The issue is there is a database with around 20k customer records and I want to make a best effort to avoid duplicate entries. The database is Microsoft SQL Server 2005, the application that maintains that database is Microsoft Dynamics/SL. I am creating an ASP.NET webservice that interacts with that database. My service can insert customer records into the database, read records from it, or modify those records. Either in my webservice, or through MS Dynamics, or in Sql Server, I would like to give a list of possible matches before a user confirms a new record add.
So the user would submit a record, if it seems to be unique, the record will save and return a new ID. If there are possible duplications, the user can then resubmit with a confirmation saying, ‘yes, I see the possible duplicates, this is a new record, and I want to submit it’.
This is easy if it is just a punctuation or space thing (such as if you are entering ‘Company, Inc.’ and there is a ‘Company Inc’ in the database, But what if there is slight changes such as ‘Company Corp.’ instead of ‘Company Inc’ or if there is a fat fingered misspelling, such as ‘Cmpany, Inc.’ Is it even possible to return records like that in the list? If it’s absolutely not possible, I’ll deal with what I have. It just causes more work later on, if records need to be merged due to duplications.
The specifics of which algorithm will work best for you depends greatly on your domain, so I’d suggest experimenting with a few different ones – you may even need to combine a few to get optimal results. Abbreviations, especially domain specific ones, may need to be preprocessed or standardized as well.
For the names, you’d probably be best off with a phonetic algorithm – which takes into account pronunciation. These will score Smith and Schmidt close together, as they are easy to confuse when saying the words. Double Metaphone is a good first choice.
For fat fingering, you’d probably be better off with an edit distance algorithm – which gives a ‘difference’ between 2 words. These would score Smith and Smoth close together – even though the 2 may slip through the phonetic search.
T-SQL has SOUNDEX and DIFFERENCE – but they are pretty poor. A Levenshtein variant is the canonical choice, but there’s other good choices – most of which are fairly easy to implement in C#, if you can’t find a suitably licensed implementation.
All of these are going to be much easier to code/use from C# than T-SQL (though I did find double metaphone in a horrendous abuse of T-SQL that may work in SQL).
Though this example is in Access (and I’ve never actually looked at the code, or used the implementation) the included presentation gives a fairly good idea of what you’ll probably end up needing to do. The code is probably worth a look, and perhaps a port from VBA.