Encyclopedia of Machine Learning

2010 Edition
| Editors: Claude Sammut, Geoffrey I. Webb

String kernel

Reference work entry
DOI: https://doi.org/10.1007/978-0-387-30164-8_790

A string kernel is a function from any of various families of kernel functions (see  kernel methods) that operate over strings and sequences. The most typical example is as follows. Suppose that we are dealing with strings over a finite alphabet Σ. Given a string a = a1a2…an ∈ Σ*, we say that a substring p = p1p2…pkoccurs in a on positions i1i2…ik iff 1 ≤ i1 < i2 < … < ikn and aij = pj for all j = 1, …, k. We define the weight of this occurrence as \({\lambda }^{{i}_{k}-{i}_{1}-k+1}\)

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