Well, whatever, man. I've seen applications developed in 4GL, not a pretty sight.
I've seen ugly applications in every language I've ever worked with. That's normally down to unrealistic schedules, 'fast' programmers and the resulting Big Ball of Mud. The language isn't often to blame.
Since most modern applications are build in tiers .
Like modern Progress applications.
there's usually no problem to replace the database stuff. By not building your application in a database you'll still have the option to change databases in the future.
That's true, but there is the tradeoff in using Progress: lack of portability of 4GL code (although there's always DataServers), because of the inferior SQL industry standard, against great business side development productivity. You pays your money...
You're not tied to a proprietary system with a proprietary language.
You're always tied to an extent, particularly with your GUI choices, as they will always change the most against a well designed business and database side.
You program in VB5, then along comes Visual Fred. You develop in Delphi and Borland goes under. There are no guarantees in this business.
One of the most exasperating things for me about Progress is it's determination to remain backwards compatible to the most primitive front end versions.
Many people however, see this as a good thing, one of the strongest arguments in favour of Progress. Presumably you must too.
The minor differences in SQL between different databases are easily isolated to a single file.
Not if you use any SQL 'enhancement', T-SQL, PL-SQL, etc.
Besides, during the development of our system we didn't have to pay a penny for MySQL, now that we're using it we obviously pay for the two server licences we need, but they are an awful lot cheaper than the ones for Progress.
Now that's something we can agree on.