Most organisations have information in various places that they are either unable (perhaps for governance reasons or because the data is incompatible) or unwilling (either for organisational or cost reasons) to consolidate into a single data store. Nevertheless, companies frequently want to be able to combine this disparate information, for a variety of potential reasons that we will come to in a moment. One way to do this is to hard wire links between the various applications and data sources involved. However, this is expensive, time consuming and, above all, it is inflexible. An alternative approach is to use data virtualisation (sometimes referred to as data federation or enterprise information integration-EII), which does not require specifically programmed links and which, as a result, is flexible rather than constrained.