On Sun, 26 Feb 2006 08:10:36 -0600 Jon S. Berndt wrote: > Chris Metzler wrote: >>> >>> Sorry, I'm feeling really slow (probably because it's late where I >>> am, > and >>> I should go to sleep). There was a change in JSBSim configuration >>> file format in going to JSBSim 2.0; that has caused a lot of >>> aircraft that haven't yet been updated to not run under FG 0.9.9, >>> and still others that *have* been updated to not run under earlier >>> versions (although one can always hang on to an old version, I >>> guess). But as you note >>> >>> The reason I'm looking at this is because you described FG as "not >>> maintaining backward compatibility"; for the most part, I don't think >>> that's fair to FG. I agree that the JSBSim config file change is an >>> example of failing to maintain backward compatibility; but I'd claim >>> that it's not breaking backward compatibility in the way you >>> describe. > > > Well ... this is interesting. Somehow I missed this conversation until > now.
Probably because you were being smart and sleeping, unlike me!
> For the past year and more I have gone to great lengths to publicize the
> impending changes to JSBSim in this mailing list, the JSBSim mailing
> list, and the JSBSim newsletter. I've publicized the backward
> incompatibility, and the reasons for going to the new format. I've
> publicized that we have created a converter for going from the old
> format to the new.
I agree.
> We did not "fail to maintain backward compatibility" so much as we did
> not *limit* ourselves by the past.
This sentence, though, I wouldn't necessarily agree with. See below:
> This is not the first time there has
> been a major configuration file format change. Likely, it *will* be the
> last. Originally, eight years ago, the JSBSim configuration files were
> not rooted in XML, but were simply in a text format. We moved to XML
> somewhere about 2000. Some newer technologies (to me, anyhow) emerged,
> an industry standard began to emerge (that JSBSim helped to inspire),
> and some new and broad JSBSim capabilities were being added - all which
> dictated that there would need to be changes in the way the config
> files were arranged. This has all been communicated both here and in
> the JSBSim mailing list. Maintaining backward compatibility would have
> negated what we were hoping to accomplish - one of which was better
> formed XML config files and offloading JSBSim from much of the file
> parsing work by using the eXpat-based easyXML for our XML parser.
To what little I understand, I agree completely that changes were
good. But from the FlightGear perspective, one could have imagined
different ways of dealing with old-style config files. For example, one
could have imagined a parser which detected the config file style, and
acted differently on that basis -- anywhere from screaming about the old
file's format and warning that it'll probably stop working with the next
version, to encouraging the user to look into getting an updated config,
to pointing the user to the conversion software so they can try it
themselves, to having the user stand by while config file style conversion
was attempted right then in an automated fashion -- all things I've seen
other applications do when faced with this situation. We just broke the
old files, and while that should nudge developers who hadn't yet
reacted to the warnings about the config file changes, it also was
probably rough on a few users, who found that planes they enjoyed suddenly
didn't work anymore.
Don't get me wrong -- I'm not even really saying that you or anyone
else *should* have put the time into making one of the above possibilities
happen. I think the old stuff could have been handled differently; but
I do know that everyone has limited time and the time spent on that
would have been time not spent on other things; and to be selfish about
it, the problems it's caused with some older a/c haven't bitten me,
because I don't fly those a/c, so I haven't much noticed. I'm not being
critical about how things were done. I just do think it's fair to call
it "breaking backward compatibility": old stuff doesn't work anymore.
I'm not saying that's a bad thing; I'm just saying that it's true.
> Remember, were are not yet at v1.0. I wanted to make sure that we "got
> it right" for v1.0. There are many new capabilities that we really
> wanted to have. We spent a long time developing it and testing it. Some
> last minute adjustments presented some glitches with the config file in
> FlightGear, but those will soon be a thing of the past, and we'll be
> dealing with a more stable, more capable, JSBSim.
No worries from me.
-c
--
Chris Metzler [EMAIL PROTECTED]
(remove "snip-me." to email)
"As a child I understood how to give; I have forgotten this grace since I
have become civilized." - Chief Luther Standing Bear
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