A combined application or work is often implemented by linking various components. From the end user point of view, the application may look like a single program (it may have a single name, unique interface, documentation etc.). From the developer point of view, each component is a separate program, possibly obtained under various primary licenses.

In case these various licenses are “free / open source” and “copyleft”, what kind of linking could you implement to be legally authorised to distribute the application, under a single license or – possibly – under several licenses?

There are two main cases of linking:

• Static linking combines components through compilation, copying them into the target application and producing a merged object file that is a stand-alone executable.

• Dynamic linking uses components at the time the application is loaded (load time) or during execution (run time).

In the above Matrix, we assume that both linking are permitted in two cases: when incorporation (merging codes in a “cut-paste” sense) is authorised and when the distribution of object code under the EUPL is authorised (because this covers static linking at object code level as well).

From the legal (copyright) point of view, the question of linking is similar to the incorporation discussion: does linking produce a derivative of the used components, or not?

• If the answer is “NO”, each part of the application can be licensed under its primary license: You may declare “My application is licensed to you under the EUPL, except component X that is licensed under GPL, component Y that is licensed under the EPL, component Z under the MPL etc...

• If the answer is “YES”, the distribution of the new derivative could be legally impossible (under any license) as soon a copyleft conflict exists. Such prohibition may be considered as beneficial (or protective) for the free software world in case the licensor planned to use a proprietary license. On the contrary, the prohibition may look cumbersome and fussy when all relevant licenses are OSI-approved (providing the same freedoms) and copyleft (protecting against appropriation).

More info athttp://joinup.ec.europa.eu/software/page/eupl/eupl-compatible-open-source-licences#section-3