Re: Navigation question

On Feb 21, 2:01 am, mAsterdam <mAster..._at_vrijdag.org> wrote:
> dawn wrote:
> > In another thread "navigation" is again mentioned as undesirable.
>
> Navigation is from here to there.
> Things like distance, direction, movement, traveling time, location,
> path and space are relevant concepts.
>
> In RM the database (at the logical level(*)) is a single-point
> thing. No navigational term has any meaning in a
> single point. Conversely, non of the RM terms
> have any navigational meaning.

Agreed. So, this discussion about navigation is outside of the RM.

> (*) Some may maintain that the RM covers no other level.
> A lower, physical level is implied, and AFAIK most
> book that cover RM also touch it. A lot of
> navigation is going on at that level. Without further
> qualification, every navigational remark is, by default
> about that level, the physical level.
>
> Nothing good, nothing bad here, just: navigation is something that
> does not exist within the RM.

Right. I do not know if navigation is often spoken ill of in this forum 1) because it is outside of the RM 2) for the same reasons that it is outside of the RM, whatever those might be or 3) for other reasons. I'm trying to understand what about database navigation is considered "bad" and why.

> '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, or is there some better way to say this?

> Now why do people (seem to) want to discuss RM at
> the exclusion of anything else? I don't know. I know I don't.

Perhaps my question was thought to be a question from within the RM, in which case it would be non-sensical, because, as you indicate, there is no such concept as "navigation" in the RM.

> You want to discuss navigation? Ok. The RM will not proliferate
> vocabulary. Furthermore, the first thing people will associate
> it with is the physical level hidden by the DBMS. You have clearly
> stated that that is not what you want to talk about.

Correct.

> Let's go navigating the database - not at the physical level, but
> somewhere else; 'Navigating foreign keys', example:
>
> Let's have a db browser like this:
>
> In the top-bar you can select any table (say A) from the schema,
> directly below it you can see all data in A
> in a spreadsheet display.
>
> In the second bar you can select any table (say B) having a foreign
> key referencing A. Directly below it etc...
>
> Now expand it (release 2) to a network browser,
> where it is possible have a place for selecting data from all tables C
> referenced by the foreign keys in B.
>
> This is something one could describe in navigational terms,
> loosely borrowing RM terms.
> Navigation here is the metaphor serving as a guideline for the user
> interface.

Yes. My understanding from responses to date is that thie type of navigation is not considered bad and not considered logical navigation, but more of a user interface conceptual navigation. Each user event permits us to start anew so that the code does not navigate the database, only the user does. So, while the physical is at a lower level than I want to discuss navigation, user-event driven "navigation" of a database is at a higher level.

> Release 3 would add the extra luxury feature of not just
> having foreign keys as paths between tables, but any join.

Yes. I mention foreign keys simply because they are easy to understand (I think) as "links" recognizing that one must step outside of the RM to do so. Cheers! --dawn Received on Wed Feb 21 2007 - 14:58:10 CET