A new taxonomy of sublinear right-to-left scanning keyword pattern matching algorithms

A new taxonomy of sublinear (multiple) keyword pattern matching algorithms is presented. Based on an earlier taxonomy by the second and third author, this new taxonomy includes not only suffix-based algorithms, but also factor- and factor oracle-based algorithms. In particular, we show how suffix-based (Commentz-Walter like), factor- and factor oracle-based sublinear keyword pattern matching algorithms can be seen as instantiations of a general sublinear algorithm skeleton. During processing, such algorithms shift or jump through the text in a forward or left-to-right direction, and read backward or right-to-left starting from positions in the text, i.e. they read suffixes of certain prefixes of the text. They use finite automata for efficient computation of string membership in a certain language. In addition, we show shift functions defined for the suffix-based algorithms to be reusable for factor- and factor oracle-based algorithms. The taxonomy is based on deriving the algorithms from a common starting point by adding algorithm and problem details, to arrive at efficient or well-known algorithms. Such a presentation provides correctness arguments for the algorithms as well as clarity on how the algorithms are related to one another. In addition, it is helpful in the construction of a toolkit of the algorithms.