Why Google chose the Apache Software License over GPLv2 for Android

关于解释为什么Google采用Apache License的文章，希望以后翻译出来。

Google finally entered the mobile software market by turning the 2005 acquisition of Android into the Open Handset Alliance. Google hopes to promote third-party mobile software development and foster a broad developer community on top of Android's Linux-based mobile platform. In the wake of Google's announcement, one topic that has been discussed by some members of the open-source software community is the significance of Google's licensing choice.

Although the underlying Linux kernel is licensed under version 2 of the Free Software Foundation's General Public License (GPLv2), much of the user-space software infrastructure that will make up the Open Handset Alliance's platform will be distributed under version 2 of the Apache Software License (ASL). This raises certain questions about Google's goals in the mobile space and the nature of the third-party application ecosystem that will emerge around the platform.

ASL, which is widely used in the open-source software community and has been approved by the Open Source Initiative, is a permissive license that is conducive to commercial development and proprietary redistribution. Code that is distributed under the ASL and other permissive licenses can be integrated into closed-source proprietary products and redistributed under a broad variety of other terms. Unlike permissive open-source licenses, "copyleft" licenses (such as the GPL) generally impose restrictions on redistribution of code in order to ensure that modifications and derivatives are kept open and distributed under similar terms.

Permissive licenses like the ASL and BSD license are preferred by many companies because such licenses make it possible to use open-source software code without having to turn proprietary enhancements back over to the open source software community. These licenses encourage commercial adoption of open-source software because they make it possible for companies to profit from investing in enhancements made to existing open-source software solutions. That potential for proprietary investment on top of an open stack is most likely what inspired Google to adopt the Apache Software License for its mobile platform. Availability of Android under the ASL will ensure that a broader number of companies will be able to adopt the platform and build on top of it without having to expose the inner workings of proprietary technologies that give them a competitive advantage.

Although using a permissive license like ASL is the best way to build support for the Android platform, critics argue that Google has sacrificed an opportunity to encourage greater openness in the broader mobile software space. If Android was distributed under the GPLv2, companies building on top of the platform would have to share their enhancements, which could theoretically lead to widespread sharing of code and a more rapid acceleration of mobile software development.

The counterargument is that distributing Android under a copyleft license could potentially limit the evolution of the mobile software ecosystem by discouraging commercial development on top of the platform. Proprietary mobile software development companies that integrate Android into their technologies would have to dramatically change their business models if they aren't given the ability to keep their enhancements proprietary.

It is important to note that the ASL is only being applied to the assortment of user-space platform components that make up Android. The kernel itself is still licensed under the GPLv2, and third-party software that runs on top of the platform can be distributed under pretty much any license, including commercial and copyleft licenses. It is also important to note that, although the ASL was not compatible with previous versions of the GPL, it is entirely compatible with the GPLv3. This means that code distributed under the ASL can be incorporated into GPLv3 software. As a result, developers can choose to distribute Android derivatives under the GPLv3 in order to ensure that further development on top of their own enhancements remains open.

Ultimately, the decision to use the ASL is sensible. Although it would be beneficial to all if Google were to use Android licensing to further open the market, that likely would have stifled adoption of the platform by handset makers. When it comes right down to it, the handset makers are the developers who are most significantly affected by the Android license, since they are the primary distributors of mobile phone platforms. The ASL will allow individual handset makers to develop proprietary customizations for the platform as needed to accommodate the unique technologies in their individual products. Third-party software developers who are building applications on top of Android will largely be unaffected by Google's licensing decision since the individual applications can be distributed under their own licenses. Another point worth noting is that Linux-based mobile platforms created by other mobile technology coalitions like the LiMo Foundation also facilitate mixing proprietary and open software.

As more details emerge and more source code becomes available, it's likely that third-party developers and handset makers will eagerly flock to Android in order to benefit from the ecosystem that Google is creating.

来源：http://arstechnica.com/uncategorized/2007/11/why-google-chose-the-apache-software-license-over-gplv2/