Open Source Software (OSS) is a category of software whose source code is made available to the public, allowing anyone to view, use, modify, and distribute the software. OSS is governed by a set of principles and licenses that define its characteristics and usage terms. Let’s explore the principles of open source software and some key open source licenses:
Principles of Open Source Software:
- Free Redistribution: Open source software can be freely redistributed, meaning anyone can share it with others without restrictions.
- Source Code Access: The source code of the software must be made available to users. This transparency allows users to understand how the software works and make modifications.
- Derived Works: Users have the right to create derived works, which are modified versions of the original software. These derived works must also be open source and subject to the same licensing terms.
- No Discrimination: Open source licenses should not discriminate against any person or group. They must apply equally to all users, regardless of their purpose (e.g., commercial or non-commercial use) or their identity.
- No Restriction on Fields of Endeavor: Users can apply open source software in any field of endeavor without limitations. Open source technology is versatile and adaptable to various applications.
- Distribution of License: The licensing terms of open source software must apply to the entire distribution. This ensures that derived works remain open source as well.
- License Must Not Be Specific to a Product: Open source licenses should not be tied to a specific product or technology. They should be applicable to any software that meets the criteria.
- License Must Not Contaminate Other Software: The use of open source software should not impose restrictions on other software used alongside it. In other words, it should not “contaminate” or force proprietary licensing on other components.
Key Open Source Licenses:
- GNU General Public License (GPL): The GPL is one of the most well-known open source licenses. It requires that any derived work based on GPL-licensed software must also be licensed under the GPL. It aims to ensure that the source code remains open and freely available.
- Apache License: The Apache License is commonly used for open source projects, especially in the context of web and server software. It allows more flexibility in combining open source and proprietary code while requiring proper attribution.
- MIT License: The MIT License is known for its simplicity and permissiveness. It allows users to do almost anything with the software, as long as they include the original copyright notice. It is widely used in both academic and commercial projects.
- BSD Licenses (e.g., 2-Clause BSD, 3-Clause BSD): BSD licenses are similar to the MIT License in their permissiveness. They allow for significant freedom in using, modifying, and distributing the software. The main difference is the inclusion of an advertising clause in the 3-Clause BSD License.
- Mozilla Public License (MPL): The MPL is designed to balance open source principles with the ability to create proprietary derivatives. It allows combining MPL-licensed code with proprietary code, as long as changes to MPL-licensed portions are made available under the MPL.
These licenses, along with others, provide a legal framework that ensures the open source nature of the software while offering varying degrees of freedom and flexibility to developers and users. The choice of license often depends on the goals and philosophy of the open source project.