Wednesday, December 21, 2011

SPRUCE - A Way of Thinking About Software

Analyzing and comparing software can be a complex task and I needed a way to break it up into components to avoid being overwhelmed by the details. These six top-level categories help keep me organized: Security, Performance, Reliability, Usability, Community and Economy. I call it Spruce to make it easy to remember. It works equally well when thinking about operating systems, languages, frameworks and individual applications.

A brief summary of Spruce:

Security - Protection of sensitive data through passwords and encryption is the visible part. The invisible part that is hard to measure is how much exploitable surface area is exposed to an attacker. That may not be initially obvious and it generally takes experience to develop a sense for the size of the risk. There is overlap with reliability with regards to attack-resistance.

Performance - We're concerned with the resources it requires relative to its alternatives. How well does it scale as the problem size increases and what trade-offs are unavoidable to achieve scale (ex: consistency vs. availability)? There can be overlap here with economy if it requires expensive hardware to achieve reasonable performance.

Reliability - This is about attack-resistance, fault-tolerance, error-correction and recovery. How gracefully does it deal with hardware/power failures, incorrect input and outright data corruption? There is overlap with security with regards to dealing with attacks. Can it keep running even under adverse conditions or does it go down every time the wind shifts direction? Has it been battle-tested or are you the brave pioneer? If redundancy is required there is overlap with economy.

Usability - This is considered from the point-of-view of the user or programmer as appropriate. I'm concerned with documentation, user-experience and API design. How well does it adapt to problems the original developer did not anticipate? Is it a pleasure to use or does it make you regret your career path?

Community - This is anyone who can provide you with help and enhance the usefulness of the product. It ranges from support from the original developer to a vibrant third-party community pushing the tech forward. Is it easy to get answers to questions and solve problems? How often is it mentioned on Stack Overflow and GitHub? Can you find developers who are eager to work with it or do they consistently forget to return your calls when you tell them the name of the underlying tech?

Economy - We're interested in the total cost of ownership relative to its alternatives. The visible parts are licensing fees, support contracts and hardware requirements. The invisible parts are the impact it has on other decisions. If it turns out you made the wrong decision how expensive is it to correct the mistake?

Engineering is all about trade-offs so it's rare that any tool excels in all of these areas. Reliability may be emphasized over performance or economy. Community might trump everything else. The key thing is to simply be aware of what the trade-offs are and be conscientious about them.

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