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Posted by Anith Sen on 11/02/06 17:14
Louis,
>> Date seems to be an attribute of an Order (correct me if I'm wrong) and
>> Price seems to be an attribute of a product, so price would need to be in
>> a products table and Date would need to be in an orders table.
Since Eddie did not post any information regarding the underlying business
model, how can we conclude what the actual entities and relationships are?
Perhaps it could be a table that represents pricing variations of some
product or service on a given date at three different locations or on three
distinct times or simply three samplings for statistical purposes.
We cannot know if a table is sufficiently normalized or not, unless we fully
comprehend the underlying business model and rules.
>> The fact that you have a lot of repeating groups, e.g. 100|100|100 shows
>> that the data isn't properly normalised.
How do we know if there is a repeating group however? Would you consider a
table like the following not to be properly normalized, given that you have
key column and a few datetime columns?
EmployeeHistory ( emp_id, b_date, a_date, h_date, t_date )
-- with the abbreviated names b_date, a_date, h_date and t_date to stand for
birth_date, applied_date, hire_date and terminated_date respectively.
A repeating group is a rampantly abused term that, for historical reasons,
means a group of values in a column. It does not suggest a repeating set of
similarly named columns in a table, though quite a few online sources
mistakenly state so. In the original post, there is nothing that suggests
the existence of a "repeating group". You have a simple table with four
columns -- essentially four distinctly named, typed attributes with scalar
values, where each non-key attributes are functionally dependant on the key
attribute.
Nothing in his post so far has suggested there are any normalization issues
either. And the problem he posed does not suggest the lack of normalization
either.
Very few online references are useful for learning fundamentals. One of
them, esp for 1NF is:
http://www.dbdebunk.com/page/page/629796.htm
The right way to learn normalization is to use good books. As for a
recommendation consider:
http://www.amazon.com/gp/product/0321197844/
http://www.amazon.com/dp/0596100124/
--
Anith
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