Shared source

From Academic Kids

Shared Source is an open source-like form of code sharing which is generally more restrictive than true open source, but less so than proprietary code. The term is most often used to mean one of Microsoft's Shared Source Initiatives, but similar licenses have also be used by other companies such as Hewlett-Packard, and a number of Microsoft .NET related projects such as OpenNETCF (

With shared source, the source code to a particular piece of software is made available for reference. However, unlike most open source licenses, the authors maintain strict control over the use of that code once it has been read. For example, many shared source licenses permit only academic use of the source code, or permit reuse of the code only for non-commercial use, or permit reading but no deriving from the code base.

Proponents of shared source see it as a step forward from purely proprietary development. In the particular case of Microsoft, their shared source initiatives often permit developers to see source code they otherwise would have no access to. This permits better integration, debugging, interaction, and standardization among products.

Opponents of shared source often see shared source licenses as no better (in terms of software "freedom"), or in some cases even worse, than proprietary licenses. Many outspoken open source advocates consider the shared source licenses as illusory. That is, they give the impression that they are making the source code freely available, when in fact there are critical restrictions on the code's use. There is also growing concern that the shared source program is being used to harvest the names of developers for future legal action if they ever participate in development project seen as competitive to a Microsoft product.


Benefits of Shared Source

Shared source licenses provide a number of benefits to end users that are not present in typical proprietary software licenses. Primary among these is the availability of source code for reference when developing complimentary systems. For example, having the source code to significant portions of an operating system aids application developers in maintaining stability and consistancy in their own programs. The availability of source code also permits review and auditing from a security perspective, something which many large corporations and governments are now mandating.

Shared source benefits the copyright holder in that much tighter control is kept over the use of their product than open source licenses, which generally include the voluntary abdication of many of the author's rights. From the perspective of companies which are used to developing proprietary software, this is a smaller transition to make, and may be seen as an interim step to full open source disclosure.

From an end-user and original author perspective, shared source licenses share many of the benefits (and drawbacks) of open source licenses. However, from a "downstream" developer's standpoint, shared source licenses stop well short of the rights granted by an open source license. This difference is the source of much of the criticism levelled against shared source (see below).

The Shared Source CLI

The first widely-distributed shared source license is that covering Rotor, the shared source implementation of the Microsoft .NET CLI. This implementation is freely available, including source code, as a reference guide. The license explicitly permits non-commercial use of the source code, including derived works. It explicitly forbids use of the code, or derivatives, in any commercial software or, notably, open source software. (One of the provisions is that derived works must use a license that is at least as restrictive as the original shared source license.)

Shared Source Windows(TM)

As part of the settlement with various national and state governments, Microsoft has begun releasing portions of their existing code base under shared source licenses. For example, under a number of such licenses, developers can gain access to portions of Microsoft Windows itself. These are among the most restrictive of the shared source licenses, and are generally available only to large companies which Microsoft considers enterprise-level partners.

Shared source critics

Open source advocates have spoken out quite often on the problems or limitations with shared source licenses. Among the most commonly levelled criticisms are:

  • The term shared source is primarily a marketing technique, deliberately meant to create confusion with open source among developers or management who have no prior experience. More specifically, the intent is to convince "the public" to use a shared source license as opposed to an open source lisence, or to give a company the appearance of more cooperative interaction with their user base than truly exists.
  • Modification of the code is not permitted, including sending code modifications back to the author. You are not allowed to modify code or write patches against the code, even for internal use. For this shared source is dubbed "source code under glass".
  • You may not incorporate shared code into any other program. Some people even fear that shared source code may "taint" a developer with knowledge of the licensed code, thus preventing participation in open source projects where such code may be inadvertantly included in violation of the shared source license.
  • Shared source is mainly an attempt to appease customers who want the ability to evaluate the code and audit its safety, not to modify it according to their needs. While definitely a benefit to those customers, it capitalizes on the similarity between the terms shared source and open source in an unrealistic way.
  • You do not get a complete, working copy of a real program's source. Instead, you are given access to specific portions of a program, or to a "reference work". Consequently, it's difficult to say whether or not the source code you have accurately reflects a real program.

It is important to note that Shared Source, much like Open Source, is not a single license (see the links below). Rather, it is a collection of similar licenses, each with their own legal terms, benefits and drawbacks. For example, many of the Windows CE Shared Source programs explicitly permit deriviate works. The problems with shared source described above are, however, common to the large majority of such licenses, and the generally understood purpose of the shared source concept as a whole.

External Links

High Profile Shared-Source Criticisms:

Note that the Shared source licence is NOT considered a Free software licence, putting it in this category is just a way to compare it to other open source licences, it's also the answer of Microsoft to the open source or Free software movement.

de:Shared Source pl:Shared Source


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