Middleware Support for Voting and Data Fusion

Middleware is a class of software systems above the op-erating system which is becoming widely used for program-ming distributed systems. Voting is a fundamental oper-ation when distributed systems involve replicated compo-nents. However, support for voting in middleware is very limited. This paper describes issues involved with support-ing 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 compan-ion Voting Definition Language (VDL), which allows for portable description of voting algorithms. The VVM and VDL, together with the external VVM voting manager, pro-vide for voting transparency and adaptive voting. Finally, we describe how the simple “byte-by-byte ” value compari-son 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.