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Message Posted: Thu, 01 Dec 2011 @ 10:36:12 GMT

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Subj:   Re: Surrogate key usage
From:   Kenneth Hansen

SKs are invaluable in protecting the DW from natural keys which are re-used/circulated on source systems. Most people claim the natural key is unique but only in the sense of those that are live at a moment in time.

Most operational systems cannot guarantee to not use/create an ID for a new customer or account or order, etc., that has never been used before.

Secondly, if the table is to accept data from multiple sources and the natural keys vary either in number of attributes or datatype e.g. numeric on one and alphanumeric on another, the SK provides the common denominator. And do not forget that the additional sources may not be identified until several years after the databasemodel is implemented. SKs could be seen as "future proofing".

Third, SKs are increasingly used in progressive FIs to mask the external identity of accounts, cards and customers in order to increase confidentiality. Many who are used to being trusted may take offence but in reality no true analyst needs access to data that could be useful for identity theft!

BUT - beware use of Teradata Identity Columns for SKs. The latest Teradata Partners and the Teradata Magazine Q32011 announced that Unity would be the Teradata tool for data replication. That tool does not support Identity Columns because it relies on dual load. Obviously load to a second instance of Teradata will rarely get the same ID so customers are faced with the choice of an alternative method/tool for replication or creation of SK needs to be done in the Load process

Good luck,

Kenneth Hansen

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