Re: Conceptual, Logical, and Physical views of data

On 8 Sep 2005 08:24:47 -0700, "dawn" <dawnwolthuis_at_gmail.com> wrote:

>Marshall Spight wrote:
>> dawn wrote:
>> >
>> > I do want navigational
>> > operators, however and that seems to go against relational theory. I
>> > want to "click on" a foreign key value and navigate to the referenced
>> > entity.
>>
>> Everything you can do with pointers you can do with relational
>> operators. Pointers are neither necessary nor sufficient for
>> "navigation"; that is, finding the data you want.
>
>In that case, the API I use could have what I want, even if behind the
>scenes it uses relational operators, which behind the scenes use
>navigation, right?

     The point of the RM is to hide the implementation details. Pointers might be used internally, but that is not the problem. When they get exposed though, you can have dependencies which are quite unncessary (and ugly to boot).

>> Addressing the data by its content, rather than by
>> its location,
>
>I'm all for addressing data by its content. I still don't know whether
>it is proper to call a foreign key a pointer or not, but it is surely
>data.

     Does it value depend on the location of the data? No, so it is not a pointer.

>> provides a proper superset of the
>> functionality of the navigational operators.
>
>Just to be sure I understand this last statement, what do you mean by
>"addressing data by its content, rather than by its location"? Other
>than specifying a data source, what would be an example of addressing
>data by location? Do you consider a base table name to be a location?

          select * from clients where clcode="ABC" is addressing by content.

          get client record 5
is addressing by location.

Sincerely,

Gene Wirchenko Received on Thu Sep 08 2005 - 19:41:27 CEST