Legal Team/Archive/license expression syntax

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Information & Background on License Expression Syntax Proposal

The following info was posted to the SPDX mailing lists on 9 April 2014:

Editor’s note: Big thanks to Mark Gisi for driving this important effort.

In the wake of a highly productive cross-functional meeting at the Linux Collaboration Summit, the SPDX Legal Team proposes certain changes to the SPDX specification and license list.

Statement of the problem:

The current SPDX Specification and License List have a limited language (i.e. and/or) that is not suitable for expressing complex license situations (for examples of such complexity, see http://wiki.spdx.org/view/FileNoticeExamples ). Additionally, the current SPDX License List currently requires the addition of multiple licenses to the list in order to capture combinations of versions, the “or later” license genre (i.e. GPL-2.0 and GPL-2.0+) and the most common exceptions (i.e. GPL-2.0+-with-autoconf-exception and GPL-3.0-with-autoconf-exception). It should be noted that the SPDX Legal Team identified more than 30 discrete exceptions. Finally, license exceptions (i.e. autoconf-exception) are generally not versioned, and therefore, accounting for changes to the license exceptions when they are part of the canonical license creates opportunity for error and confusion. For additional background please see http://wiki.spdx.org/view/Legal_Team/License_Expression_Review_1

Aim:

Improve the ability to describe more license variations utilizing some operator(s) without impact to the current timeline for the next version of the SPDX Specification.

Proposed Solution:

1) “+” to be added to the SPDX Specification as an operator to denote “or later.” As a result, all current licenses on the SPDX License List with a “Full Name” that includes “or later” will be deprecated. Deprecated means the license entry will technically remain on the list (just moved to the Deprecated section) and list users will be highly discouraged from using them. Deprecated licenses are potentially subject to removal in a future version of the list.

  • Example: The license GPL-2.0+ will be deprecated. License entry GPL-2.0 will remain on the SDPX license list and the following is still a valid license expression “GPL-2.0+”. This state’s GPL-2.0 or later because the “+” now plays the role of a unary operator that means ‘the version of this license or a later version’. The following would also be a valid license expression as well: EPL-1.0+ which means EPL-1.0 or a later version. The change of the “+” to an operator will make even more sense once one considers license exceptions (modifiers) in the next section.

2) “WITH” binary operator (similar to AND/OR) to be added to the SPDX Specification. It denotes that the license identified by the SPDX short name identifier is modified by a well-defined exception on a new “SPDX Modifier List” as described in section (3). As a result, all current licenses that include the term “exception” in the “Full Name” will be deprecated.

  • Example: “GPL-2.0-with-bison-exception” will be deprecated but the following expression, which achieves the same result, is now valid: “GPL-2.0 WITH bison-exception”.

3) The Legal Team will be responsible for creating and maintaining the canonical list of SPDX License List modifiers (i.e. “auto-conf- exception, bison-exception”). It should be noted that licenses that are deprecated will be able to be expressed (more eloquently) with the new changes; hence no license will “fall off” the SPDX License List, nor will this create a compatibility issue. URL references to all deprecated licenses will be maintained for full backward compatibility.

  • For example: the following is now a valid expression: “GPL-2.0+ WITH bison-exception” where the “+” and “WITH” operators allow a more flexible expression to be constructed. Prior to this addition this expression was not easy to express.

Longer Term Solution:

Add capability for users to define modifier references local to an SPDX document, analogously the way LicRef is used for licenses not on the License List. This will involve adding “ModRef” to the SPDX Specification so the following would be a valid expression: “GPL-2.0 WITH ModRef23.” Where ModRef23 provides the text of a license modifier that does not appear on the SPDX Modifier List. In the initial proposed solution, the way to express a file with a GPL-2.0 license with an exception, that is not included on the SPDX Modifier canonical List, will be by including the full text of the license and the exception as a single LicRef (which is the current state of affairs as well).

Rationale:

The proposed solution will provide the SPDX community the ability to express more licenses and license combinations in a more elegant and meaningful (human consumable) way then is currently available under the existing SPDX Specification and License List. To the extent that the SPDX community has come to rely on any of the licenses superseded by the new specifications those licenses will still be available on the SPDX License List (although deprecated). Finally, the initial proposed solution is a major improvement to the current situation and is easily extensible to the even more flexible longer term solution without impacting the current timeline for SPDX 2.0.