A search engine and system for data, such as Internet web pages, including a query analyser for processing a query to assign respective weights to terms of the query and to generate a query vector including the weights, and an index network responsive to the query vector to output at least one index to data in response to the query. The index network is a self-generating neural network built using training examples derived from a feature extractor. The feature extractor is used during both the search and training phase. A clusterer is used to group search results.