1. A natural language understanding system using at least one hardware implemented computer processor for automatic unsupervised clustering of dialog data from a natural language dialog application, the arrangement comprising: a log parser configured to extract structured dialog data from application logs; a dialog generalizing module configured to automatically generalize the extracted dialog data using different independent generalization methods to produce a generalization identifier vectors aggregating the results of the generalization methods used; and a data clustering module configured to automatically clustering the dialog data based on the generalization identifier vectors using an unsupervised density-based clustering algorithm without a predefined number of clusters and without a predefined distance threshold.