Understanding Open Source Software Licenses

There many different Open Source software licenses out there. These licenses are created to cater to the needs of different combinations of software creators and software users. In most cases, if you are only aiming to use the Open Source software and not to modify and/or redistribute it, the terms of the licenses do not restrict you in any significant way.

Many Open Source software licenses are simply derivatives of one another. There are several well-known groups of Open Source licenses. Each group reflects a large early Open Source project that has since branched out into an entire family of related projects (similar to the growth of the ASF).

While Geronimo is licensed under the Apache 2.0 license, an understanding of the other popular Open Source licenses available is vital for putting in perspective the benefits of Geronimo’s license.

While a comprehensive list of approved Open Source licenses is available from the Open Source Initiative (www.opensource.org), the following are the Open Source licenses that are examined in this section:

• The MIT license

• The BSD license

• The new BSD license

• The GNU General Public License (GPL)

• The GNU Lesser General Public License (LGPL)

• The Apache 2.0 License

The MIT License

This is the classic public domain license. It basically allows any use of the software. It requires all distributions to include the same license. This license only protects the software creator with a “use at your own risk” disclaimer.

The goal of this license is to distribute software freely, allowing any use, yet at the same time protecting the originator from liability caused by its use.

The BSD License

This license was made famous by the early Berkeley Software Distribution (BSD) from the University of California, Berkeley.

The license adds a clause to the MIT license that requires the visible mention and acknowledgment of the source of the original software, with a statement such as, “This product includes software developed by the University of California, Berkeley and its contributors.” This is widely known as the advertising clause.

This license also explicitly restricts adopters of the software from using the name of the organization in promotion of the derived software.

The New BSD License

This is a revision of the original BSD license released in 1999, removing the need for the advertising clause and making it equivalent to the MIT license.

The original license is modified because it turns out that many Open Source software products make use of many (hundreds in some cases) other projects. To comply with the advertising clause, the derivative software often must track and print out hundreds of advertisements.

GNU’s General Public License

This is the GNU General Public License (GPL). The GNU licenses are based on copyleft (a play on the word “copyright”). Copyleft means that the license attempts to enforce that any derivative work, based on the original software, is also free software. This means that if you modify the code of copyleft-licensed Open Source software and you wish to redistribute it, you must also contribute back your modifications to the community as free software.

Copyleft licenses essentially eliminate the possibility for a commercial vendor to adopt the software, modify it, and then sell it as a proprietary solution without contributing it back as open source. The vendor, under copyleft, is obligated to contribute the modified source code as free software, under the same licensing terms.

One of the most prominent users of the GNU GPL is the Linux operating system. This is also the primary reason why all the commercial Linux vendors still make the source code of their enhanced systems publicly available.

The goal of GNU licenses is to ensure that free software stays free, protecting it and discouraging proprietary adaptation or non–Open Source redistribution of the software.

LGPL

This is the Lesser GNU Public License (LGPL), previously known as the Library license. It is a copyleft license. Originally designed for Open Source software libraries, it allows the licensed software to be linked to other software modules that may not be licensed as free software - and does not require the resulting bound unit be contributed as free software. However, many different interpretations of this license do exist.

Because of this allowance, the LGPL is considerably weaker than the GPL in the enforcement of copyleft.

Apache License 2.0

This is the software license of Geronimo, and all new ASF projects. It is a very liberal license, evolved to protect the developers and potential contributing vendors, as well as the software user.

The 2.0 license addresses the following issues:

• Reuse of the same license text by any project without the need to change wording (ASF or otherwise)

• Inclusion of the license in a source code file by reference, without fully reproducing all clauses

• Protection of the licensee (a contributor must provide a patent license if the contribution infringes on patents)

• Deletion of attribution notices (often required by the originating organization) as part of the license terms (but included in separate notice files)

Basically, the Apache licenses allow you free use of the software for any purpose, commercial or otherwise, including modification and redistribution.

However, you are obliged to include a copy of the license, and all included attributions, with every distribution of the software. You are also forbidden to use the Apache trademark for your own purposes or to suggest that ASF endorses your software in any way.

You are not, however, obliged in any way to contribute your derived software or changes to the original software.

To enable maximal software reuse between Open Source projects, however, the ASF has consciously tried to make the Apache 2.0 license compatible with GNU’s GPL. However, as of today, no legal expert is able to confirm this compatibility.

Important

The Apache License 2.0 is one of the most refined and liberal (yet vendor-friendly) Open Source software licenses in the world. The acceptance of IBM to the terms of the license (for their involvement with Geronimo) is a clear testament to the value and applicability of the license. You are in good company when adopting Open Source software with the Apache 2.0 license.

For more detailed answers to frequently asked questions regarding the Apache 2.0 license, see the FAQ (www.apache.org/foundation/licence-FAQ.html).

Interpreting the Licenses

As mentioned previously, almost all of the licenses allow you to install and use a single instance of the item for personal or commercial use without restriction. They tend to place more restriction on those who need to modify and/or redistribute the software. In case of any doubt, before extensive deployment in an enterprise, you should seek specific legal advice. Only a qualified attorney can give you appropriate legal advice on the selection of Open Source licenses for your own specific purpose.