JAVA-Servlets approach
Servlets are web server extensions that are an alternative to traditional Common Gateway Interface (CGI) programs written in languages such as C, Perl or proprietary web server plugins that is Internet Server Application Programming Interface (ISAPI) or Netscape Server Application Programming Interface (NSAPI) extensions. Servlets are written in the Java programming language and conform to Sun Microsystems' Java servlet API (Application Programming Interface). In this implementation, the CGI programs have been replaced by JAVA-Servlets. Processing at the GIS server end is identical to the CGI approach.
Servlets are cross platform programs and are supported by all major web servers on all major operating systems. Servlets can be hosted on any web server on all major Operating Systems using a third party 'servlet' engine such as 'ServletExec'. Servlets once developed can be deployed anywhere over the network. Servlets have all the benefits of "write once, run anywhere" paradigm.
CORBA Approach
Common Object Request Broker Architecture (CORBA) is a middle ware architecture specification for distributed computing applications. It is a product of a consortium called Object Management Group (OMG). CORBA allows intelligent components to discover each other and inter-operate on an object bus. However CORBA goes beyond just interoperability. It also specifies an extensive set of bus-related services for creating and deleting objects, accessing them by name, storing them in persistent stores and defining ad-hoc relationship between them. CORBA lets you create an ordinary object and then make it transactional, secure, lockable and persistent by making the object multiply-inherit from the appropriate services. Processing at the GIS server end is identical to the CGI approach.
In NRIS decision to choose platform as well as GIS package is left to state's discretion. The CORBA approach has been explored for the NRIS project because of its numerous advantages in heterogeneous platform environment. The Object Request Broker allows objects written in different languages and residing in different platforms to communicate with each other. Thus a client written in one language can talk with a C/C++/JAVA/Ada/COBOL server. CORBA servers can run on different machines, which results in server scalability and load distribution hence better performance.
Comparative Study of Different Technologies
Different WEB implementation methodologies have been tested to decide the best approach for NRIS project. A specific application shell "SDSS (Spatial Decision Support Shell)" has been implemented using the three techniques viz. CGI, Java-Servlets & CORBA. The same shell SDSS has been provided to respective GIS vendors for development in their GIS environment. The shells developed by ESRI-India Ltd. using ARC/INFO & AVIMS and PCI Software Private Ltd. using SPANS and SPANS WEB SERVER have been evaluated.
CGI, Java-Servlets and CORBA techniques are OS independent. SPANS WEB SERVER is available only on WINDOWS/NT. AVIMS is available on both UNIX and WINDOWS/NT platforms. It is a single threaded process, thereby putting queries in queue, and deteriorating the response time. However the UNIX version is not tested. Both AVIMS and SPANS WEB SERVER require proprietary GIS. The other three techniques are not tied up to any specific GIS. Only, the GIS scripts will have to be in the language of the selected GIS. In the standard "MAP SERVER" approaches the response time was poor, the presentation of results was not impressive. In particular, the legends were truncated and screen utilization was not to the maximum possible. Also, multiple clients access was not consistent. Often results were posted to wrong clients. In a situation where two servers have related data in different GIS packages, the proprietary map server packages cannot communicate to each other.
Following
table
gives comparison between different technologies based on various parameters:
| Approach |
CGI |
Java Servlet |
CORBA |
ARC/INFO AVIMS |
Spans Web Server |
| Platform |
Win-NT & unix |
Win-NT & unix |
Win-NT & unix |
Win-NT & unix |
Win-NT only |
| Proprietary GIS |
No |
No |
No |
ARC/INFO |
Spans |
| Response Time |
Good |
Good |
Good |
Poor |
Not
Known |
| Presentation |
Good |
Good |
Good |
Poor |
Poor |
| Access Authorisation |
Yes |
Yes |
Yes |
Yes |
No |
| Integrated Planning and Querying |
Yes |
Yes |
Yes |
No |
No |
| Ease
of use |
Yes |
Yes |
Yes |
Yes |
No |
| Multiuser |
Yes |
Yes |
Yes |
No |
No |
| Systematic exit |
Yes |
Yes |
Yes |
No |
No |
| Procedures at server end |
No |
Servlet runner required |
Corba
setup required |
Invoke ARC/INFo & ARCVIEW |
Not
Known |
| Setup
at client end |
No |
No |
No |
Required on unix |
Not
Known |
Future Scenario
Efforts are being put by the technocrats of GIS products for providing standard mechanisms for display and manipulation of vector and graphics data in a Browser. Studies in this direction are on for providing more efficient live GIS access over a web. Object oriented GIS packages are also being analyzed for better throughput.
Recently web based GIS and virtual GIS based on 3D graphic technology are emerging issues in the field of GIS. Building a GIS with virtual reality capability and running on WWW is challenging, because the web based application should overcome the 3D graphical overhead with a pure software approach. A combination of Java and VRML has been tried out to build virtual GIS. The 3D primitive i.e. height, has been expanded from 2D primitives by adding the z-coordinates to points. Using this, display and viewing of 3D scene has been implemented with VRML. This work is being improvised and extended for additional functionality.
In phase II of NRIS a good number of state nodes will be operational. All the districts and line departments will access the state node over VSAT or dial-up connections for management and development activities. As of now, the in-house developed web applications seem to be the only solution. The technology developed in-house, will be transferred to industry, who will later be the focal points for the maintenance of these packages. The maintenance of such packages will be easier and more efficient, when standard products are used for application development. Under the GRAMSAT project, the CGI version is planned to be installed at ORRISSA.
Conclusion
The standard "WEB SERVER" approach can serve a user community where the users are limited and clients are not remotely located. The NRIS scenario is different. Here the clients are spread countrywide. The number of users at each node server is large (greater than 20). The mode of access could be via, VSAT or a dial-up (ISDN/PSTN) and in rare cases over a LAN. The node server being a state center, each state may opt for a different GIS package. Across states accessibility is also required. In this context the CGI or JAVA-Servlets or CORBA approach will turn out to be a more flexible and cost effective solution.
Acknowledgements
The authors express their thanks to Mr. A.K.S. Gopalan, Program Director NRIS and Mr. A.R. Dasgupta, Project Director, NRIS-SIP, for their constant encouragement and valuable suggestions throughout the course of this work. The authors are also thankful to the cooperation extended by team members of the NRIS Linkages and Networking Program and all members of the NRIS Systems and Integration Program, especially Mr. R.K. Goel, Head, Informatics Applications Division and Mr. P.M. Udani of Space Applications Center who were involved in the Test & Evaluation of the vendor developed web shell. Our special thanks to Mr. P.D. Yadav & Mr. B.G. Vaishnav of Space Applications Center, for providing valuable help in the VRML activity.