I. Introduction
Modern biology presents new challenges in terms of data management, query and analysis. In cancer research Microarray development has enabled researchers to obtain gene expression data from the most diverse and complex biological phenomena. Obtaining the data is only the first step towards the discovery of the unknown types of cancer. To transform gene expression data into knowledge, clustering is the frequently used method; it aims at extracting hidden relationships between genes by grouping them into several clusters, within each cluster a set of genes share a common features.