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Generalizing Apdex

Today the Apdex specification is entirely focused on application response time. Its first paragraph defines Apdex as “a method for calculating and reporting a metric of transactional application response time in the form of an index with a value of 0 to 1.” But in reality, the Apdex method is much more widely applicable, and a more appropriate description is already spelled out in the first paragraph of the Wikipedia article on Apdex:

(Apdex) defines a standard method for reporting and comparing the performance of software applications in computing. Its purpose is to convert measurements into insights about user satisfaction, by specifying a uniform way to analyze and report on the degree to which measured performance meets user expectations. — Referenced on May 7, 2010

Of course, there’s a good reason why Wikipedia reflects the broader view. Over the years, the idea of generalizing the Apdex standard to apply in other domains has been discussed periodically within the Apdex community. So when I created the Apdex wiki description in 2007, I already had those discussions in mind.

After the current Apdex spec was ratified in 2007, some work began on drafting a more general version. But it was just a background activity for the participants, myself included, and no progress has been made over the last 18 months. I think it’s time to revive those discussions, so I’m going write a series of posts on the subject here. I’m not sure how many posts it will take, because some of this will be a brainstorming exercise, and I’ll be giving free rein to my imagination, while at the same time aiming to keep the posts reasonably concise.

Plan of Attack

Here’s my rough outline for exploring this subject matter. My notes tell me that each of these topics will probably require more than one post:

  1. Core Apdex qualities and/or features that apply across measurement and reporting domains
  2. Features that can (and should) be generalized, and why
  3. Ideas for implementing configuration options
  4. Ensuring compatibility with existing standards, methods, and metrics
  5. Targets, zones, scores, and thresholds

The last topic is really the logical conclusion of  (3) and (4), but I’ve already spent enough time thinking about this topic to know that it deserves its own section.

Please Contribute

I intend to keep pushing this discussion forward, even if Peter Sevcik and I are the only ones participating. But if you’ve ever used Apdex, or thought about how it could be used, please do consider contributing your own thoughts in the comments. I will definitely reply, and also do my best to take any public input into account. The resulting conclusions will be much more authoritative, and closer to becoming a usable and useful standard, if they reflect the consensus view of the people who want to apply Apdex.

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