Re: A Normalization Question

On Mon, 12 Jul 2004 15:54:08 -0700, Neo wrote:

>> Once you understand why we normalize you will understand why the notion of
>> redundancy is defined in database theory as it is and why multiple
>> occurrences of the same string in a data structure are not
>> necessarily redundant.

> 
> Multiple occurances of the same string is necessarily redundant. It
> requires a limited data model and definitions to obscure this fact.

This has nothing to do with the data model. The definition of logical redundancy is independent of what data model you choose.

>> > [...] Suppose, the world is taken oven by islamic terrorist. As part
>> > of their spoils, they want every word in every computer to be spelled
>> > backwards, thus 'brown' needs to be update to 'nworb'. [...] In the
>> > above tuple, updating one and not the others, corrupts the db.
>>
>> Yes, but only when you start from an instance that is not already an
>> instance from the new database schema is concerned. To show that either
>> instances of the new or the old database schema have redundancy you have
>> to demonstrate that there are update anomalies that stay within that
>> particular database schema.

> 
> In my data model, the data is the schema; however more general schemas
> could be derived from the data if needed.

That is besides the point.

> I am not sure what point you
> are making, but changing one 'brown' to 'nworb' in a db with multiple
> occurances of the same string results in an update anomaly.

Not according to the standard definition of update anomaly in normalization theory. It would really help communication if you stopped giving standard terminology your own Neo-meaning.

Note, by the way, that in your "normalized" representation you sometimes need two updates (the creation of a new list of characters plus the update of a reference) for what was originally only one update (updating a string). And this is the case for a very very common update whereas your example is a bit exotic, to say the least.

• Jan Hidders