Isub/4

Help!
1

I’m using: SWI-Prolog (threaded, 64 bits, version 8.1.15)

I want the code to: calculate the normalized Levenshtein Distance as implemented in isub/4.

My code looks like this:

?- isub('Andesite', 'Enderbite', false, D).
D = 0.8008578431372549.

?- isub('Andesite', 'Enderbite', true, D).
D = 0.8008578431372549.

I do not understand the normalization, nor the role of the third parameter. Can . anyone please tell me what is going on here?

Thanks

2

In the docs:

If Normalize is true , isub/4 applies string normalization as implemented by the original authors: Text1 and Text2 are mapped to lowercase and the characters "._ " are removed. Lowercase mapping is done with the C-library function towlower() . In general, the required normalization is domain dependent and is better left to the caller.

It “normalizes” the first and second argument before comparing. Here is an example where it makes a difference:

?- isub('BANANA', ananas, false, D).
D = 0.0.

?- isub('BANANA', ananas, true, D).
D = 0.8974358974358975.

I don’t know if D is “the normalized Levenshtein distance”. From the docs:

… a similarity measure between strings, i.e., something similar to the Levenshtein distance . This method is based on the length of common substrings.

I didn’t bother to read the C source too carefully but you must do it if you want to know what is really being calculated.

3

It is not doing Levenstein distance. See "A string metric for ontology alignment* by Giorgos Stoilos, 2005. As far as I recall, they do something that they claim works better. It works best for single word names/identifiers, etc. Still, these distance measures are fully domain independent and do not take into considerations that some letter (sequences) are considered very close to other letter (sequences) and this is language dependent.

4

Thank you Jan and Boris: I now understand that “normalization” refers to the strings and not to the Levenshtein distance. May I suggest that the documentation of isub/4 refer to the Solios paper explicitly? Thanks again for your help!

5

I think it is there already. If you open the section docs, you should see it at the very top:

author
Giorgos Stoilos
See also
A string metric for ontology alignment by Giorgos Stoilos, 2005.

6

Thanks Boris for pointing this out to me. I was looking at this page,

https://www.swi-prolog.org/pldoc/doc_for?object=isub/4

and it was not immediately obvious to me to expand on the link on the left to see that reference.

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