Arcitecture - Decision

Architectural Decision

• Architectural decisions are design decisions that address architecturally significant requirements; they are perceived as hard to make and/or costly to change.
• Architecturally significant requirements(ARSs) are those requirements that have a measureable effect on a software system's architecture.
• It is necessary to manage the relationship between quality requirements and structural decision making.
• There is a trade-off relationship in quality that is important depending on one variable.

 

Architecture Drivers

• Architectural drivers are requirements that will shape the software architecture.
• Architectural drivers include : 

 

Functional Requirements

• What a system must compute
  Describes the core functionality of the system from a user's perspective
  Avoids details of implementation
• Usually available as part of a standard requirements specification for a product.
  However, some functional requirements may be hidden
  Examples : error behavior.

 

Constraints

• Describes the context
  - Decisions that are already made about the design
  - Factors that influence the design

 

Quality Attributes

• Function and quality could be confused.
  
• If it is originally required, it is a function.
• Define qualities that a system must have beyond its functionality
• Functionality and qaulity attributes are largely orthogonal.
• Architectural choices implement functionality, promote some quality attributes, and inhibit others. Tradeoffs.

 

Performance

• Source : Internal or external to the system
• Stimulus : Arrival of a periodic, sporadic, or stochastic event
• Artifact : System or one or more components in the system
• Environment : Operational mode : normal, emergency, peak load, overload
  
• Response : Porcess events, change level of service
• Response Measure : Latency, deadline, throughput, miss rate

 

Performance Tactics

• Control Resources Demand
• Manage Resources

 

Modifiability

• Reduce size of a module
• Increase cohesion
• Reduce coupling
• Defer binding

 

Availability

• How to respond to unusual situations is important.
• When a crash occurs, how is it restored?

 

 

Quality Characteristics