Software Modifiability Tactics Quiz

Lecture Two: Architectural System Requirements

• System requirements are categorized into three: functional requirements (FR), non-functional requirements (NFR), and constraints.
• Functional requirements (FR) define what the system should do.
• Non-functional requirements (NFR) include quality attribute (QA) requirements and operational requirements.
• Constraints are the limitations or boundaries within which the system must operate.
• Quality attributes (QA) are orthogonal to functionality.
• Functionality and quality attributes, while not unrelated, can be tightly linked in practical application.
• Example FR: submitting an order
• Example NFR: Availability (7-5 Mon-Fri)
• Non-functional attributes depend on functional attributes in regards to use and context

Quality Attribute Scenarios (QAS)

• QAS are used to specify quality attribute requirements.
• QAS structure allows examining the impact of quality attributes.
• It consists of six parts:
  • Source of stimulus (e.g. human, computer system)
  • Stimulus (action, condition or event)
  • Environment (system conditions)
  • Artifact (system components, collection of systems)
  • Response (actions taken by the system)
  • Response measure (measure used for testing the response)
• QAS can be general or specific to a particular system.

Availability

• Availability is concerned with system failure and its consequences.
• Key areas of concern include how failures are detected, what happens during a failure, acceptable duration of downtime, how failures can be prevented, the required notifications for failures, and how long it takes to repair the system.
• Availability is defined as the probability of operational status when needed.
• Example: Mean time to failure (MTTF) / (MTTF + Mean Time to Repair) (MTTR)

Performance

• Performance is about timing in relation to events.
• Key aspects include the speed of response after an event, from user requests or other systems.
• Performance response is complicated by numerous event sources.
• Arrival patterns can be periodic, stochastic, or sporadic.
• Key performance measures include latency, deadline, throughput, jitter, and miss rate.

Quality Attributes: Other Considerations

• Standard ISO/IEC 25010 encompasses various quality attributes including adaptability, installability, replaceability, confidentiality, integrity, non-repudiation, security, accountability, authenticity, modularity, reusability, analysability, modifiability, and testability. Factors such as performance efficiency, capacity, resource utilization, and time behavior are also important.
• Different quality attributes can generate overlapping concerns.

Architectural Tactics

• Architectural tactics are design decisions that affect how quality attribute requirements are met.
• Some tactics ensure the achievement of the system's goal, others help manage the QAS by influencing responses.
• Availability tactics focus on fault detection, prevention, and recovery.

Availability Tactics (Categories)

• Fault Detection
• Fault Prevention
• Fault Recovery

Fault Detection Tactics

• Ping/echo, monitor, heartbeat, condition monitoring, and voting (using replication, functional redundancy, analytic redundancy)
• Each detect fault in a system in different ways

Fault Recovery Tactics

• Active redundancy (hot restart)
• Passive redundancy (warm spare)
• Spare (cold spare)
• Exception handling (correcting exceptions, retrying operations)
• Rollback (restoring the system to a known good state)
• Software upgrade (in-service execution, upgrade without affecting service).

Fault Prevention Tactics

• Removal from service
• Transactions (bundling updates to make them atomic, consistent, isolated, and durable)
• Predictive models (monitor system health, take corrective actions, predict future faults)

Interoperability Tactics

• Systems must successfully exchange information (locate tactics) and (manage interfaces tactics).
• Aspects: providing services with correct sequence, modifying information to be accepted by the other system.
• Tactics include discover service, orchestrate, and tailor interfaces.

Modifiability Tactics

• Tactics control time and cost of changes (implementation, testing, and deployment), including: localizing modifications, preventing ripple effects, and deferring binding time.
• Tactics include split module, increase semantic coherence, encapsulate

Security Tactics

• Tactics are divided into those for resisting attacks, detecting attacks, and recovering from attacks.
• Analogy tactics are useful to explain the methods of dealing with attacks.
• Techniques used for detecting attacks are intrusion detection, service denial detection, and message integrity verification and message delay detection.
• Tactics for preventing attacks include identifying actors, authenticating actors, authorizing actors, limiting access and locking computers. Methods are needed for controlling the system in these three different dimensions.

Architectural Patterns

• Architectural patterns are reusable resolutions to common design problems in software architecture.
• Patterns address context, preconditions, problem, and the solution as well as its properties and a set of elements.
• Several types of patterns (or styles) exist, including layered, broker, model-view-controller, pipe-and-filter, client-server, peer-to-peer, service-oriented architecture (SOA), shared-data, and map-reduce, and multi-tiered architectures.

Architectural Styles (Examples)

• Layer
• Broker
• Model-View-Controller
• Pipe-and-filter
• Client-Server
• Peer-to-Peer
• Service-Oriented Architecture (SOA)
• Shared-Data
• Map-Reduce
• Multi-Tier

Test your knowledge on modifiability tactics in software engineering. This quiz covers concepts such as rollback, in-service upgrades, and the impact of module coupling on system modifications. Dive deep into the strategies that enhance software adaptability and maintainability.