Lookup

LookUp is a term used in information systems to describe the process of retrieving data associated with a key or identifier from a dataset, database, or external service. In practice, LookUp can refer to the action of searching for a value given a key, a data structure that stores precomputed mappings, or a software feature that exposes such retrieval.

A LookUp table is a data structure that stores pairs of keys and values to enable fast data retrieval without recomputation. They can be implemented as arrays indexed by the key, hash tables, or balanced trees. Lookups may be performed in memory for speed or on storage devices for large datasets; caching can reduce latency.

Common forms include associative arrays or dictionaries in programming languages, such as a Python dict or Java Map, and SQL joins that retrieve related rows. In spreadsheets, functions such as LOOKUP or VLOOKUP perform key-based retrieval across ranges.

Performance considerations center on time and space costs. Hash-based lookups typically offer expected constant time, while ordered structures provide logarithmic time. Precomputed LookUp tables save computation at the expense of extra storage and potential data staleness; updates may require synchronization.

Applications include configuration stores, localization dictionaries, DNS resolution, and reference data in software systems. Lookups are also used in indexing, caching, and data integration tasks to translate keys into human-readable labels or system values.

See also Look up, lookup table, dictionary, hash map, and reverse lookup.