Are CORBA Services Ready to Support Resource Management Middleware for Heterogeneous Computing?

The goal of this paper is to report our findings as to which CORBA services are ready to support dis tributed system software in a heterogeneous environment. In particular, we implemented intercommunication between components in our Management System for Heterogeneous Networks (MSHN) using four dif ferent CORBA mechanisms: the Static Invocation In terface (SII), the Dynamic Invocation Interface ( DII), Untyped Event Services, and Typed Event Services. MSHN 's goals are to manage dynamically changing sets of heterogeneous adaptive applications in a het erogeneous environment We found these mechanisms at various stages of maturity , resulting in some being less useful than others . In addition we found that the overhead added by CORBA varied from a low of 10.6 milliseconds per service request to a high of 279.1 mil liseconds per service request on workstations connec ted via Mbits/ sec Ethernet. We therefore conclude that using CORBA not only substantially decreases the amount of time required to implement distributed system software but it need not degrade performance

RADGIS - an improved architecture for runtime-extensible, distributed GIS applications

A number of GIS architectures and technologies have emerged recently to facilitate the visualisation and processing of geospatial data over the Web. The work presented in this dissertation builds on these efforts and undertakes to overcome some of the major problems with traditional GIS client architectures, including application bloat, lack of customisability, and lack of interoperability between GIS products. In this dissertation we describe how a new client-side GIS architecture was developed and implemented as a proof-of-concept application called RADGIS, which is based on open standards and emerging distributed component-based software paradigms. RADGIS reflects the current trend in development focus from Web browser-based applications to customised clients, based on open standards, that make use of distributed Web services. While much attention has been paid to exposing data on the Web, there is growing momentum towards providing “value-added” services. A good example of this is the tremendous industry interest in the provision of location-based services, which has been discussed as a special use-case of our RADGIS architecture. Thus, in the near future client applications will not simply be used to access data transparently, but will also become facilitators for the location-transparent invocation of local and remote services. This flexible architecture will ensure that data can be stored and processed independently of the location of the client that wishes to view or interact with it. Our RADGIS application enables content developers and end-users to create and/or customise GIS applications dynamically at runtime through the incorporation of GIS services. This ensures that the client application has the flexibility to withstand changing levels of expertise or user requirements. These GIS services are implemented as components that execute locally on the client machine, or as remote CORBA Objects or EJBs. Assembly and deployment of these components is achieved using a specialised XML descriptor. This XML descriptor is written using a markup language that we developed specifically for this purpose, called DGCML, which contains deployment information, as well as a GUI specification and links to an XML-based help system that can be merged with the RADGIS client application’s existing help system. Thus, no additional requirements are imposed on object developers by the RADGIS architecture, i.e. there is no need to rewrite existing objects since DGCML acts as a runtime-customisable wrapper, allowing existing objects to be utilised by RADGIS. While the focus of this thesis has been on overcoming the above-mentioned problems with traditional GIS applications, the work described here can also be applied in a much broader context, especially in the development of highly customisable client applications that are able to integrate Web services at runtime