Qpl ?

[michael]

If I am not mistaken you can still write a Qt4 application using the open source version of Qt and release it uner the QPL. My question is, as reading the license was not clear to me, can an open source application released under the QPL link to a close source library?

Thanks,
Michael

[wysota]

1. QPL only applies to X11/Free, so you can't use it for Windows or Mac development
2. You can't link to closed source libraries as you need to provide the source of all the machine-readable code you link the application with:

a. You must ensure that all recipients of machine-executable forms of these items are also able to receive and use the complete machine-readable source code to the items without any charge beyond the costs of data transfer.

So I think the bottom line is that you can link to a closed source library as long as all users can download it from a separate place (because you can't bundle it with your software), but I'm not sure of that. I think that if you make use of such library optional (meaning that your software can benefit from it but can also live without it), you can use it, just like with GPL. But this is all tricky and QPL is veeeeeeeeeeeeeeery rarely used (and in general applies to Open Source software, so ask yourself if one can consider your software Open Source).

[michael]

1. QPL only applies to X11/Free, so you can't use it for Windows or Mac development
2. You can't link to closed source libraries as you need to provide the source of all the machine-readable code you link the application with:

So I think the bottom line is that you can link to a closed source library as long as all users can download it from a separate place (because you can't bundle it with your software), but I'm not sure of that. I think that if you make use of such library optional (meaning that your software can benefit from it but can also live without it), you can use it, just like with GPL. But this is all tricky and QPL is veeeeeeeeeeeeeeery rarely used (and in general applies to Open Source software, so ask yourself if one can consider your software Open Source).

Hrmm.. Ok, thanks... So much for that idea.

[Brandybuck]

1. QPL only applies to X11/Free, so you can't use it for Windows or Mac development

Not necessarily. Since the Qt API is identical on all platforms, and you are linking to the library purely through references to the API, then the situation is not quite so clear cut. Your code doesn't suddenly become illegal because you run it on one platform rather than another.

However, both the GPL and QPL require that applications linking to the library also be Open Source. So this is not a loophole.

2. You can't link to closed source libraries as you need to provide the source of all the machine-readable code you link the application with:

It depends on what libraries they are. If they are "system" libraries that normally come with the OS or compiler, then the GPL allows an exception for them. Otherwise you couldn't write any applications under Windows, since win32 is closed source. A third party library is definitely out of the question though.

[wysota]

Not necessarily.

That's what Trolltech's note about QPL says and its their licence, so I guess they know what they are saying.

Since the Qt API is identical on all platforms, and you are linking to the library purely through references to the API, then the situation is not quite so clear cut. Your code doesn't suddenly become illegal because you run it on one platform rather than another.

You have to decide which licence applies to each code distribution. So you can release your app under QPL which links with a QPL-licenced Qt library on Linux, but you can't release your app under QPL which links with a QPL-licenced Qt library on Windows, because QPL applies only on Linux. And you can't distribute your app under QPL and link with a library under GPL, as those licences are not compatible.

[michael]

That's what Trolltech's note about QPL says and its their licence, so I guess they know what they are saying.


You have to decide which licence applies to each code distribution. So you can release your app under QPL which links with a QPL-licenced Qt library on Linux, but you can't release your app under QPL which links with a QPL-licenced Qt library on Windows, because QPL applies only on Linux. And you can't distribute your app under QPL and link with a library under GPL, as those licences are not compatible.

Yeah, well. As I am sure everyone here knows AIM upgraded their API to inlcude things like photo shareing, voice talking, etc and I wanted to writed a client for linux at the very least for my own use. Who knows, maybe for everyone else as well if it turned out good enough and no one made an AIM client for linux with all of those features by that time. But, from what I can tell it is all closed source. Blah...

Michael

[wysota]

Yeah, well. As I am sure everyone here knows AIM upgraded their API to inlcude things like photo shareing, voice talking, etc and I wanted to writed a client for linux at the very least for my own use. Who knows, maybe for everyone else as well if it turned out good enough and no one made an AIM client for linux with all of those features by that time. But, from what I can tell it is all closed source. Blah...

If you want to use an external library (is there really a version for Linux?), then it is forbidden. But if you want to write an own library which uses the same protocol to communicate, then I don't see any reason not to do it.

[michael]

It is an SDK written by AOL for Windows, Mac, and Linux.

The Mac version lacks video features and the GNU/Linux version lacks the secure connection features. Other than that most everything else is included. So it is an external library.

O-Well

[wysota]

Under what licence is it distributed? Maybe it has some special clause or its licence is GPL-compatible?