Abstract
The development of GIS technology has evolved from mainframe GIS to desktop GIS to distributed GIS. The traditional GIS, referring to mainframe GIS and desktop GIS, are called GISystems. Distributed GIS is referred as GIServices which includes wired Internet GIS and wireless mobile GIS. The major difference between them is that GISystems work on wired, while GIServices work through both wired and wireless networks. Today technologies of interoperability standards give the ability of a system or components of a system to provide geographic information portability and inter-application. The user who cannot support immense budget for building their own GISystems can access, exchange and process geographic information from different providers. Getting clearance maps and data from ready-to-use mapping providers may not difficult but time consuming. GIServices are effective tools for decreasing both budget and processing time for the end user. Numerous users from anywhere are able to access, exchange, and process geographic information from various providers at any time.

The present work is a study of recent GIServices Architectures. In this paper, we discuss the strengths and weaknesses of these architectures. Besides the general aspects of the architecture, we concentrate to specific aspects namely, real-time, on-the-fly geoprocessing. It is interesting to note that many of major GIServices architectures have not given proper emphasis on on-the-fly geoprocessing. In this paper, we try to justify that this is one of the most desirable features of any GIServices. The objective is to arrive at a new architecture that can enhance real-time and on-the-fly characteristics.

1. Introduction
A survey of the GIS Web services available on the Internet shows that most of those sites are static in the sense that the Web pages are manually prepared and updated. Users frequently have trouble of getting user-defined maps and/or geographic information because they get bogged down in the real-time and on-the-fly geoprocessing. GIS Web Services, so called GIServices, are software components that can be accessed through the World Wide Web (WWW) and used by other applications [12]. GIServices provide spatial data or functionality on the WWW. They make it possible for users to access GIS data and functionality through the Web and to integrate them with their own systems and applications without the need to develop on host specific GIS tools and data sets themselves.

2. Background

2.1 Types of GIS architecture
The development of GIS technology has evolved from traditional GISystems to client/server GISystems to distributed GIServices [8]. The mainframe GIS and desktop GIS are traditionally called GISystems. Traditional GISystems are closed, centralized systems that incorporate interfaces, programs, and data. Each system is platform dependent and application dependent. Every element is embedded inside traditional GISystems and cannot be separated from the rest of the architecture. Traditional GISystems works on stand alone system.

Client/server GISystems are based on generic client/server architecture in a wired network design. The client-side components are separated from server-side components and usually platform dependent. Client/server architecture allows distributed clients to access a server remotely by using distributed computing techniques such as Remote Procedure Calls (RPC) or database connectivity techniques such as Open Database Connectivity (ODBC). Each client component can access only one specified server at one time. Different geographic information servers come with different client/server connection frameworks which cannot be shared.

Distributed GIServices enable users to manipulate GIS data and maps interactively over the wired Internet or wireless telecommunication networks. It is not necessarily required the user to install GIS programs on the user’s desktop. Distributed GIServices can interact with heterogeneous systems and platforms without the constraints of traditional client/server relationships. There is no difference between a client and a server. Every GIS node embeds GIS programs and geodata. Each GIS node can become a client or a server based on the task at hand. A client is defined as the requester of a service in a network while a server provides a service. There are two categories of distributed GIS: Internet GIS and mobile GIS. The major difference between them is that Internet GIS works on the wired Internet networks and the client is usually a desktop computer, while mobile GIS works through the wireless telecommunication networks and the client may be a laptop computer, a Personal Digital Assistant (PDA), or a mobile phone.

2.2 Evolutions of distributed GIS
The evolution of distributed GIS is following the development of computer technologies and telecommunication networks. It started with static map publishing and evolved to static Web mapping, to interactive Web mapping and to the distributed GIServices [8]. Static Map Publishing distributes maps on the Web page as static map images in graphic formats like Portable Document Format (PDF), Graphic Interchange Format (GIF), or Joint Photographic Experts Group (JPEG). The ready-made maps on the Web are usually part of HyperText Mark up Language (HTML) document. Users cannot interact with the maps or change their display format in any way.

Static Web mapping involves the use of HTML forms and the Common Gateway Interface (CGI) to link the user input on the Web browser with GIS or mapping programs on the servers. Users make requests from the Web browser using customized HTML forms. Then the request is sent to the CGI through a HyperText Transfer Protocol (HTTP) server to invoke GIS or mapping engines. The GIS or mapping engines create the map based on the user’s request and generate an image map. The image is sent via HTTP back to the user on the Web browser. Users cannot define or draw anything on the image maps because the HTTP form is text based and allows limited user input.

Interactive Web mapping adds scripts like Dynamic HTML (DHTML) and/or client-side applications like plug-ins, ActiveX control, and Java applets to the Web client side. Some user queries can be processed on the client side without sending requests to the servers. This approach requires HTTP connections and the Web servers to mediate between software objects running on the client and the servers which store these objects. Interactive Web mapping does not meet the requirement of distributed GIServices completely. Client-side application as mentioned above are design essentially fro graphic display of maps rather than truly providing GIS operations and analysis. Interactive Web mapping give very limited functionality that does not offer much interactivity and flexibility for complicated GIS modeling and processing.

Distributed GIServices refers to a specific software framework. GIS components on the client side can directly communicate with other GIS components on the server without going through the CGI middleware and an HTTP server. Distributed GIServices rely on the communication between Common Object Request Broker Architecture (CORBA)/ Java ORB or Microsoft Simple Object Access Protocol (SOAP) on the client side.



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