Data can be a strategic source of information. The process of knowledge discovery in databases allows valuable patterns and regularities to be discovered from the data alone. The knowledge so extracted is fundamental and leads to constructing systems of prediction, diagnosis and pattern recognition. Some examples are the following: text mining (automated indexing of documents based on contents), web user profiling (using the data collected at a web site to classify a customer), automated medical diagnoses, classification of loan applicants, market basket analysis (grouping goods that customers tend to buy together in a supermarket), predicting failures in manufacturing processes.