Hierarchical clustering and bitmap indexes (okładka  miękka)

Decision support systems (DSS) works in read-mostly environment, which are subjugated by composite ad hoc queries that tend to, have high found sets. Normally Bitmap indexing is used to process complex queries in DSS. A bitmap file for indexed attribute comprises of one vector of bitmap or bits-strings per attribute value, with cardinality of the indexed relation is equal to the size of each bitmap. Bitmap indexing commonly used in data warehousing, OLAP and scientific applications for indexing of high dimensional data, all these applications, may have either complex or multi-dimensional ad-hoc queries for data of type read only. Bitmap indices are also very competent for Boolean logic at the bit level to evaluate query based on predicates and hence increased system response. Aggregate function such as COUNT, AVG (average) and SUM queries, whose results do not depend on the table while bitmap indexes are used, improve system performance as in case of OLAP application mostly queries are pre-defined aggregate values. Clustering can either be defined as exclusive to other objects which belong only to a single group or there may be some may belong to more than one class