Re: Constraints and Functional Dependencies

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Tue, 06 Mar 2007 15:27:07 GMT
Message-ID: <fLfHh.7014$PV3.63041@ursa-nb00s0.nbnet.nb.ca>

paul c wrote:

> Marshall wrote:
> ...
>

>> In the case of lossy compression, I feel strongly that it is a logical
>> matter, and cannot be abstracted away. The choice of compression
>> ratios and algorithms needs to be under user/application control,
>> not dba control.

>
> Suppose a relation has a candidate key I which is an image of one person
> and another candidate key N which is the name of that person.
>
> 1) With possrep's, could some images in the same relation be represented
> in TIF format and others in JPG?

With possreps, the relation could have an image attribute where the dbms represents every image value as both TIFF and JPEG regardless of how it is actually stored.

> 2) When inserting a TIF image of one person or a JPG of the same person,
> is there a way an engine could consider the TIF and JPG equal?
>
> Does this have to do with what you mean?

Yes one can define equality similar to the way one can define equality for floating point numbers. Most well-written code avoids equality tests for floats due to rounding errors. Instead, one computes some distance measure and accepts as equal any two values differing less than some acceptable limit. Received on Tue Mar 06 2007 - 09:27:07 CST