Software Engineering - Architectural Design

Software Engineering - Architectural Design

• The design process for identifying sub-systems, the framework for sub-system control and communication is architectural design
• The output of this design process describes the software architecture
• Architectural design is an early stage of system design
• It links specification and design processes, often done in parallel with specification activities
• Identifying major system components and their communications is part of architectural design
• Changes in architectural design are not incremental; the cost of changing later is high, even in agile projects

Topics Covered in Architectural Design

• Architectural design decisions
• Architectural views
• Architectural styles/patterns
• Application architecture

Architecture of a Packing Robot Control System

• A diagram depicts a packing robot system
• Components include vision system, object identification system, arm controller, gripper controller, packaging selection system, and conveyor controller.

Architectural Abstraction

• Architecture in the small focuses on individual program architecture
• It concerns how an individual program is decomposed into components
• Architecture in the large focuses on complex enterprise systems, including other systems, programs, and program components
• These systems are often distributed over multiple computers owned by different companies.

Advantages of Explicit Architecture

• Stakeholder communication: Architecture can be a focal point for discussions among stakeholders
• System analysis: Helps analyze if the system meets its non-functional requirements
• Large-scale reuse: Architecture can be reused in various systems, leading to product-line architectures

Architectural Representations

• Simple block diagrams showing entities and relationships are frequently used to document software architecture
• These diagrams lack semantics, don't show all relationships, and don't always depict all entity properties

Use of Architectural Models

• Facilitating discussion on system design
• High-level architectural views are helpful for communication and project planning
• They avoid clutter with details
• System stakeholders can understand the overall system without getting bogged down in the minutiae
• Useful for documenting designs

Architectural Design Decisions

• Design is a creative process, methods change with the type of system
• Some common decisions impact non-functional characteristics

Further Architectural Design Decisions

• Generic application architecture?
• Distribution strategy?
• Architectural design styles?
• Structural approach for the system?
• Decomposition into modules?
• Control strategy to employ?
• Architecture evaluation method?
• Documentation strategy?

Architecture Reuse

• Systems in the same domain often have similar architectures reflecting domain concepts
• Application product lines are usually based on a core architecture with variants to meet specific customer needs
• Architectural patterns capture the essence of an architecture that can be instantiated in different ways

Architecture and System Characteristics

• Performance: Localize critical operations, minimize comms; use large components
• Security: Layered architecture, inner layers for critical assets
• Safety: Safety-critical features in a small number of sub-systems
• Availability: Redundant components and fault tolerance
• Maintainability: Fine-grained, replaceable components

Architectural Views

• Which views/perspectives are useful in designing and documenting a system?
• Suitable notations for describing architectural models?
• Each model shows one perspective of the system
• The model could show how the system is broken down into modules, interaction of runtime processes, different distribution approaches, etc

4+1 View Model of Software Architecture (Krutchén)

• Logical view: system as objects (requirements)
• Process view: interactions at run-time
• Development view: software decomposition for development
• Physical view: hardware and distribution
• User view complements the other four views

Architectural Patterns

• Patterns allow for knowledge representation, sharing, and reuse
• They're formalized descriptions of tried-and-true design practices across several environments
• Useful when/not useful information should be in the description
• Represented via tabular and graphical descriptions

Design Patterns (Categorization)

• Creational: Singleton, Factory, Builder, Prototype, Abstract Factory
• Structural: Adapter, Decorator, Facade, Composite, Proxy, Bridge
• Behavioral: Strategy, Template Method, Observer, Command, State, Visitor, Chain of Responsibility

UML: Basic Class

• Conceptual UML diagrams are shown
• Example includes the Car class with attributes (wheel count, running) and methods (startEngine, setSpeed)

UML: Directed Association

• Conceptual and example UML diagrams for showing object relationships are shown (Person, Car)

UML: Class Extension/Inheritance

• UML diagrams explain how a class extends or inherits from another (e.g., Fancy Car extending Car)

UML: Interface Implementation

• UML explanation of a class implementing an interface (example: Car implementing ICar)

UML Aggregations

• UML diagrams for aggregation relationships (e.g., Book in a Library)

UML Composition

• UML diagrams for composition relationships (e.g., Wings in an Aeroplane)

Creational Design Patterns (Introduction)

Singleton Pattern

• Singleton instance creation ensuring only one object exists
• Client application interacts to use the instance.

Singleton Pattern - Use Case

• Shows a leader board system where instances of the Leaderboard are shared across games

Prototype Pattern

• Cloning of objects is a focus of this pattern

Prototype Pattern - Use Case

• Shows how to clone records, especially when needed for reuse

Factory Pattern

• Use of factory classes to create objects

Factory Pattern - Use Case

• Shows chair creation using a ChairFactory

Builder Pattern

• This pattern allows the creation of complex objects step-by-step.
• Director class creates the builder and instructs it.

Builder Pattern - Use Case

• A use case shows creation of houses using directors (e.g., house type) and builders to ensure construction elements are set properly

This quiz covers the key concepts of architectural design in software engineering, including the design process, architectural views, and styles. It also explores the architecture of a packing robot control system, focusing on system components and their interactions. Test your understanding of these foundational topics in software architecture.