Making Software

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

Metric	FreeBSD	Linux	Solaris	WRK
Version	HEAD 2006-09-18	2.6.18.8-0.5	2007-08-28	1.2
Configuration	i386 AMD64 SPARC64	AMD64	Sun4v Sun4u SPARC	i386 AMD64
Lines (thousands)	2,599	4,150	3,000	829
Comments (thousands)	232	377	299	190
Statements (thousands)	948	1,772	1,042	192 ...