Clarification/license change from Apache 2.0 to LGPLv3

[RalphSteinhagen]

Wider Chart-FX goals

We are happy that Chart-fx is being used as a charting library in other laboratories, academia, industries, and JavaFX enthusiasts. Built upon JavaFX it has been primarily a publically-funded development by GSI for FAIR, an accelerator-based research facility presently constructed nearby Darmstadt, Germany. We initially decided to open it and its development to other partnering laboratories as well as to the general public. This is in-line with sharing, accepting external feedback and improvements, to contribute to the common JavaFX ecosystem, as well as to support the public common good as (see e.g. Public Money - Public Code).

Change

Upgrade this library license to LGPLv3. This specifically covers the 'chartfx-dataset', 'chartfx-math' and 'chartfx-chart' sub-modules.

Free commercial and non-commercial use (as before)

Notably, the LGPLv3 permits to use this library by free open-source as well as proprietary (closed-source) software, provided you

• permit all users to exchange the library with other API-compatible library versions (e.g. those with security- & bug-fixes)
• make modifications and improvements to the library publicly available
  (ie. 'we will continue to share our improvements to the library and kindly ask you to do the same'), and
• do not change the nature of this share-alike agreement (ie. preserve the LGPLv3).

Motivation

We believe this to be a non-issue for Java developers already using and developing using JavaFX which is similarly based upon the older 'GPLv2' with 'GNU CLASSPATH exception clause' which is an (albeit weak) copyleft license which, for example, the present 'Apache 2.0' license does not fully acknowledge which may give erroneously a false sense that this library lifts these requirements and that it would grant more (or less) rights to users and developers than there are actually are. We believe that the change to LGPLv3 makes this a bit more transparent since there are more resources on that license than on the more complicated 'GPLv2 + CP exception'.

The primary motivation for this change is thus (we are not lawyers but like to keep it pragmatically KISS):

• clarify the situation and avoid being (accidentally) in conflict with other licenses being used in the library, thus
• to simplify the license dependencies and heterogeneity to one 'simple', well-known and compatible license,
• to dispel any perceived restrictions that may limit the users' freedom to run, copy, distribute, study, change and improve this library (notably if necessary for maintenance purposes) now and in the future, while
• affirming that it remains free & open-source and to entice (but not force!) others to do the same.

Please let us know if you have feedback on this, notably if you already use this library in a public/non-public context and would like to contribute and/or advertise your use of it.