Search engine indexing entails how data is collected, parsed, and stored to facilitate fast and accurate retrieval. Index design incorporates interdisciplinary concepts from Linguistics, Cognitive psychology, Mathematics, Informatics, Physics, and Computer science. An alternate name for the process is Web indexing, within the context of search engines designed to find web pages on the Internet.
Popular engines focus on the full-text indexing of online, natural language documents, yet there are other searchable media types such as video, audio, and graphics. Meta search engines reuse the indices of other services and do not store a local index, whereas cache-based search engines permanently store the index along with the corpus. Unlike full text indices, partial text services restrict the depth indexed to reduce index size. Larger services typically perform indexing at a predetermined interval due to the required time and processing costs, whereas agent-based search engines index in real time.