Prescriptive vs. Descriptive Architecture
Prescriptive Architecture
A system’s prescriptive architecture captures the design decisions made before system construction.
It represents the:
- As-conceived architecture
- As-intended architecture
Descriptive Architecture
A system’s descriptive architecture describes how the system has actually been built.
It represents the:
- As-implemented architecture
- As-realized architecture
Architecture During System Evolution
When a system evolves, ideally its prescriptive architecture is modified first.
In practice, the system and its descriptive architecture are often modified directly.
This can happen because of:
- Developer sloppiness
- Short deadlines that prevent proper thinking and documentation
- Lack of documented prescriptive architecture
- Need or desire for code optimization
- Inadequate techniques or tool support
Architectural Degradation
Architectural degradation includes two related concepts:
- Architectural drift
- Architectural erosion
Architectural Drift
Architectural drift occurs when principal design decisions are introduced into the descriptive architecture that:
- Are not included in, encompassed by, or implied by the prescriptive architecture.
- Do not violate the prescriptive architecture’s existing design decisions.
Architectural Erosion
Architectural erosion occurs when architectural design decisions are introduced into the descriptive architecture that violate the prescriptive architecture.
Architectural Recovery
If architectural degradation is allowed to occur, the system’s architecture may need to be recovered.
Architectural recovery is the process of determining a software system’s architecture from its implementation-level artifacts.
Examples of implementation-level artifacts include:
- Source code
- Executable files
- Java
.classfiles
Implementation-level views can become complex and virtually incomprehensible, making architectural recovery important.
