Mixed-source software development

In the past years, the amount of software in products has risen dramatically. Not only do devices today contain more and more software, but also a larger part of the functionality is realized in software. This explosive growth has driven up the cost of software development. Outsourcing (parts of) the software development provides a partial solution. Use of open source for the right parts can provide significant additional cost savings and reduction in product development times.

This requires a two-step strategy. First, classify features as differentiating, baseline or commodity features and determine for each whether using open or closed software is the best choice. Second, the software architecture should be designed with these legal design goals in mind. This requires close cooperation between the software architects and engineers and the IP and legal professionals.

Open source

Software packages such as the Linux operating system, the Firefox web browser or the Apache web server software are the most well-known examples of open source. More generally speaking, the term open source refers to a software development model by which the source code to a computer program is made available publicly under a license that gives users the right to modify and redistribute the program. Users are expected (although not required) to also make their modifications and improvements available for inclusion in the "official" distribution.

The use of open source software is not just restricted to software companies or consultancy firms such as IBM. Consumer electronics products and other devices also increasingly use open source. For example, Linux is the most popular choice as embedded operating system today. A good introduction to the business benefits open source software can bring is Martin Fink's book The Business and Economics of Linux and Open Source (Prentice Hall, 2002).

Understanding open source risks

The license conditions applicable to open source can be quite peculiar. For example, some licenses require one to release one's own software as open source software itself, if that software incorporates the open source software. If open source software under such a license is used throughout the software stack in a product, all software for that product may have to be published as open source. (These requirements only apply when such software is sold or transferred to third parties.) For patent holders the additional risk exists that one may have to give a free patent license when distributing third party open source software that infringes on one's patent. This patent license could be limited to only the open source in question, but in some cases even to the software stack as a whole.

Because of these risks, a company may be tempted to avoid open source software altogether. This however is not a realistic option from a business point of view. The use of open source software is gaining more and more popularity in commercial environments and even in commercial products. By ignoring this, a company locks itself out from all the available high-quality software and does not benefit from the reduced costs and time to market that open source software implies. In some cases it is simply not feasible for a commercial product to keep up feature-wise with open source alternatives. The only viable option therefore is to understand the risks and how to manage them.

Open source licenses

There are over 40 different open source licenses, each with their own conditions and implications. Roughly they can be classified into these three categories:

  1. Free-for-all licenses: these licenses only require licensees to give credit to the original authors. Derivative works can be kept proprietary. Sometimes these licenses are referred to as "academic licenses". Examples are the so-called BSD and MIT licenses as well as the license used for the Apache Web server.
  2. Keep-open licenses: modifications to software under these licenses have to be made available as open source as well. Larger works incorporating such software can be kept proprietary. The GNU Lesser GPL (used for Linux system libraries) and the Mozilla Public License (used for the Firefox Web browser) are Keep-open licenses.
  3. Share-alike licenses: when software under such a license is modified or extended, the result as a whole has to be made available as open source. The term copyleft is sometimes used to characterize this kind of license. The most famous example is the GNU GPL, which applies e.g. to the Linux operating system. Another example is the Open Software License (OSL).

A company may be tempted to avoid having to share software it considers proprietary by disallowing use of Share-alike and even Keep-open licensed open source. This will severely limit the ability to use open source at all. About 65% of all open source software is covered by the GNU GPL, with an additional 20% being covered by the GNU Lesser GPL. These two licenses thus cover virtually all key components of devices with embedded software. Hence an open source policy should be about where and how, not if, the different types of open source can be used in a product.

Open or closed?

Companies that use open source often make a purely black or white decision: either a product is open source or it is not. Much greater benefits can be obtained by using a more subtle approach. A company can use open source for certain features and use closed, in-house developed or commercially licensed software for other features if the above-mentioned license implications are properly managed. The ultimate goal should be to ensure the product offers the most value. Therefore, a proprietary feature or solution should be replaced with an open source alternative when doing so represents a larger value than keeping the feature proprietary or closed. Instead of using an existing open source implementation, a company could of course also release its own implementation as open source.

Value of product features

Value can be obtained through different strategies. When a feature is kept closed or proprietary, the feature can serve to differentiate the product over competing products. Alternatively, the feature can be licensed to others for a royalty fee, for example as a software library or a chip with embedded software. Patents related to the feature can be licensed royalty-bearing as well. A consequence of this approach is that the feature now must be written in-house or be licensed-in from a third party, which increases product cost.

Using open source software for a feature does not carry software license costs, although in some cases, for example when the feature implements a royalty-bearing standard, a patent royalty may still be due. The software can be adapted if necessary and there is no dependence on a particular vendor. But licensing the software, or any relevant patents, for a royalty is no longer possible.

Commoditize your complement

To find the right strategy, keep in mind an old rule in economics: make the complement of your own product a commodity. A complement is needed to make your own product useful. Digital music complements portable music players, for example. Commoditizing your complement actually stimulates demand for your own product. If digital music becomes easier to purchase online, demand for music players goes up.

This not only applies to complete products, but also to components or features of a single product. An advanced digital television may have the ability to automatically generate one-minute summaries of available television programs. The ability to decode and play digital video streams is essential to make this feature useful, and so video decoding is a complement to automatic summary generation.

Often commoditization goes hand-in-hand with standardization. Once a feature is standardized, anyone can build an implementation by following the standard. Soon afterwards the feature becomes a commodity, as there now are many more-or-less interchangeable implementations available. In the examples above, it is in the interest of the television and music player manufacturers to ensure digital content formats are standardized.

Open source to complement differentiators

In principle open source is appropriate for those features that complement the differentiating features of a product. But using open source for all non-differentiating components can be a step too far. Some non-differentiating features provide more value when closed than when open, and so should remain closed. For instance, if a feature is being licensed for money to others, then open sourcing that feature cuts off a stream of revenue. If the component is closely linked with a differentiating feature, and the only available open source implementations are licensed under Share-alike licenses, the differentiators might also have to be made available as open source.

Product feature categories

There are three categories of features that need to be considered:

  1. Differentiators: these features provide added value to product. They give an 'edge' over the competition and provide a reason why customers want to buy the product.
  2. Baseline: these features are necessary and expected by customers. They provide value, but no added value to the product. For example, today no one buys a portable music player because it supports the MP3 format. On the other hand, no one would buy such a player if it does not support MP3.
  3. Commodities: these are hidden, uninteresting features. They are needed to make the product work but the customer doesn't care about them.

Figure 1: The make/buy/open source decision

Figure 1: The make/buy/open source decision

For each category, the classic question "make or buy" now becomes "make, buy or open source?" To answer this question for a particular feature, the first step is to classify it as either a differentiator, a baseline feature or a commodity feature. Second, for each feature the impact of each option (make, buy or open source) should be made. The diagram in figure 1 shows the impact of each.

Handling differentiators

Generally speaking, differentiators should be developed in-house to ensure maximum market advantage. Outsourcing (buying) such features is an option, but that means a company relies on a third party for the most critical parts of its product. This creates a significant risk should the third party run into problems. And of course open sourcing such a feature is usually not a good idea, as doing so would turn the feature into a commodity.

Handling commodity features

The opposite holds true for commodity features. A company should not spend time and effort in-house to develop or maintain such features. Using open source here saves time, effort and money and thus usually is the right choice. An example is using Linux as an embedded operating system.

Handling baseline features

In the middle are the baseline features. Here a case-by-case approach to decide whether to make, buy, or use open source is most appropriate. A company might choose a rule of thumb, such as "we use open source unless the feature is being licensed for money to others" to help make the decision. Technical considerations may block a decision to open source a particular baseline feature. For instance, if open sourcing the baseline feature would require also open sourcing a differentiating feature, it is clear that that baseline feature should remain closed.

Handling special cases

In some particular situations open source can be inappropriate. An often-heard issue is that the open source license conditions could be too cumbersome or costly for a particular product. There could also be technical reasons to use a closed source alternative. For example, in a small embedded device Linux might not be the best choice because of its relatively large system requirements. Another reason is when a customer demands that no open source is used.

Legal software design

While this may seem straightforward enough in theory, the practice can be difficult. Building a software-based product is not a matter of putting components together like LEGO® blocks. Source code can be copied and pasted, libraries can be linked or accessed through remote procedure calls. With object-oriented languages like Java and Web-accessible services the possibilities grow even larger. This may create complex interactions and dependencies between the software components. Assessing the legal implications of open source code in such a complex software stack can be a difficult task.

To ensure these implications can be properly managed, IP professionals should get involved in the product design at an early stage. When an IP assessment has to be carried out on a fully completed software stack, making changes based on IP or legal considerations can be very difficult or costly. IP and legal design goals should be formulated at the beginning of the project, so that these can be taken into account during the design and implementation of the software.

Into the ABISS

A concrete example of how to put the above into practice is the so-called Active Block IO Scheduling System scheduler - ABISS for short. This Philips contribution to the Linux operating system enables real-time reading and writing of streams of data from a hard disk. This is an important topic, especially for audio or video playback.

Introduction to the ABISS scheduler

With ABISS, Linux applications can request real-time delivery of video or audio streams from a hard disk at a certain playback speed. ABISS either delivers the stream at the requested speed, guaranteed, or it tells the application that the request is not possible. Such a scheduler significantly enhances the design of a hard disk recorder or video player.

A key element of ABISS is its scheduler. The scheduler balances requests to make sure the desired rate can be delivered. The choice for a particular scheduling algorithm, or even the policies and rules to be used with the scheduler, can have a significant impact on the system's performance. A policy covers items such as the maximum number of files that can be open at once. Philips has spent a significant amount of research developing and fine-tuning fast and efficient algorithms and associated policies.

Why open source ABISS

For Philips, the reason to make ABISS open source was to establish the technology as a de facto standard. Further development of ABISS would be done jointly with the Linux community. This has several advantages. To name one, if the Linux hard disk access subsystem would change, the community would change ABISS accordingly if it were part of Linux.

Legal issues

In a straightforward implementation, ABISS would be implemented by modifying the Linux operating system directly. However, as Linux is licensed under the GNU GPL, that would mean ABISS as a whole would have to be made available under the GPL as well. Because that would commoditize the valuable know-how related to the scheduling algorithms and the associated scheduling policy choices, this was not desirable.

In addition, such an implementation could make it difficult for third parties to use ABISS for their applications. To drive wide acceptance of ABISS, it was important that ABISS could be used with proprietary (closed source) third party applications.

Legal design goals

The above was translated into three IP-related design goals:

  1. Allow any application to use the ABISS functionality.
  2. Allow any party to use proprietary scheduling algorithms in ABISS, and to tune them using proprietary know-how.
  3. Ensure changes to ABISS itself become available as open source.

The engineers worked with the IP department to redesign the ABISS architecture based on these goals. This resulted in several material changes to the ABISS architecture. The end result is illustrated in figure 2.

Figure 2: The ABISS architecture

Figure 2: The ABISS architecture

Redesign based on legal design goals

ABISS was redesigned from one big block of code to a framework into which scheduling algorithms and policy settings could be included as separate components. The framework was realized as a set of modifications to the Linux kernel. The scheduler was implemented as a so-called Loadable Kernel Module. Such a module is a separate component that interacts with the framework using a standardized Linux interface.

An application that wants to read or write a file with a guaranteed bit rate uses a system library that provides access to the ABISS functions. For technical reasons, the functionality to manage the scheduling policy and the scheduling algorithm was separated into two components. A background process (called a 'daemon' in Linux terminology) communicates with the ABISS framework to execute the scheduling policy. Policy settings are provided through a small component (a plugin) that is loaded by the daemon.

By designing the architecture in such a way that the scheduler and the policy were implemented as separate components, the above design goal 2 could be satisfied. The software that interacts with these components was licensed under a Keep-open license, which satisfies design goal 3 and allows the combination with proprietary scheduler and policy modules. Similarly, the library for applications that need to use the ABISS functionality was made available under a Keep-open license, satisfying design goal 1. The changes to the Linux kernel could only be licensed under a Share-alike license, but because of the ABISS architecture this had no consequences for the other licenses.

Releasing full implementation

When ABISS was released, a scheduler with basic functionality and policy settings was included. This basic scheduler shows ABISS is viable, yet it does not contain differentiating know-how. Releasing only a partial implementation (ABISS without scheduler) would have created a very negative impression.


Today many companies regard the use of open source as an ad-hoc decision, made by individual programmers when trying to meet deadlines. Formal open source policies often treat requests to use open source as a rare exception: "not allowed, unless". Significant business advantages can be obtained by actively selecting open source for certain features and using closed, commercially licensed software for other parts.

Policies regarding open source should not be presented as a prohibition but as part of a strategy to make effective use of open source. A positive attitude from the IP and legal professionals with good knowledge of software development issues is very important to get such a strategy off the ground.

Following such a strategy, the first step is to classify features as differentiating, baseline or commodity features and to determine for each whether using open or closed software is the best choice. Second, the software architecture should be designed with these legal design goals in mind. As the ABISS example shows, this requires close cooperation between the software architects and engineers and the IP and legal professionals. When done carefully, this approach achieves the best of both worlds.

This article appeared in Intellectual Asset Magazine issue 19, August/September 2006.