[runaway]

The first two responses to you were a solid yes and a solid no. I think that just demonstrates how the concept does not apply to application versioning.

[jjav]

It most certainly applies, the previous poster gave good examples of config files syntax and semantics, db compatibility, etc, etc.

On the UI front it really depends, you need to make decisions and let users know to avoid surprises.

At Sun the process was that every possible interface that something or someone can depend on is acknowledged to be an interface. Is GUI pixel positioning an interface? Well yes, clearly it is as someone could write tools that rely on that position.

But do you as the author want to give users an assurance that you won't break this except in major releases? Maybe not. So interfaces were classified on the axis of public/private and stable/unstable (it was a bit more complex but that's the gist). Most applications used to classify the GUI elements as an unstable interface. Then you document that so consumers of the application know they shouldn't rely on GUI elements not moving.

[runaway]

I was specifically trying to contrast programming interfaces against the large universe of applications that don’t expose any. You bring up an interesting point about external dependencies such as db, however I would say the vast majority of these applications I refer to don’t rely on users to set these up.

[lostcolony]

One of the "Yes" responses is clearly sarcastic; the other gives an "only if you promise an unchanging UI".

[runaway]

The yes I saw at the time has been deleted or edited I believe