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Can data be 'over-normalized'?
Message
 
To
25/01/2001 13:13:41
General information
Forum:
Visual FoxPro
Category:
Databases,Tables, Views, Indexing and SQL syntax
Miscellaneous
Thread ID:
00468334
Message ID:
00468877
Views:
14
David,

Ok here's a brief intro to normalization.
1st Normal Form: There are no repeating or multivalued fields in the
                 table's structure.

2nd Normal Form: All fields are dependant on the entire primary key for their
                 values.

3rd Normal Form: All fields are dependant on ONLY the primary key for their 
                 values.

Boyce-Codd Normal Form: The table is in 3rd normal form for all feasible 
                        candidates for the primary key.

4th Normal Form: There are not independantly multivalued components of the 
                 primary key (for tables where the primary key is comprised
                 of two or more component fields).

5th Normal Form: There are no cyclical binary dependencies within the primary 
                 key (for tables where the primary key is comprised of three
                 or more component fields).
So from this you can see that the structure you described is not wholely a result of normalization. Example: A tabel of books where you have fields like this;

Field
BookTitle (this with Revision is the PK)
Revision (this with booktitle is the PK)
Author1
Author2
Author3
Category1
Category2
Category3
DatePublished
Copyrightdate
PublisherID
PublisherName
PublisherAddress

Now the field Author1 - 3 and Category1 - 3 are multivalued attributes and they violate 1st normal form.

The field CopyrightDate is only dependant on the booktitle alone and not the combination of the title and the revision therefore it is in violation of 2nd Normal Form.

The publisher's name and address are codependant on the publisherID, which is not the PK for this table, and therefore is in violation of 3rd normal form.

The see Boyce-Codd, 4th and 4th NF's we would need to invent different table structures.
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