The compatibility mechanism in the CC ShareAlike licenses allows contributions to an adaptation to be licensed under a different license if “approved by Creative Commons as essentially the equivalent of this Public License” and listed on the Compatible Licenses page.<ref> Note that the BY-NC-SA license did not contain a compatibility mechanism in versions prior to 4.0. The mechanism is contained in both BY-SA and BY-NC-SA as of version 4.0.</ref>
As steward of the CC licenses, we think it is important to ensure that licensors can trust that when they license their works under one of our licenses, the features of our licenses that are important to them continue to be respected when their works are adapted. Creative Commons seeks to meet licensor expectations as closely as possible, but we also seek to grow the commons of remixable content by declaring compatibility with other licenses that share the same fundamental purpose and effect as our licenses. Please keep these considerations in mind as you review the process and criteria below. Learn more about how ShareAlike compatibility works here.
Creative Commons may revise this document in the future, with a 30-day public consultation before any changes are made final.
1. A proposal for a candidate license is made to Creative Commons via a posting to the CC license development and versioning list.
The proposal must include a link to the full text of the license posted by the steward.<ref> CC may require additional information in connection with the proposal, such as identification of the important license features. </ref> It is not essential that the proposal be made by the license steward (see process note, below), but it is strongly preferred. CC may also begin the process by proposing a candidate license. Similar licenses containing substantially the same text may be proposed or analyzed together.
2. Creative Commons creates a wiki page for the candidate license.
The primary place of public discussion will be the CC license development and versioning list; however, relevant information about the proposal, a summary of the points of discussion, and analysis of whether compatibility criteria are met will be posted on the wiki.
3. Creative Commons publishes a preliminary comparison and analysis of the CC license and the candidate license.
This comparison maps elements and features of the CC license to elements and features of the candidate license, and analyzes relevant differences.
4. The public discussion period begins.
The public discussion period will typically remain open for 30 days. If complicated issues arise, it may be desirable for the discussion to last longer than 30 days until issues are understood fully. However, Creative Commons also reserves the right to close the public discussion early if we determine that a candidate license clearly does not meet our criteria for compatibility.
5. CC issues a compatibility determination.
Creative Commons will issue a determination detailing reasons why a candidate license is or is not compatible with the CC license. The decision will be posted to the CC license development and versioning list, and posted on the wiki page.
If compatibility is declared, Creative Commons will list the license as a compatible license on its compatible licenses page. Reusers of works under the relevant CC license may thereafter apply the compatible license to the contributions they make to adaptations of those works. If CC declines to name the license as compatible, Creative Commons will list the candidate license as reviewed but not deemed compatible on its compatible licenses page. The candidate license will not be reconsidered for compatibility unless the license steward addresses the identified concerns.
This is not intended as an approval process or a recommendation process.
We encourage participation of license stewards.
To be compatible with BY-SA or BY-NC-SA, a candidate license must have the same purpose, meaning, and effect as the corresponding CC license.<ref> This requirement was originally dictated by the language in BY-SA 3.0, and was carried forward in BY-SA 4.0 and BY-NC-SA 4.0.</ref> For each of the criteria below, it is not necessary that the candidate license provide identical treatment. As long as the treatment of relevant factors in the candidate license closely approximates the treatment in the CC license then compatibility is achievable. This is not an exhaustive list of criteria. CC retains discretion not to declare a license compatible based on other factors.
Technical note about adaptations of CC-licensed material.
When an adaptation of a CC-licensed work is created, use of the adaptation requires compliance with the original CC license and the license applied by the adapter to contributions she makes to an adaptation. This means the licenses “stack” in the sense that users of the adaptation need to be aware of and comply with the terms of the original license and the adapter’s license.<ref>However, starting with the version 4.0 ShareAlike licenses, it is explicitly clear that downstream users of adaptations created from 4.0 licensed works may satisfy the terms of the upstream license(s) – version 4.0 – by complying with the conditions of the adapter’s license. That means, for example, that someone using the adaptation may attribute the original author in the manner prescribed by the adapter’s license (i.e. the compatible license) rather than the manner dictated by the version 4.0 license applied to the original.</ref> For this reason, the conditions of compatible licenses must align closely with the corresponding CC license. This best respects the expectations of the original CC licensor, and comports with the expectations and practices of reusers of adapted works.