A general view of the multi-source data fusion process is presented. Some of the considerations and information that must go into the development of a multisource data fusion algorithm are described. Features that play a role in expressing user requirements are also described. We provide a general framework for data fusion based on a voting like process that tries to adjudicate conflict among the data. We discuss idea of a compatibility relationship and introduce several important examples of these relationships. We show that our formulation results in some conditions on the fused value implying that the fusion process has the nature of a mean type aggregation. Situations in which the sources have different credibility weights are considered. We present a concept of reasonableness as a means for including in the fusion process any information available other then that provided by the sources. We consider the situation where we allow our fused values to be granular objects such as linguistic terms or subsets.