Web sites are found by their addresses on the World Wide Web. These addresses are known as URLs, or Uniform Resource Locators. Every website has a URL assigned to it, so both searchers and Web servers can find them quickly and easily.
Cluster analysis or clustering is the task of grouping a set of objects in such a way that objects in the same group (called a cluster) are more similar (in some sense or another) to each other than to those in other groups (clusters).
Clustering is a fundamental data analysis method. It is widely used for pattern recognition, feature extraction, vector quantization (VQ), image segmentation, function approximation, and data mining. As an unsupervised classification technique, clustering identifies some inherent structures present in a set of objects based on a similarity measure.