About Intelligent Keys and Column Values in Oracle Databases

on June 3, 2015

In Oracle, intelligent keys are so named because they contain nontrivial combinations of information. The term is misleading in the extreme because it implies something positive or worthwhile. A more meaningful term might be overloaded keys. General ledger and product codes often fall into this category and contain all the difficulties associated with other codes, and more. Further, the difficulties found in overloaded keys also apply to non-key columns that are packed with more than one piece of meaningful data.

Typical of an overloaded key or column value is this description: “The first character is the region code. The next four characters are the catalog number. The final digit is the cost center code, unless this is an imported part, in which case an I is tagged onto the end of the number, or unless it is a high-volume item, such as screws, in which case only three digits are used for catalog number, and the region code is HD.”

Eliminating overloaded key and column values is essential in good relational design. The dependencies built on pieces of these keys (usually foreign keys into other tables) are all at risk if the structure is maintained. Unfortunately, many application areas have overloaded keys that have been used for years and are deeply embedded in the company’s tasks. Some of them were created during earlier efforts at automation, using databases that could not support multiple key columns for composite keys. Others came about through historical accretion, by forcing a short code, usually numeric, to mean more and to cover more cases than it was ever intended to at the beginning. Eliminating the existing overloaded keys may have practical ramifications that make it impossible to do immediately. This makes building a new relational application more difficult.

The solution to this problem is to create a new set of keys, both primary and foreign, that properly normalizes the data; then, make sure people can access tables only through these new keys. The overloaded key is then kept as an additional, and unique, table column. Access to it is still possible using historical methods (matching the overloaded key in a query, for instance), but the newly structured keys are promoted as the preferred access method. Over time, with proper training, users will gravitate to the new keys. Eventually, the overloaded keys (and other overloaded column values) can simply be NULLed out or dropped from the table.

Failing to eliminate overloaded keys and values makes extracting information from the database, validating the values, ensuring data integrity, and modifying the structure all extremely difficult and costly.

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