Re: Constraints and Functional Dependencies
Date: Wed, 28 Feb 2007 17:20:11 GMT
Message-ID: <fRiFh.2475$PV3.33768_at_ursa-nb00s0.nbnet.nb.ca>
Marshall wrote:
> On Feb 27, 3:20 pm, "Tony D" <tonyisyour..._at_netscape.net> wrote:
>
>>I wish I could agree about the semantics, but I'm not yet convinced.
>
> I am impressed with the degree to which they've thought through
> every last detail of what needs to be possible with relations,
> and how it should work. This is the main value it seems to me.
> How they've organized it, choice of operators, syntax, etc.
> is merely okay.
>
>
>
>>I'm also not 100% convinced about the utility of possreps.
>
> For myself, I completely fail to see the point of possreps.
Data independence.
Consider a Complex number type. It has two possible representations:
cartesian and polar.
Consider the following chart of performance characteristics for
combinations of operations and representations:
| Cart | Polr |
Consider three similar relations that have a Complex attribute. The
first application mostly uses the attribute for addition. The second
application mostly uses the attribute for multiplication. The third uses
the attribute for a balanced mix of operations.
The first application will perform better if the dbms physically stores
+ | Fast | Slow |
Now, suppose it is the same relvar in all three cases and a dba has to achieve specific performance goals. How does the dba do that without disrupting any of the applications.
Finally, consider a Video data type where each conversion results in a loss of picture quality. What is the best way to support multiple players and formats? Received on Wed Feb 28 2007 - 18:20:11 CET