Our customer owns and operates water theme parks. Last year, he had induced a couple of small-time firms to solicit customers to purchase theme park tickets. The problem at hand now is with one of the small-time firms--let's call it Solit. Solit claims that in the last quarter, it was able to channel close to 15,000 customers to buy tickets at the various theme parks. Neither our customer nor Solit has an exact list of the customers. Both of them have their own database of customers. The problem at hand is how many exact customers were channeled by Solit? The data contains the first name, middle name, last name, and date of birth of the customers. Keep in mind the data fields can differ slightly, for example, two records referring to the same entity, say John, may have a small change in the last name or a slightly different date of birth:

The preceding image is a snapshot of the data from our customer and Solit. Assume that we have merged the database records from both the parties. The record number indicates the source of the record, that is whether they came from our customer or Solit. If we can find duplicates in this dataset, that should serve as the first step in identifying the customers channeled by Solit.