In mathematics and computer science, a string metric (also known as a string similarity metric or string distance function) is a metric that measures distance ("inverse similarity") between two text strings for approximate string matching or comparison and in fuzzy string searching. A requirement for a string metric (e.g. in contrast to string matching) is fulfillment of the triangle inequality. For example, the strings "Sam" and "Samuel" can be considered to be close. A string metric provides a number indicating an algorithm-specific indication of distance. The most widely known string metric is a rudimentary one called the Levenshtein distance (also known as edit distance). It operates between two input strings, returning a number equivalent to the number of substitutions and deletions needed in order to transform one input string into another. Simplistic string metrics such as Levenshtein distance have expanded to include phonetic, token, grammatical and character-based methods of statistical comparisons. String metrics are used heavily in information integration and are currently used in areas including fraud detection, fingerprint analysis, plagiarism detection, ontology merging, DNA analysis, RNA analysis, image analysis, evidence-based machine learning, database data deduplication, data mining, incremental search, data integration, Malware Detection, and semantic knowledge integration. List of string metrics Levenshtein distance, or its generalization edit distance Damerau–Levenshtein distance Sørensen–Dice coefficient Block distance or L1 distance or City block distance Hamming distance Jaro–Winkler distance Simple matching coefficient (SMC) Jaccard similarity or Jaccard coefficient or Tanimoto coefficient Tversky index Overlap coefficient Variational distance Hellinger distance or Bhattacharyya distance Information radius (Jensen–Shannon divergence) Skew divergence Confusion probability Tau metric, an approximation of the Kullback–Leibler divergence Fellegi and Sunters metric (SFS) Maximal matches Grammar-based distance TFIDF distance metric Selected string measures examples References External links String Similarity Metrics for Information Integration A fairly complete overview Carnegie Mellon University open source library StringMetric project a Scala library of string metrics and phonetic algorithms Natural project a JavaScript natural language processing library which includes implementations of popular string metrics Metrics