Recent moves by such companies as Sun Microsystems and Computer Associates to dip their toes into the world of open source have reawakened interest in how open-source software licenses work, and what benefits they bring to software companies—if any.
When companies such as Sun talk about making important products open source, what theyre really interested in, say industry observers, is the open-source business model—the model that has allowed Red Hat, Novell and others to draw on the efforts of thousands of Linux developers around the world. Linuxs GNU GPL (General Public License) has some requirements that wouldnt be acceptable to many businesses, so over the years alternative versions have been created that allow companies more flexibility. Some of these, such as the MPL (Mozilla Public License), have become popular templates for companies wishing to draw on open-source developer resources while retaining the ability to sell their products in a conventional commercial environment.
Two factors limit the options of commercial software makers when they decide to switch to an open-source license, analysts say. One is whether they want the open-sourced code to integrate with software using other types of licenses, something thats difficult or impossible under the GPL. The other is that companies often dont own all of the code in their products, so that the GPL is often out of the question. This is the case with Solaris, for example, which uses code licensed from The SCO Group.
So what exactly can be called "open source"? The Open Source Initiative, which invented the term in the first place, maintains a definition of what constitutes an "open" license, and lists those that fit the definition; the detailed list can be found on the groups Web site. The basic idea is to give developers a stake in the software, not just by allowing them to look at the code, as in Microsofts "shared source" scheme, but by letting them modify and redistribute it as well. Therefore, an open-source license must not, for example, restrict redistribution and must allow modifications and derived works.
Within this definition, however, there are a wide range of possibilities. The main difference between the major types of licenses is whether they allow derived works to be returned to proprietary form, and whether they allow integration with other types of licenses.