Re: Request for new function in view update

Hi Yugo

Thank you for taking a look at the paper.

The key difference from PostgreSQL is that it only allows updates on single
table views. My paper discusses two kinds of joins of two tables. It
discusses how to update them and how to determine when they occur.

The paper also discusses unioning two tables. I've done work on table
intersection and table difference too, but didn't include it in the paper.

Terry Brennan

On Wed, Jun 28, 2023 at 2:49 AM Yugo NAGATA <nagata(at)sraoss(dot)co(dot)jp> wrote:

> On Thu, 1 Jun 2023 12:18:47 -0500
> Terry Brennan <terryjbrennan(at)gmail(dot)com> wrote:
>
> > Hello all,
> >
> > I am a researcher in databases who would like to suggest a new
> function. I
> > am writing to you because you have an active developer community. Your
> > website said that suggestions for new functions should go to this mailing
> > list. If there is another mailing list you prefer, please let me know.
> >
> > My research is in updating views -- the problem of translating an update
> in
> > a view to an update to a set of underlying base tables. This problem has
> > been partially solved for many years, including in PostgreSQL, but a
> > complete solution hasn't been found.
> >
> > Views are useful for data independence; if users only access data through
> > views, then underlying databases can change without user programs. Data
> > independence requires an automatic solution to the view update problem.
> >
> > In my research, I went back to the initial papers about the problem. The
> > most promising approach was the "constant complement" approach. It
> starts
> > from the idea that a view shows only part of the information in a
> database,
> > and that view updates should never change the part of the database that
> > isn't exposed in the view. (The "complement" is the unexposed part, and
> > "constant" means that a view update shouldn't change the complement.)
> The
> > "constant complement" constraint is intuitive, that a view update
> shouldn't
> > have side effects on information not available through the view.
> >
> > A seminal paper showed that defining a complement is enough, because each
> > complement of a view creates a unique view update. Unfortunately, there
> > are limitations. Views have multiple complements, and no unique minimal
> > complement exists. Because of this limitation and other practical
> > difficulties, the constant complement approach was abandoned.
> >
> > I used a theorem in this initial paper that other researchers didn't use,
> > that shows the inverse. An update method defines a unique complement. I
> > used the two theorems as a saw's upstroke and downstroke to devise view
> > update methods for several relational operators. Unlike other
> approaches,
> > these methods have a solid mathematical foundation.
> >
> > Some relational operators are easy (selection), others are hard
> > (projection); some have several valid update methods that can be used
> > interchangeably (union) and some can have several valid update methods
> that
> > reflect different semantics (joins). For joins, I found clues in the
> > database that can determine which update method to use. I address the
> > other relational operators, but not in the attached paper
> > .
> > I also discuss the problem of when views can't have updates, and possible
> > reasons why.
> >
> > I have attached my arXiv paper. I would appreciate anyone's interest in
> > this topic.
>
> I'm interested in the view update problem because we have some works on
> this topic [1][2].
>
> I read your paper. Although I don't understand the theoretical part enough,
> I found your proposal methods to update views as for several relational
> operators.
>
> The method for updating selection views seems same as the way of
> automatically
> updatable views in the current PostgreSQL, that is, deleting/updating rows
> in
> a view results in deletes/updates for corresponding rows in the base table.
> Inserting rows that is not compliant to the view is checked and prevented
> if
> the view is defined with WITH CHECK OPTION.
>
> However, the proposed method for projection is that a column not contained
> in the view is updated to NULL when a row is deleted. I think it is not
> desirable to use NULL in a such special purpose, and above all, this is
> different the current PostgreSQL behavior, so I wonder it would not
> accepted
> to change it. I think it would be same for the method for JOIN that uses
> NULL
> for the special use.
>
> I think it would be nice to extend view updatability of PostgreSQL because
> the SQL standard allows more than the current limited support. In this
> case,
> I wonder we should follow SQL:1999 or later, and maybe this would be
> somehow
> compatible to the spec in Oracle.
>
> [1] https://dl.acm.org/doi/10.1145/3164541.3164584
> [2] https://www.pgcon.org/2017/schedule/events/1074.en.html
>
> Regards,
> Yugo Nagata
>
> > Yours
> > Terry Brennan
>
>
> --
> Yugo NAGATA <nagata(at)sraoss(dot)co(dot)jp>
>