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JAX 08: 5 rules for a better software architecture (Update)

by Thomas,
assono GmbH, Standort Kiel,

A picture named M2

Alexander von Zitzewitz
5 Regeln für eine bessere Architektur
(5 rules for a better software architecture)

Your most frightening enemy: the Dragon of Complexity

Erosion of Architecture - Dragon Fire
Architecture erosion is quite a known problem

Typical symptoms of an eroded architecture
are a high degree of coupling and a lot of cyclic dependencies

Resistance to Change vs. time:
exponential ascent
do architecture management: higher cost in the beginning, big rewards over time

Architecture Management - Fighting the Dragon

Goal 1: Keep a simple and maintainable software structure

Goal 2: Keep complexity under control

Benefits: Dramatic reduction of overall
project cost

A Proven Architecture Meta Model

1. Step: Cut horizontally into Layers

User interfaces

Business logic

Data Access

2. Step: Cut vertically into vertical
slices by functional aspects





3. Step: Defines the rules of engagement

Matrix layer x slices: which block =
subsystems depend on which others?

Mapping of Your Code to the Meta

Each package is mapped to exactly one

If packages contain types of several
subsystems, virtual refactorings are helpful

A good naming convention for packages
can make your life very simple

should have interfaces

Work incrementally

How to measure coupling

ACD = Average Component Dependency

Average number of direct and indirect

rACD = ACD / number of elements (-->
it's always between 0 and 1)

NCCD is even more useful (normalized
components coupling dependency; comparison to balanced binary tree)

use Dependency Inversion to reduce coupling

the bigger the system, the smaller the
rACD should be

e. g. 500 elements, rACD < 7% might
be good

NCCD < 6 might be good (independent
from system's size!)

How to keep the coupling low?

Dependency Inversion Principle (Robert
C. Martin)

Golden Rules for a successful project

Rule 1: Define
a cycle free logical architecture down to the level of subsystems and a
strict and consistent package naming convention

Rule 2: Do
not allow cyclic dependencies between different packages

Rule 3:
Keep the coupling low (NCCD < 6)

Rule 4: Limit
the size of Java files (700 LOC is a reasonable value)

Rule 5: Limit
the cyclomatic complexity of methods (e. g. 15)

Rule 6: Limit
the size of a package (e. g. < 50 types)


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