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ery two minutes to check if the client is still alive, if for six minutes the client doesn抰 respond DCOM discards the client抯 request. CORBA on the other hand does not force the client to stay connected and does not use keep alive messaging. As DCOM uses keep alive messaging it is able to determine when to discard the request and it has built in garbage collection, while CORBA does not provide built in garbage collection mechanism.
Usage View:
COM/DCOM is Microsoft抯 proprietary architecture and is only supported on Windows family of operating systems. However, third party vendors provide support for DCOM on UNIX systems. DCOM is based on native binary format hence offers faster execution but is not portable to other platforms. COM/DCOM components have access to Windows API and can potentially damage or compromise user抯 computing environment. DCOM provides basic support for distributed objects but no support for real time processing or situations requiring high reliability. Although COM has been available for a while it is not clear weather its flavor DCOM will be equally effective in widely distributed applications.
CORBA is only a specification and not an implementation, so it抯 hard for buyers to determine if the product in consideration is fully CORBA compliant or not. Also there are no defined test suites for determining CORBA compliance. It is necessary for users to perform hands-on evaluation of vendor products. CORBA is complex specification and require a considerable expertise for develop distributed objects and applications. On the other hand, it is easier than previously available technologies for developing distributed applications. Still thorough expertise in distributed systems design, distributed and multi-threaded programming and debugging, inter-networking, object oriented design, analysis, and programming is required.
Usage Comparison:
Cross-platform support is very extensive in CORBA while COM/DCOM is limited to Microsoft operating systems. CORBA as well as COM support components written in multiple languages. CORBA Objects are based on a standard specification published in 1991 while COM抯 specifications and code are continuously changing and the documents are available only in draft format. COM was originally designed to run on single machine and was not designed for large-scale networks. However, CORBA was designed from scratch with large-scale distributed applications in consideration.
CORBA products are available from a wide variety of vendors while COM/DCOM is only available from Microsoft. As CORBA specification is defined by OMG a consortium of 800+ companies, its highly likely to reflect the demands of the industry as opposed to COM/DCOM, which is proprietary to Microsoft and Microsoft retains the final say in COM/DCOM specifications.
Conclusion:
COM/DCOM and CORBA are both scalable and robust architectures for distributed computing and offer different advantages. However, due to their inherent differences they are suitable for different sizes and types of applications and scenarios. COM/DCOM is suitable if the systems are predominantly running Microsoft抯 operating systems and the geographic distribution is not very wide spread. CORBA is suitable for heterogeneous and widely distributed systems. Both technologies have similarities and differences in their architecture and hence should be considered before choosing either one. Also, many vendors are offering solutions that allow CORBA applications to interact with COM and vise versa. Seems like COM/DCOM and CORBA will continue to compete vigorously and still co-exist for a long time to come.
Reference:
Microsoft Corporation (2001). COM Specification.
Tallman, O., & Kain, J. (1998). COM versus CORBA: A Decision Framework.
Brake, M. (1998). Explaining CORBA.
Object Management Group (2001). The Common Object Request Broker: Architecture and Specification.
Microsoft Corporation (1998). Microsoft Component Services.
Raj, J. (1998). Common Object Request Broker Architecture.
Software Engineering Institute (1997). Component Object Model (COM), DCOM, and Related Capabilities.
Software Engineering Institute (1997). Common Object Request Broker Architecture.
Microsoft Corporation (1996). DCOM Technical Overview.
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