Software Quality Management (SQM)

A practice to quantitatively plan and guide software development, emphasizing Quality engineering, plan & control

• Ensures req'd level of quality is achieved in software product
• Defines appropriate Quality framework, standards, and procedures
• Quality framework, standards, and procedures are followed
• Develop a quality culture - it's everyone's responsibility

Achieving Quality Factors

• Architectural based Tactics:
  • Quality models
  • Development models
  • Common sense
• Architectural based Analysis and trade-off approach:
  • General properties essential for quality factors
  • Scenario based, quality factors required will satisfy goals

Reliability

Prevent/tolerate faults! Recover or handle fault to recover/limit damage.

Active fault detection

• Periodically check for symptoms OR anticipate when failures will occur

Tolerating by exception

• Situations that cause the system to deviate from its desired behavior
• Apply exception handling with ability to bring system to acceptable state
• Typical exceptions include:
  • Deadlocking
  • Violating a system invariant (e.g.; security property)
  • Corrupting data
  • Failing to provide a service
  • Providing the wrong service

Fault recovery tactics

• Undoing transactions: manage a series of actions as a single transaction that are easily undone if a fault occurs midway through the transaction
• Checkpoint/rollback: software records a checkpoint of current state; rolls back to that point if system gets in trouble
• Degraded service: return to previous state with the least possible degraded service

Security

Architectural Characteristics:

Immunity

Ability to prevent attacks

• Minimize exploitable security weaknesses
• Ensure security feats are included in the design

Resilience

Ability to recover quickly and easily from an attack

• Segmenting functionality to contain attack
• Enable system to quickly restore functionality

Efficiency - constraints on system speed & accuracy

Response Time

Speed of response to requests

Throughput

Requests/minute

Load

How many users it can support before response time/throughput suffer

Improve Efficiency:

By Perceived Response Time:

Scheduling

• Earliest deadline first
• First come/fist served (FIFO)
• Explicit Priority

Caching

By Utilization of Resources:

Load-Balancing

As a reverse proxy, distributes network or application traffic across a number of servers to increase users and app reliability

Maintainability

Design must be able to change

Directly affected Units

responsibilities change to accommodate a system modification. Minimize impact and focus on

• Expected changes: design decisions most likely change. Put each in it's own software unit

• Cohesion: increases chances that a change to system's responsibilities are confined to the few units that are assigned those responsibilities

  Indirectly affected units

  implementations must be revised, responsibilities remain the same. Focus on reducing Dependencies:

  • Coupling: reduces likelihood that change in one unit will affect others
• Interfaces: If a unit interacts with other units only through their interfaces, changes to one unit won't go beyond the unit’s boundary - unless its interface changes

Self-Managing Software

autonomic, adaptive, dynamic, self-configuring, self- optimizing, self-healing, context-aware

Systems that operate optimally in different/changing environments - monitors environment and it's own performance, and changes in response

Usability

Quality of a user's experience when interacting with a product/system. The user's effort for:

• Understandability: recognizing logical concept and applicability
• Learnability: learning it's application (i.e. operation control, input, output)
• Operability: operation and control.