Structure of the DATASET node. The global node is DATASET, and is composed by one or more Case nodes. A Case node has an ID attribute for the identification of the case, and a sequence of nodes: first the Tissue node, with a Type attribute for the tumour type; and then a sequence of one or more Spectrum nodes. Every Spectrum node has three child nodes: Parameters, Points, and MapPosition. The Points node is used to store the spectral quantitative data, i.e. the intensity value of each point in the frequency domain, and the MapPosition node is used to store the x-y position of each spectrum in each MV grid. Dashed lines are used to indicate non-mandatory elements.