1. A search engine for searching based on related scientific or technological concepts, comprising: a learning module for learning about relationships between technological terms based on their rates of occurrence in related documents, therefrom to form concepts from groupings of related phrases, and a search module for searching for relevant documents to a query document based on occurrence in said relevant documents of concepts present in said query document, wherein the learning module carries out said learning based on a training set of documents and inter-document relations and wherein said inter-document relations in said training set are derived from expert-provided reports.