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Generalizing the Apdex Language

I’m writing a series of posts about Generalizing Apdex. This is #7. To minimize confusion, section numbers in the current spec are accompanied by the section symbol, like this: §1. The corresponding section numbers in the generalized spec, Apdex-G, are enclosed in square brackets, like this: [1].

In my previous post, I reviewed the Apdex specification systematically, asking Which Apdex Features Can Be Generalized? That exercise showed that creating a general version of the spec involves more than generalizing the rules for implementing the features of Apdex; the language describing those features must be generalized too.

The current spec is grounded in a conceptual model of a specific measurement domain. Its language refers to users of an application being productive based on the responsiveness of a human-computer interface. We encounter this as soon as we begin reading Section §1, shown in the left-hand column below. In the new generalized specification documents, that terminology belongs in the domain-specific addendum, Apdex-R, which will deal with how to apply the Apdex method to response time measurements.

In Apdex-G we need abstract language describing only the properties of a metric. If more concrete language is needed to clarify an explanation, if must appear in an illustrative example. The only exception is text in Apdex-G describing the origins of Apdex.

To illustrate how we might apply these guidelines, the right-hand column below suggests possible replacement text. Consider this text to be a first draft the opening paragraph(s) of Apdex-G Section [1], corresponding to the current preamble of Section §1.

§1. Introduction

The Apdex Alliance is a group of companies collaborating to promote an application performance metric called Application Performance Index (Apdex). Apdex is a numerical measure of user satisfaction with the performance of enterprise applications, intended to reflect the effectiveness of IT investments in contributing to business objectives. The Apdex metric may be used by any organization seeking insight into their IT investments. This specification defines Apdex, which is 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.

[1] Introduction

Apdex (Application Performance Index) is a metric that reflects the degree to which a set of performance measurements achieves designated targets.

Originally designed as an index of user satisfaction with the responsiveness of enterprise applications, Apdex can also be used to report on many other quality measures, such as the degree to which a product conforms to technical standards, or the degree to which a service achieves business objectives.


  1. To begin the spec with a definition of the Apdex Alliance seems to be putting the cart before the horse. It would be more appropriate to defer any reference to the Alliance until Section [1.1] and focus only on the Apdex metric here.
  2. This preamble to Section [1] seems to be the logical place to include a brief reference to the history of Apdex, as a way to bridge from the Apdex name and the original intent of the standard to other, more general, applications.
  3. The fact that the index produces a value between 0 and 1 seems to be an unnecessary amount of detail in an introduction. This fact will be listed, together with other essential characteristics, in Section [2.1].

Measurement Terminology

I have been particularly careful how I use the terms “measurement,” “measure,” “metric,” “indicate/indicator,” and “index.” The Apdex-G spec contains abstract descriptions and definitions that must be read and understood separate from concrete illustrative examples. This heightens the need for precision in its fundamental terminology, to avoid potential confusion. Rather than writing more about that topic here, I will add my definitions to the Glossary.

If further terminology issues arise and need to be documented, I will extend this post.

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