In the Public Domain

We should first look at one of the most widely used terms in open source distribution that has not yet been certified by the Open Source Institute: placing the work "in the public domain." A work placed in the public domain has the same legal status as one for which the legal copyright term (usually 50 years after the death of all the authors) has elapsed. This condition is particularly interesting because the rights to use and profit from the work (execute, copy, and distribute the software) can be exercised by anyone, yet the ultimate right of disposing of the work (the right to authorize or restrict other's rights to it) belongs to no one and, therefore, cannot be exercised.

Software placed in the public domain essentially follows the same copyright law as the works of long-dead literary and musical authors. You can perform (execute) the works of Shakespeare, copy them, and distribute them, but remember that derivative works, compilations, and specific performances can have their own lawful copyright owners. You can include public domain software in your own work, modify it, copy it, and talk about it in publications and at conferences. You can't do the same with someone else's work, however, just because it happens to use or contain public domain work. You're otherwise free to derive any profits from public domain software.

Public domain software is unique in that it is the only form of work whose disposal rights are not retained by anyone. Every form of software licensing reserves rights 5, 6, and 7 for some entity, including the right to license work under a different scheme whenever desired. From a business perspective, it's guaranteed that legal claims of copyright violation can not be brought against users of software that is in the public domain.

The least restrictive licensing

Software licensing schemes always reserve the right to dispose of the work (grant, restrict, transfer, and license the rights). This is redundant because licensing can only exist if someone holds those basic rights, unlike work placed in the public domain. All open source licenses have that element in common, but differ in the other rights they grant or restrict.

The least restrictive form of software licensing is that which reserves only the right to disposition. The BSD and MIT licenses, for example, grant ample rights of use, creation of derivative works, and redistribution (as long as the right to dispose of the work is explicitly reserved to the original authors). Included is the right to make different licensing arrangements with whomever the licensee sees fit. The Artistic (Perl) license is somewhat less clear in its section 3, which addresses copying and modification of the original "package," but does not talk about distribution.

Tightening the reins

Most frequently, open source licenses grant ample rights for use of the software and creation of derivative works, but restrict distribution in some important way. The four most common restrictions on distribution are:

• You may only distribute the software and the modifications within your company or institution (an aspect the Artistic License).
• You may only distribute the software and the modifications in object (compiled) form as long as some value-added is provided (the XML4J commercial license).
• You may only distribute the software and the modifications for free (Artistic License).
• You must provide the source to all your modifications, or otherwise guarantee that users of your software can get hold of the source free of charge (the GPL).

These restrictions mainly affect how you profit from the intellectual property. The only restrictions made by the controversial GPL are restrictions on distribution.

Normally, these kinds of licenses don't place restrictions on the work created with the software, which gives such licenses a broad range of uses. This applies to end-user applications -- such as word processors and spreadsheets -- and to most of the tools used in software development, even commercial ones like compilers, libraries, editors, and text manipulation and make tools.

Some other licenses place absolute restrictions on distribution in order to avoid so-called "forking." As a result, most of the enhancements end up in the primary source base. But other licenses restrict distribution just to maintain control over the software. I've known only a few licenses that do this.

The most restrictive licenses

Paradoxically, one of the most restrictive licenses -- the GPL -- is very liberal about redistribution rights. Under the GPL, you can distribute the original work or its derivatives to whomever you like, as long as you make readily available the source to the original work, the modifications you obtained, and any modifications you made. Any licenses you give must also follow the GPL restrictions.

Many source code licenses restrict the use that can be made of the software. Such is the case with the Java Community Source License, which appears to restrict free use to research. Other uses require that compatibility tests be made and royalties be paid. Other licenses, like the XML4J Evaluation License, restrict the use to that which is "lawful and non-commercial." More restrictive licenses grant these rights only for a limited period of time.

Some would argue that source licenses that restrict the use or the creation of derivative works are not really open source. This, however, is the most common form of licensing use in academia, which is driving the so-called open source movement and is a main provider of useful source code.

Surprisingly, licenses that completely prohibit executing the software can still be useful. The trend is a new one, but I've seen it applied to the source code in books about algorithms and coding techniques. These books provide source code, but they restrict its use to study purposes only. You cannot copy the software, be it directly, by optical recognition, or even by typing it in, which eliminates any possibility of passing it through a compiler, much less executing it.

If the license fits

If all you want to do with a given open source package is use it as a tool to produce work separate from the package, then most open source licenses will do. Tools like compilers and text editors fall into this category. Libraries and interpreters might not, so pay attention.

For other purposes, choose public domain software. Or, if you want to distribute your software commercially but do not want to distribute the source to the modifications you made, go with a license like the MIT or the BSD. The GPL and LPGL are good choices if you don't mind distributing your source code.

Licenses like the Java Community Source License are so complicated that I'd keep away from the code unless I could count on the services of a good lawyer.

In all other cases, read carefully and look for the following keywords and phrases: use, copy, distribute, modify, derivative works, sublicense, and charge. Those words and phrases describe the rights that can be claimed on copyrighted work, and they will be specifically mentioned in documents that grant or restrict them. When in doubt, (gulp!) consult a lawyer.

If you're planning on distributing your own work as open source, then I suggest you adopt one of the licenses mentioned at the Open Source Institute's web site. I hope that my analysis will make the choice easier. These licenses have already been reviewed by lawyers and, just as important, they are free to use. Licenses can also be copyrighted, you know, and not all licenses are open source.