I would like to use a regualr expression on certain fields to detect possible duplicate records. for example the regx will detect all account records with the account name matching for than 50 %.possible duplicate acct names: AMC NY, NY AMC, NY & NYC, AMC LA.
What about using the standard salesforce duplicate management tool. https://help.salesforce.com/apex/HTViewHelpDoc?id=duplicate_prevention_map_of_tasks.htm&language=en_US
If your logic is too complex to support the duplicate management then you may need to write custom apex to achieve your result.