Middleware support for voting and data fusion

Middleware is a class of software systems above the operating system which is becoming widely used for programming distributed systems. Voting is a fundamental operation when distributed systems involve replicated components. However support for voting in middleware is very limited. The paper describes issues involved with supporting voting, and more general data fusion, in middleware. We describe the Voting Virtual Machine (VVM) architecture, which can be embedded in different middleware substrates such as .NET and CORBA. We also describe its companion Voting Definition Language (VDL), which allows for portable description of voting algorithms. The VVM and VDL, together with the external VVM voting manager provide for voting transparency and adaptive voting. Finally, we describe how the simple "byte-by-byte" value comparison schemes used in other voting middleware as well as in byzantine fault tolerant multicast systems do not work in the face of the heterogeneity inherent in distributed systems.