This document summarizes techniques for desktop search engines, including feature extraction using entity recognition, query understanding using part-of-speech tagging and segmentation, and similarity measures for scoring and ranking documents. It discusses using ontologies, concept graphs, semantic networks, and vector space models to represent knowledge in documents. Feature extraction identifies entities that can be mapped to knowledge bases to infer meanings. Query understanding aims to determine intent regardless of technique used. Similarity is measured using approaches like comparing maximum common subgraphs between a document and query graphs.