多重授權

多重授權是一種在不同的授權條款下釋出同一個軟體的方式。軟體發行方通常採用兩個或以上的授權條款，或授權集。

當一個軟體採用多重授權時，接收者可以選擇他們願意遵守的授權釋出衍生品。但軟體套件或庫中存在多個授權條款並不意味著接受者可以任選其一。在某些情況下，例如如軟體套件中有多個以不同授權條款釋出的軟體，則接收者必須遵守所有授權條款的條款。多重授權兩個常見用途是解決授權條款相容性^[1]和開源軟體商業化。^[2]

商業模式

對於商業公司而言，多重授權通常用於支援自由軟體的商業化。這種情況下，軟體會採用兩種授權：專有軟體授權條款（允許建立專有應用程式）和Copyleft 自由軟體/開源授權條款，軟體通常以極低的價格或免費提供社群版本，並通過向商業機構出售專有授權條款來獲利。這種模式與共享軟體相似。

在大多數情況下，只有著作權所有者才能更改授權，因此通常只有完全擁有軟體著作權的公司才會採用多重授權。若非公司職員為軟體增添了新代碼，並以更寬鬆的授權釋出它，可能會導致衝突：公司並不擁有新增代碼的著作權，不能修改代碼的授權，因此無法合法地將其合入軟體本體中。多數公司會要求社群貢獻者提交代碼前簽署貢獻者協定，以避免上述問題。 ^[3]

自由軟體公司可以使用多重授權來提供不同的服務。例如，可以為企業級使用者提供個性化服務、提前釋出穩定版、授予釋出專有作品的權利，同時向所有人提供開源的免費版。這樣，軟體可以受到來自開源社群使用者、駭客的貢獻，這些貢獻可以是修改原始碼、提升口碑、對專有授權使用者的支援等。但是，若不尊重開源社群的貢獻，如在授權條款中增設不平等條款^[4]、涉嫌竊取開源社群成果^[5]等，則可能失去支援。

採用多重授權的軟體套件括NetBeans IDE 、MySQL、 Asterisk 、Berkeley DB 、 Modelio 、Ice 、 Magnolia CMS 、 JUCE 、 wolfSSL ^[6]和Qt開發工具包等。

多重授權的一個典型例子是MySQL。Oracle MySQL 有多個版本，MySQL 企業版^[7]、MySQL 標準版、MySQL Cluster 運營商級版需要付費，以每月訂閱形式提供授權。其他版本，如 MySQL 經典版、MySQL 社群版等，則可以免費使用，但有一些限制（採用GPL協定、僅提供社群支援等）。 ^[8]

授權條款相容性

多重授權可以保證授權條款相容性 ^[1]，即允許使用者選擇不同授權條款，合併不同自由軟體的原始碼，繞過授權條款衝突問題。

舉例：

Mozilla早期開發的軟體，如Mozilla應用套件、早期的Firefox和Thunderbird等，均採用三重授權分發原始碼，分別為Mozilla公眾授權條款（MPL）1.1、GNU通用公眾授權條款（GPL）2.0和GNU較寬鬆公共許可證（LGPL）2.1^[9]。後續MPL 2.1修改了部分條款，使之與GPL相容，不再需要使用三重授權。^[10]
Perl採用GPL、藝術授權條款雙重授權。^[11]
Ruby的授權條款明確包含了對GPL的雙重授權。

參考來源

^ ^1.0 ^1.1 Nikolai Bezroukov. Comparative merits of GPL, BSD and Artistic licences (Critique of Viral Nature of GPL v.2 - or In Defense of Dual Licensing Idea). 2001. （原始內容存檔於2001-12-22）. Viral property stimulates proliferation of licenses and contributes to the "GPL-enforced nightmare" -- a situation when many other licenses are logically incompatible with the GPL and make life unnecessary difficult for developers working in the Linux environment (KDE is a good example here, Python is a less known example).
^ Licensing in a Post Copyright World. 2013-07-23. The AGPLv3 was a terrible success, especially among the startup community that found the perfect base license to make dual licensing with a commercial license feasible. MongoDB, RethinkDB, OpenERP, SugarCRM as well as WURFL all now utilize the AGPLv3 as a vehicle for dual commercial licensing. The AGPLv3 makes that generally easy to accomplish as the original copyright author has the rights to make a commercial license possible but nobody who receives the sourcecode itself through the APLv3 inherits that right. I am not sure if that was the intended use of the license, but that's at least what it's definitely being used for now.
^ Digium Incorporated. Asterisk Guidelines, The contributor license agreement. [2009-02-10].
^ 关于 Netscape 公共许可证. GNU.
^ 苹果许可证（APSL）1.1版本的问题.
^ wolfSSL Embedded SSL/TLS Library | Now Supporting TLS 1.3. [2020-01-27] （美國英語）.
^ My SQL Enterprise Edition. Oracle. [25 April 2013].
^ MySQL Community Edition. Oracle, MySQL. [25 April 2013].
^ Mozilla Foundation. Mozilla Code Licensing. [2007-09-17].
^ MPL 2 Upgrade. [2012-08-18].
^ The Perl Foundation. Perl Licensing - perl.org. [2007-09-17].

外部連結

Dual Licensing information from OSS Watch（英語：OSS Watch）
Article "Does dual licensing threaten free software?" by Glyn Moody
Article "The Dual-Licensing Model" by Don Marti
Article "Dual Licensing: Having Your Cake and Eating It Too" by Philip H. Albert
Article "Dual-Licensing Open Source Business Models" by Heather Meeker
Article "How to use open source as a power marketing tool" by John Koenig
Paper "Dual Licensing in Open Source Software Industry" by Mikko Välimäki
Dual Licensing Schemes
"Should code be 「dual licensed」 under the GPL and a permissive license?" by Software Freedom Law Center
Combining GPL, closed code. [2013-01-03]. （原始內容存檔於2013-01-03）.

這是一篇與軟體相關的小作品。您可以透過編輯或修訂擴充其內容。

[GPLviral-1] 1.0 ^1.1 Nikolai Bezroukov. Comparative merits of GPL, BSD and Artistic licences (Critique of Viral Nature of GPL v.2 - or In Defense of Dual Licensing Idea). 2001. （原始內容存檔於2001-12-22）. Viral property stimulates proliferation of licenses and contributes to the "GPL-enforced nightmare" -- a situation when many other licenses are logically incompatible with the GPL and make life unnecessary difficult for developers working in the Linux environment (KDE is a good example here, Python is a less known example).

[2] Licensing in a Post Copyright World. 2013-07-23. The AGPLv3 was a terrible success, especially among the startup community that found the perfect base license to make dual licensing with a commercial license feasible. MongoDB, RethinkDB, OpenERP, SugarCRM as well as WURFL all now utilize the AGPLv3 as a vehicle for dual commercial licensing. The AGPLv3 makes that generally easy to accomplish as the original copyright author has the rights to make a commercial license possible but nobody who receives the sourcecode itself through the APLv3 inherits that right. I am not sure if that was the intended use of the license, but that's at least what it's definitely being used for now.

[3] Digium Incorporated. Asterisk Guidelines, The contributor license agreement. [2009-02-10].

[4] 关于 Netscape 公共许可证. GNU.

[5] 苹果许可证（APSL）1.1版本的问题.

[6] wolfSSL Embedded SSL/TLS Library | Now Supporting TLS 1.3. [2020-01-27] （美國英語）.

[7] My SQL Enterprise Edition. Oracle. [25 April 2013].

[8] MySQL Community Edition. Oracle, MySQL. [25 April 2013].

[9] Mozilla Foundation. Mozilla Code Licensing. [2007-09-17].

[10] MPL 2 Upgrade. [2012-08-18].

[11] The Perl Foundation. Perl Licensing - perl.org. [2007-09-17].

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