One disadvantage of allowing this condition to exist in a data warehouse is that additional, inter-record logic must be designed and programmed into the ETL so that all the necessary records are created each time a new set of key values is added.
Consequently, if a multivalued dependency exists in a table, we need to create more than one record to store the information associated with a given key value. Modelers on more advanced projects, however, believe it is necessary to insulate their database designs against another class of anomalies, namely multivalued dependencies, and this belief causes them to search their third normal form schemas for fourth and fifth normal form violations.Ī multivalued dependency exists if the keys of a table determine not just one occurrence of the remaining values in a table but instead multiple values. Some designers believe that moving a database to third normal form is sufficiently free of update anomalies and stop their design work there. Ralph Hughes MA, PMP, CSM, in Agile Data Warehousing for the Enterprise, 2016 4NF Correction
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