Thursday, August 08, 2013

Backwards Compatibility III - Planning For The Future

Dreaming Big

I like to daydream about my software projects from time to time. In my dreams, my software would become a worldwide sensation. It would be run on millions of computers operated by millions of users using various platforms and each having unique needs. My software would interact with thousands of third-party applications. Of course, my software would be flawless. Nonetheless, I would be forced to pander to the inept masses whose software is not worthy to interface with my magnificent technical achievements.

Down to Earth

In reality, most software that is written today will not see such widespread adoption. There are many software developers earning a reasonable living writing in-house software applications for use by a handful of employees in their own office. Others may have a wider impact, but will not go beyond a few thousand users in their niche market. While backwards compatibility is important for all developers to understand, it is rarely the highest priority for these types of software projects.

One example of software targeting the kind of compatibility required on a global scale is web servers. Web servers must be able to interact with an incredibly wide variety of devices and applications. They should also run on as many varied systems as possible to avoid limiting themselves to a single market. A web server needs to provide your grandmother's garage-sale Pentium II running Internet Explorer on Windows 95 with pictures of her family. It needs to provide content to yuppies browsing social sites on their iPhones during Saturday brunch. It needs to allow 14-year old Linux fanboys to post to their favorite hacker forums.

Identify Yourself

Perhaps the most straightforward way to plan for future compatibility is to add an identification protocol to each interaction. This lets applications on side of the interface know who they're dealing with and to compensate for known issues in their counterpart.

This is really not so dissimilar from interactions with people. You know not to mention your recent SUV purchase to your tree-hugging hippie friend named Rainbow. You probably avoid talking about your contempt for Justin Bieber to your teen-aged niece. In the same way, you can build up a list of known compatibility problems over time and compensate for them by adjusting your own software to avoid the problem or fix it in another way.

Identifying a unique name for each piece of software is not as simple as it may first seem. There are several key pieces of information required to uniquely identify each application: name, version, platform, and configuration.

The name distinguishes similar products with obviously different implementations and opportunity for discrepancies in behavior. For example, consider web browsers provided by different companies such as IE, Firefox, Chrome, etc.

The version is generally a sequential numbering system that can help distinguish older (buggy and limited) versions from newer (corrected and fully-featured) versions.

The platform describes the operating system and architecture on which a cross-platform product is running. This distinguishes the same product built for 32-bit Windows XP, 64-bit Windows 7, or 64-bit Ubuntu Linux.

Finally, the configuration may contain additional information about modifications, plug-ins, and settings that enable special features or trigger certain buggy behavior. This information can be very wide ranging, complex, and difficult to fully capture.

Once each application has verified the identity of its neighbor, it is able to accommodate known compatibility issues and limitations by changing its own behavior. Unfortunately, not all players are always working towards a common goal. These version identification techniques can be turned on their heads and used to limit or disable certain applications.

Expect New Features

With most software, there is a great incentive to add new bells and whistles and little incentive to trim the fat. New features are used to attract new customers and provide new capabilities. Old features may be missed if removed, and are generally simpler to retain than to completely remove.

A widely-used standard designed with this in mind is XML. This, of course, stands for Xtreme Markup Language (or eXtensible Markup Language if you're a real stickler).

XML is designed as a tree of nested tags with attributes and text. Well-designed XML libraries provide the ability to parse XML text into a data structure and to query for desired components within the tree. The beauty of this design is that adding new tags should not interfere with old logic. Older applications are completely free to ignore tags they do not understand and simply proceed as if nothing is different.

By using XML or similar extensible formats for data interchange, applications will be better prepared to accommodate any of the inevitable new features the future has in store.

Be Prepared

As the Boy Scout motto says, "be prepared." If you are designing a software product with the dreams of being compatible with a diverse range of other products and amenable to new features, you must plan for the future. A little planning up front will save you a great deal of grief later. Expect that incompatibilities will crop up and need to be addressed. Expect that new features beyond the original design will be required. Use an interface that is designed to help deal with these problems even before they arise.

Keep in mind that designing for the future can be challenging and time consuming. If you are writing an internal application with no plans for data exchange and targeting a single platform, you're probably best to stick with the "You Aren't Gonna Need It" (YAGNI) approach. Make sure you understand which type of application you are creating before you dive in too quickly and shoot yourself in the foot.


Joshua Ganes

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