Agile Design

Problems with software designs

RigidityFragilityImmobilityViscosityNeedless ComplexityNeedless RepetitionOpacity

RigidityRigid software is difficult change

One change requires mods in multiple modulesChanges are more difficult than estimated

FragilityThe degree to which it is easy to break the

programSmall changes generate unexpected side-

effects

ImmobilityThe code is not modular enough for reuse

ViscositySoftware Viscosity

When design-preserving methods of extending the software are less easily achieved than changes that are not in concert with the overall design (i.e., hacks are easier than following design) the design has “high viscosity.”

Environment ViscosityThe process of making changes (e.g., compiling,

getting approval, configuration management) can also encourage a “quick-and-dirty” fix, rather than a fix better suited to the long-term maintainability of the system.

Needless ComplexityPreparing for unknown extensions

Overly flexibleBad AlgorithmsBad/Out-dated assumptions about system

priorities

Needless RepetitionCut and paste is evil in software engineering.

How many places does the same processing occur? That is the number of places that changes/fixes

must be madeDo people understand what the cut and paste?

This is how software the literally no one understands enters the system.

The same code, with minor changes, makes the minor changes easy to miss.

OpacityHow clear is the code

Code tends to get less clear as it is modifiedCode tends to get less clear when you think

about something else for a whileCode that is clear to you, might not be clear to

others