"padding" bitmaps to support similarity and mining

The current paper presents a novel approach to bitmap-indexing for data mining purposes. Currently bitmap-indexing enables efficient data storage and retrieval, but is limited in terms of similarity measurement, and hence as regards classification, clustering and data mining. Bitmap-indexes mainly fit nominal discrete attributes and thus unattractive for widespread use, which requires the ability to handle continuous data in a raw format. The current research describes a scheme for representing ordinal and continuous data by applying the concept of "padding" where each discrete nominal data value is transformed into a range of nominal-discrete values. This "padding" is done by adding adjacent bits "around" the original value (bin). The padding factor, i.e.; the number of adjacent bits added, is calculated from the first and second derivative degrees of each attribute's domain-distribution. The padded representation better supports similarity measures, and therefore improves the accuracy of clustering and mining. The advantages of padding bitmaps are demonstrated on Fisher's Iris dataset.