A method for estimation of the distance from a domain by means of a fragment based model, the method comprising the steps of identifying the fragments [r 1 to r n ] in a structure. Comparing the or each fragment with one or more fragments in the model. If the or each fragment substantially matches a fragment in a model determining a first error measure between the activity of the or each fragment and activity of the matching fragment in the model. If the or each fragment does not substantially match a fragment in the model determining which fragment in the model is the most similar to the or each fragment and determining a second error measure based on the similarity between the fragment and the most similar fragment. A step of combining the first error measure and the second error measure to generate a degree of separation between the activity of the structure and of the combined fragments in the model is then carried out. This method allows the calculation of a prediction even if there is the problem of missing fragments and allows a level of uncertainty (error) to be determined for the prediction.