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From "Michael J. Carey (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (ASTERIXDB-1778) Calculating the edit-distance in SimilarityMetricEditDistance class can be improved.
Date Thu, 02 Feb 2017 06:15:51 GMT

     [ https://issues.apache.org/jira/browse/ASTERIXDB-1778?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Michael J. Carey updated ASTERIXDB-1778:
----------------------------------------

Do we want that change, or should the optimized version be a differently 
named/used function that's invoked under the hood?





> Calculating the edit-distance in SimilarityMetricEditDistance class can be improved.
> ------------------------------------------------------------------------------------
>
>                 Key: ASTERIXDB-1778
>                 URL: https://issues.apache.org/jira/browse/ASTERIXDB-1778
>             Project: Apache AsterixDB
>          Issue Type: Improvement
>            Reporter: Taewoo Kim
>            Assignee: Taewoo Kim
>            Priority: Minor
>
> Local optimization of the current edit-distance handling code in AsterixDB: Can we terminate
the edit distance calculation based on a given edit-distance threshold T? I think the answer
is yes.
> Basic Algorithm:
> For two strings X and Y, 
> Init:
> Construct D(len(X)+1=M, len(Y)+1=N).
> D(i,0) = i
> D(j,0) = j
> Iteration:
> {code}
> For each i = 1 to M
>     For each j = 1 to N
>         D(i,j) = min( D(i-1,j) + 1 // deletion case
>                       D(i,j-1) + 1 // insertion case
>                       D(i-1,j-1) + cost (cost is 2 if X(i) != Y(j), 
>                                                  cost is 0 if X(i) = Y(j))
>                     )
> {code}
> Result:                    
> D(M,N) is the edit distance value.
> Example:
> Early Termination condition:
> So, for the given threshold T, we can stop the computation early if the values of three
cases are greater than T. That is,
> min (D(i-1,j), D(i,j-1), D(i-1,j-1)) > T
> This holds since if the cost of all possible cases (insertion, deletion, and substitution)
is greater than T, all future operations will be greater than T in any cases.



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