Re: Navigation question

On Feb 19, 3:09 pm, "JOG" <j..._at_cs.nott.ac.uk> wrote:
> Ok, lets fix this confusion once and for all Dawn. This one /cannot/
> go wrong. I have every faith that this coming analogy will clear
> things up. No siree. Cannot fail.
>
> * Ok, consider a Declarative programming language. Say lisp (or
> Haskell, etc):
> * Obviously noone would say such a language is procedural - it just
> declares... and thats it.
> * /However/ if one had a system was configured such that given some
> user input, a different lisp program was fired up... well would that
> mean that lisp was now procedural? Of course not.
> * Thats how clear the separation in layers is.

I'm tempted to accept your analogy and will come close to doing so. However, my understanding of the aversion to navigation is that it is a problem with navigating "through a database" rather than strictly within some piece of code. I will accept that just because there was some travel through a database does not mean that the code did so on its own with no intervening events. You may choose not to call this database navigation or choose to indicate that this pattern constitutes acceptable database navigation. Additionally, I will accept that the code might not be navigating (I didn't say that it did) even if database navigation occurs, analogous to your example. Similarly, the software in your analogy does do sequential processing, even if the code is declarative.

> Its clear the 'navigation' began before the lisp program started. Its
> the exact same pattern when we query databases declaratively -
> navigation just doesn't happen, never, not a sausage at the logical
> layer. In theory.

So, if the software reads through the database from company to orders to line items to products based on the user moving through data, you would not say that the software navigates through the database, even if it is clear that the software product permits the user to do so. I'm OK with that.

So, the subsequent question is whether it is always wrong or poor practice for the software to perform similar steps, but without the user events between them? In that case the software would be navigating, right?

And the second question of whether it is OK for the DBMS to navigate based on user specifications of "links" (aka join information) in the case of a statement such as

select customerid, customerName, emailAddresses, classifiers, Order.orderid, Order.orderPrice from Customers where tin = 'xyz'

This is similar to an SQL statement that would get the same data, but with these differences:
1. The DBMS navigates (do you agree?)
2. There is no cross-product if the above statement returns a single row for this single customer, but with more complex attribute values (including two sets for emailAddresses and classifiers and a table for the order information).

It should be clear that there is a benefit to this approach (with 2), but the cost in this case is navigation. What is the downside of this type of navigation? Thanks. --dawn Received on Mon Feb 19 2007 - 23:07:06 CET