Re: Navigation question

dawn wrote:
> mAsterdam wrote:

>> dawn wrote:
>>> mAsterdam wrote:
[snip]

>>>> 'From a fk in a child to a parent tuple'
>>>> is at best metaphor (and btw. borrows hierarchical terms).
>>> Do these terms properly communicate so that you know what I mean,

> Let's say you are looking at a report, on paper, showing a set of
> attribute names and values for a Person with personId="77777"
> fmName="Danni Lynn" mother="11111". You put your finger on Danni
> Lynn's mother value. Then you realize that on that same piece of
> paper there are more values from the Person relation listed, including
> one with personId="11111" and fmName="Anna Nicole".
>
> So, you move your finger from "11111" as a value of the mother
> attribute to the "11111" that is a value of the personId attribute for
> another Person. This was physical navigation. You moved your finger
> on the paper.
>
> However, there is logical navigation that corresponds to this, where
> there was no need to move your finger as there is an algorithm that
> "goes from" the mother of one person to the personId of another. This
> algorithm is one example of going "From a fk in a child to a parent
> tuple"
>
> Now encode some bytes on a disk drive, for example, so that the
> logical interpretation of them is similar to what is on our paper
> (although the physical representation might be very different). The
> physical representation might even span disk drives. It has an
> algorithm that could be quite different from a corresponding logical
> (application coded) navigation. The application level, logical level,
> navigation would be at a higher level of abstraction than any physical
> navigation.

[snip]

> Add 8 "User Layer" to the OSI layers. My questions are regarding
> layer 7, where "logical navigation" of a database might take place.

The OSI layering hides the complexity
in the lower layer from the layers above it by hiding the concepts in the lower layer from the one above it, except for a clean request/service interface.

By using RM terms (what layer is that? - hm, dunno, but for the argument it only matters that it is lower than 8 in your stack) in the added layer 8 you are doing the opposite.

earlier:

 > The question is whether the logical navigation described above has
 > something inherently "bad" about it so that we must always avoid
 > coding such navigation into our applications (combination of
 > metadata and code, for example).

This would be about the application layer, right? (and still good/"bad", and still "logical navigation".) Received on Fri Feb 23 2007 - 09:06:58 CET