Keyline or also called Match Key is a combination of numbers and letters usually beginning with the zip code, used as a rough household duplicate eliminator. It is also an alpha numeric combination, usually with a zip code and is used to de-dupe addresses on a mailing list. With the use of keyline one can eliminate all duplicate entries from a list or a database. This is neccessary to do, to keep your database infrasructure clean. There are some method of doing this. But one of the most common form of deduplication implementations works in that way that it compares pieces of data do find duplicates. . For that to happen, each chunk of data is assigned an identification, calculated by the software, typically using cryptographic hash functions. In many implementations, the assumption is made that if the identification is identical, the data is identical, even though this cannot be true in all cases due to the pigenhole priciple; other implementations do not assume that two blocks of data with the same identifier are identical, but actually verify that data with the same identification is identical.If the software either assumes that a given identification already exists in the deduplication namespace or actually verifies the identity of the two blocks of data, depending on the implementation, then it will replace that duplicate chunk with a link.