Data fusion is the name given to the process of combining multiple sources of (possibly heterogeneous) data. Arguably, the most widely used model is that developed by the Joint Directorate Laboratories. It illustrates how the collected information can be fused to produce a description of the situation and environment at several different layers of abstraction.
In my answer to a Quora question, I explain the model in detail and then talk about how it can be a powerful tool in the analysis of Big Data.
You can read my answer here.