Re: Constraints and Functional Dependencies

From: Bob Badour <>
Date: Wed, 28 Feb 2007 17:20:11 GMT
Message-ID: <fRiFh.2475$>

Marshall wrote:

> On Feb 27, 3:20 pm, "Tony D" <> 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 |

+ | Fast | Slow |
  • | Slow | Fast |

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 the attribute in cartesian coordinates. The second application will perform better if the dbms physically stores the attribute in polar coordinates. The third application performs better if it avoids unecessary conversions.

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

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