I'm working on a calendar project, on my own. In this project I've to use Swiss Ephemeris. It is licensed under GPLv2 and commercial. With commercial version of license, developers entitled to distribute the software, as his/her wish. But as this is my personal project, I've to use the GPLv2 license.By using the library and data file, I'm generating data for calendars. In future I shall publish these calendars in a website, freely. In this process obviously I've to modify the library, write some of my own code and other chores. Will I've to make my final source code open. I don't have any problem to make this public. But I'm asking, if I've to.Edit: From the detailed answer from @apsillers & others, it is clear to me that, I'll not have to make my software GPL or even give source code to the visitors to the website. Though I've to make my displayed data GPL by the clause, as the Swiss Ephemeris data, licensed under GPLv2 or later and commercial:More generally, when a program translates its input into some other form, the copyright status of the output inherits that of the input it was generated from.
Do I have to make source code open, if I use GPLv2 licensed software to derive data
licensing;open source;gpl;source code
Since you're making a derivative work of GPL-licensed software, your combined work would need to be licensed under the GPL as a whole. However, if you don't want to distribute your work, you are in no way compelled to shared your changes.The GPL FAQ has this to say on keeping your modifications private:Does the GPL require that source code of modified versions be posted to the public?The GPL does not require you to release your modified version, or any part of it. You are free to make modifications and use them privately, without ever releasing them...But if you release the modified version to the public in some way, the GPL requires you to make the modified source code available to the program's users, under the GPL.Thus, the GPL gives permission to release the modified program in certain ways, and not in other ways; but the decision of whether to release it is up to you.Thus, you are not required to make your modified program public, but you if you do, you must share it under the GPL.Perhaps you're also worried that sharing your output calendars will compel you to share your modified code. The FAQ explains that output data produced by a GPL-licensed work is not covered by the GPL, unless the output actually contains GPL-licensed material (e.g., if part of the GPL-licensed program itself is included in the program's output):Is there some way that I can GPL the output people get from use of my program? For example, if my program is used to develop hardware designs, can I require that these designs must be free?In general this is legally impossible; copyright law does not give you any say in the use of the output people make from their data using your program. If the user uses your program to enter or convert his own data, the copyright on the output belongs to him, not you. More generally, when a program translates its input into some other form, the copyright status of the output inherits that of the input it was generated from.So the only way you have a say in the use of the output is if substantial parts of the output are copied (more or less) from text in your program. For instance, part of the output of Bison (see above) would be covered by the GNU GPL, if we had not made an exception in this specific case.In what cases is the output of a GPL program covered by the GPL too?Only when the program copies part of itself into the output.So, your output is probably not GPL-licensed. Note that even in some unusual case where the output is somehow GPL-licensed (like a Bison grammar), the output is a separate work from the program that created it. You'd need to obey GPL restrictions on the output, but sharing GPL-licensed output does not mean you must share changes on the GPL-licnesed program that created that output. The GPL on the program only comes into effect when the program itself is distributed, not when its output is distributed.