A series of computational techniques are applied to interpret diagnostic data from JET (the joint European torus). Some of these techniques are applied in parallel by packages which produce results that can be integrated by other packages. The associated data flow starts from raw measurements stored in JPFs (JET pulse files) and runs through a hierarchy of PPFs (processed pulse files) containing calculated results. A small subset of these are extracted into a data bank and employed for statistical studies such as scaling laws. Examples of computational techniques and calculated results are given together with an overview of the organisation of data flow and code structures.