Re: Coupling or not coupling database and GUI libraries (was: GWindows and a future home for it)

[Ludovic Brenta <ludovic.brenta@insalien.org>]

As a backgrounder on my experience: a few years ago, I wrote a 120
kSLOC application in Java that did just that - an interface to a
database.  The front-end started as Swing but changed to HTML and a
bit of Javascript.  There was an abstraction layer over the database
that supported Oracle, DB2 and DB2/400 and provided the database
schema metadata to the visualisation layer.  There were a connection
pool, several caches of metadata and data, and application-level
permission settings (authentication was delegated to the database
server, authorisation done in the application).

I have several concerns with tight integration of GUI and database
libraries.

1. If every widget can be attached to a database query, will every
   update to a widget not cause an SQL query?  This should be avoided.

2. If every widget is attached to a query, is it possible to update
   several widgets with one query, i.e. that several widgets be
   attached to the same query?

3. Is it possible to perform arbitrarily complex, application-specific
   formatting to the data as it goes back and forth between the
   widgets and the database?

In the application I mentioned, we would routinely do queries that
joined 5 or 6 tables, and we had lots of heuristics to help speed that
up.  In one of the screens, we would present a tree structure
constructed from oh, perhaps 10 different queries.

I have not really had a deep look at either Delphi, MFC, or GWindows,
but I suspect that coupling the GUI and the database libraries is only
useful for quick-and-dirty work when you want to create forms where
one form=one record in the database.

But for anything more complex, such coupling just gets in the way.  In
fact, it is the job of any non-trivial database GUI to perform the
"grunt work" you mentioned, and I cannot think of a useful way the
library could ease that.  Or perhaps you were only thinking of
marshalling and unmarshalling of individual database fields to and
from the database?  Yes, this is grunt work, but it is often
application-dependent too.  And unlike Java, Ada has generics which
can be instrumental in making this grunt work a piece of cake.

Java's JDBC is not tightly coupled with Swing or AWT.  Both APQ and
GNADE are similar in concept to it, or the ODBC API which is also not
coupled with any GUI.

I do not think it is wise to have a GUI-dependent database library.

-- 
Ludovic Brenta.