11.9 Other Directions

11.9 Other Directions

This whistle-stop tour of the territory covered by the data survey has only touched briefly on a number of useful topics. A survey does much more, providing the miner with a considerable amount of information prior to mining. The survey looks at data sets from several other perspectives.

For instance, individual variable distributions are mapped and compared. Recall from Chapter 7 that much useful information can be discovered from the actual shape of the distribution?some idea of underlying generating processes or biases. The survey maps similarities and differences. Sensitivity analysis is another area surveyed?areas where the manifold is most sensitive to changes in the data.

The survey also uses three metaphors for examining data. Two have been used in the chapters on data preparation??manifolds? and ?shapes.? A manifold is a flexible structure fitted in some way to the data set. The metaphor of a shape regards all of the data points as ?corners? and regards the data set as creating some multidimensional structure.

The other useful metaphor used in the survey is that of a tensegrity structure . Tensegrity structures are sometimes seen as sculpture. The tensegrity structure is made of beams and wires. The beams are rigid and resist compression. The wires are in tension. This ?string and poles? structure, as a sculpture, forms a three-dimensional object that is self-supporting. The compression in the beams is offset by the tension in the wires. (As a matter of interest, tensegrity structures occur naturally as, for instance, the...

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