Information Technology Reference
In-Depth Information
Chapter 9
Data Normalization
Database normalization aims to remove irregularity (abnormality) of update. The
correctness of database after update is difficult to maintain in the unnormalized
database, whereas the normalized database is more user friendly for update. On the
other hand, the denormalization is the reverse of normalization. It transforms the
normalized database design into unnormal form (UNF). As a result, the denormal-
ized database is difficult to update. Nevertheless, the denormalized database can
perform faster than normalized database because it requires less joint operations for
query. Also, data normalization eliminates redundant data for better space utiliza-
tion and user friendliness in database update.
The XML data normalization requires an XML data modeling with minimum
fragments among elements. The normalized XML database design shows how to
eliminate data redundancy by replacing repeating data with pointers referring to
their unique primary copy element under root element. The minimum fragments
XML design is more efficient and is derived from a minimum closure of data de-
pendencies of representation of the data semantics among elements as a fragment
under root element.
9.1
Relational Data Normalization Without Update
Irregularity
Relational data normalization is to eliminate data redundancy and update irregular-
ity of relational schema. Irregularity of database design need to be normalized in
order to ensure user friendliness of updating relational database.
There is UNF, followed by first, second, third, Boyce-Codd, fourth and fifth
normal form. The higher normal form implies the lower normal form, but not vice
versa. We need to analyze data dependency to determine data normal form. Data
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