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Making Software by Greg Wilson, Andy Oram

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Into the Battle

No battle plan survives contact with the enemy.

Helmuth von Moltke the Elder

The key properties of the systems I examine appear in Table 15-1. The quality metrics I collected can be roughly categorized into the areas of file organization, code structure, code style, preprocessing, and data organization. When it is easy to represent a metric with a single number, I list its values for each of the four systems in a table, and on the left I indicate whether ideally that number should be high (↑), low (↓), or near a particular value (e.g., ≅ 1). In other cases we must look at the distribution of the various values, and for this I use so-called candlestick figures, as in Figure 15-3. Each element in such a figure depicts five values:

  • The minimum, at the bottom of the line

  • The lower (25%) quartile, at the bottom of the box

  • The median (the numeric value separating the higher half of the values from the lower half), as a horizontal line within the box

  • The upper (75%) quartile, at the top of the box

  • The maximum value, at the top of the line

  • The arithmetic mean, as a diamond

Minima and maxima lying outside the graph’s range are indicated with a dashed line, along with a figure of their actual value.

Table 15-1. Key metrics of the four systems

MetricFreeBSDLinuxSolarisWRK
VersionHEAD 2006-09-182.6.18.8-0.52007-08-281.2
Configurationi386 AMD64 SPARC64AMD64Sun4v Sun4u SPARCi386 AMD64
Lines (thousands)2,5994,1503,000829
Comments (thousands)232377299190
Statements (thousands)9481,7721,042192 ...

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