Exploring the Data Structure

As described in section 6.3, having reached a particular point in the data structure by scanning, it is then possible to access related banks by following links. However, powerful as this method is, it cannot be used when:-

• Too many links steps are required (currently only 4 are allowed).

• The path to the target bank from the scanned point is not a fixed number of steps.

For example, having found which PMT a photon has struck, link stepping cannot be used to find the creation vertex of the photon, for there is no way of telling how many steps are required, and probably too many will required in any case. To address this and related problems, special DQFs have written to support backtracking, jumping and copying, which effectively allows simple programming of the n-tuple.