Re: Navigation question

"dawn" <dawnwolthuis_at_gmail.com> wrote in message news:1172461549.849566.309620_at_j27g2000cwj.googlegroups.com...
> On Feb 25, 4:58 pm, "dawn" <dawnwolth..._at_gmail.com> wrote:
> > On Feb 23, 10:10 am, "Walt" <wami..._at_verizon.net> wrote:
> >
> > > "dawn" <dawnwolth..._at_gmail.com> wrote in message
> <snip>
> > I plan to take mAsterdam's advice and re-read all of the responses
> > (attempting to ignore BB's, which unfortunately can still serve to
> > drag me down personally, in spite of my attempts to push them aside).
> > I will also go back to some of quips (here) and earlier documents that
> > prompted me to ask the question. I will see if I can better
> > understand what aspects of the arguments have anything at all to do
> > with my two database navigation examples (code navigating and DBMS
> > navigating based on metadata specs and query declarations).
> >
> > My assessment to date is still that database navigation, the way I am
> > discussing it, is not the evil it might have been purported to be.
> > There is always the possibility that BB is right and I am still very
> > confused on this point, as I certainly have been in the past. Thanks
> > for your help! --dawn
>
> OK, after a bit of reading and being at only 4 out of 8 so far on the
> academy awards (but tie with the hubby so far), I tracked down one of
> the writings that has high enough regard, I suspect, but didn't
> exactly impress me on the statement regarding navigation. There must
> be better write-ups than this on why not to navigate, but this one was
> referred to from another one I re-read and is the better of the two.
>
> >From "Third-generation database system manifesto"
> ISSN:0163-5808, p.37-38 SIGMOD RECORD Vol 19 No 3 Sept 1990
>
> "The navigational point of view is well articulated in the Turing
> Award presentation by Charles Bachman. We feel that the subsequent 17
> years of history has demonstrated that this kind of interface is
> undesirable and should not be used. Here we summarize only two of the
> more important problems with navigation. First, when the programmer
> navigates to desired data in this fashion, he is replacing the
> function of the query optimizer by hand-coded lower level calls. It
> has been clearly demonstrated by history that a well-written, well-
> tuned, optimizer can almost always do better than a programmer can do
> by hand. Hence, the programmer will produce a program which has
> inferior performance. Moreover, the programmer must be considerably
> smarter to code against a more complex lower level interface.
>
> However, the real killer concerns schema evoluation. If the number of
> indexes changes of the data is reorganized to be differently
> clustered, there is no way for the navigation interface to
> automatically take advantage of such changes. Hence, if the physical
> access paths to data change, then a programmer must modify his
> program. On the other hand, a query optimizer simply produces a new
> plan which is optimized for the new environment. Moreover, if there
> is a change in the collections that are physically stored, then the
> support for views prevalent in second generation systems can be used
> to insulate the application from the change. To avoid these problems
> of schema evolution and required optimization of database access in
> each program, a user should specify the set of data elements in which
> he is interested as a query in a non-procedural language. "
>
> The authors start out with a seemingly typical statement during this
> argument that history has decided this point. Beyond this initial
> hand-waving are two arguments.

It's not right to call this "hand waving". If the authors had never addressed the question of Bachman's thesis elsewhere, you might say it's handwaving. But I believe they have thoroughly discussed this elsewhere, so they can merely state it in TTM without that being called hand waving.

Unfortunately, I can't point you to exactly where they rebutted Bachman's thesis.

I believe they are correct in saying that history has demonstrated the error of Bachman's thesis in this regard, without detracting at all from Bachman's stature as a giant among the database pioneers. Received on Mon Feb 26 2007 - 16:13:11 CET