Software Architecture and Integration Quiz

Course Information

• Course name: Software Architecture
• Course code: BIS301
• Academic year: 2023
• Lecturer: Ian Sommerville

Introduction to System Analysis and Design

• Lecture notes contain material from Ian Sommerville.
• Focus on software architecture principles.

Software Architecture

• Essential for creating reliable, secure, and efficient software.
• Involves organization, decomposition into components, server organization, and technologies used.
• Different interpretations of 'software architecture':
  • As a noun (structure of a system)
  • As a verb (process of defining structures)
• IEEE definition of software architecture: the fundamental organization of a software system, embodied in its components, their relationships to each other and to the environment, and the principles guiding its design and evolution.

Software Architecture and Components

• Component: An element implementing a functionality or set of features.
• Software components can be collections of one or more services used by other components.
• Architectural design of software components should outline interfaces but not the implementation details.

Why is Architecture Important?

• Architecture fundamentally affects non-functional system properties.
• Architectural design involves understanding issues affecting the product's architecture and creating descriptions showing critical parts and their connections.
• Important to minimize system complexity for maintainability and to reduce mistakes when modifying or expanding systems.
• Increased complexity leads to more difficulty and cost understanding and changing a system and increases the likelihood of bugs and security vulnerabilities.

Non-Functional System Quality Attributes

• Responsiveness: Time taken to return results to users.
• Reliability: System's features functioning as expected.
• Availability: System's ability to deliver services when requested.
• Security: System's protection from unauthorized access.
• Usability: Ease of use for system users.
• Maintainability: Ease of updating and adding new features.
• Resilience: System's ability to continue delivering services in case of partial failure or outside attack.

Architecture of System Security

• Centralized security architecture: Storing all data in one secure location with a concentrated security effort, but makes compromising of the data more difficult when attacked by the enemy.
• Distributed security architecture: Distributes information across multiple locations. Makes compromising more difficult because it requires breaching security in many locations, compared to only one.

Centralized Security Architectures

• Easier to design and build security protection.
• Protected information accessible efficiently.
• Breaches lead to a loss of all protected information.
• Distribution of information makes protection more expensive and time-consuming.

Maintainability and Performance

• Shared database architecture: Two components (C1 and C2) use a common database. Changes to the common data need changes to both components.
• Multiple database architecture: Each component has its own database copy. Changes to one component's data do not affect others. However, multiple databases can lead to performance and implementation cost overhead.

Architectural Decisions

• Non-functional product characteristics (like security and performance) influence architectural choices.
• Product lifetime and software reuse constrain architectural choices.
• Number of users and compatibility with other software influence architectural choices.
• Balancing maintainability and performance, security and usability, availability and time-to-market during architectural decisions.

Trade-offs

• Maintainability vs. performance: Decomposing into small, independent components improves maintainability but may decrease performance due to increased communication between components.
• Security vs. usability: Layered security (e.g. Authentication, application, IP, etc.) makes for easier security but users might have to interact with additional security layers, reducing usability.
• Availability vs. time-to-market: Redundancy (multiple components working in parallel) improves availability but increases development time and cost.

Architectural Design Questions

• How components should be organized ?
• How components should be distributed and communicate?
• Which technologies to use and which components should be reused?
• Emphasize overall system functionality and consider how they deliver the required security, reliability and performance.

Component Organization

• Abstraction in software design focuses on essentials, ignoring unnecessary details.
• Architectural level focus on a larger scale architectural components.
• Decomposition analysis of components (breaking them down) into smaller, more manageable parts.
• Layered models are frequently used to depict a system's arrangement.

Architectural Models of Document Retrieval System

(Example diagrams showing a layered structure with different functionality in each layer, such as user interface, information retrieval, database management etc).

Architectural Complexity

• Increased system complexity stems from the number and relationships of system components.
• Local relationships between components are easier to understand than relationships spanning multiple modules or parts of the system.
• Architectural components that share dependencies can become complex, affecting both parties when modifications occur.
• Localizing data wherever possible minimizes dependencies (makes the system simpler.)

Architectural Design Guidelines

• Focus on single concerns for each component which creates a clear separation of responsibilities in the system.
• Stable component interfaces that change slowly lead to more maintenance-friendly systems.
• Implement functionality only once (avoid functional duplication)

Design Guidelines and Layered Architectures

• Each layer functions independently of other layers.
• Top layer is user interaction.
• Bottom layers provide general functionality which is reusable.
• Consistent component interaction within each layer.

Cross-Cutting Concerns

Cross-cutting concerns (i.e. security, performance and reliability): affect all layers in complex systems. Every layer in the system must take precautions for these cross-cutting concerns. Modifying one part of the system might cause unforeseen consequences in other parts making modification complex after the system is developed.

Technology Choices for Architecture

• Database choice (relational or NoSQL)
• Platform (web-based, mobile-app or both).
• Server system (in-house, cloud or both).
• Open source components.
• Development tools.

Database Types

• Relational Databases (SQL): Structured data in tables, suitable for predictable transactions.
• NoSQL Databases (e.g., MongoDB): Flexible data structures to store unstructured or semi-structured information and suitable for data analysis or big data.

Delivery Platform

• Web-based, mobile-based systems or a combination of both.
• Factors impacting the platform include intermittent connectivity issues, processor power, power management limitations and the usability concerns of touch screens and slower interactions with a system.

Architectures

• Server systems to run on a customer's server or a cloud system.
• Business products running on a cloud system may be more difficult or costly depending on concerns such as security.
• Cloud provider choice is part of designing system architecture.

Open Source

• Open-source software is readily available, modifiable.
• Reusability reduces development costs.
• Constraints: dependence on open-source components, license issues, and lack of control over evolution.
• Choice is driven by type of product, target audience and developer expertise.

Development Tools

• Development tools (e.g., mobile development toolkits, web application frameworks).
• Tool assumptions about system architecture that may be necessary to comply with in some systems.

iLearn Design Principles

• Design goals for the iLearn system: Adaptability, ease of updates with new learning tools.
• Components and services can be changed and replaced.
• Age appropriateness of user interfaces.
• Minimal effort required for users to make changes without affecting other users working on the system.

Designing iLearn as a Service-Oriented System

• Components of the system as services.
• Replaceability of components.
• Flexibility for different kinds of users (adaptability, etc) and interfaces.
• Full, partial, and independent service integration through APIs.

Distribution Architecture

• Client-server architectures (e.g. a web server provides a service to a client).
• Distributes different components and functionality across various servers.

Multi-Tier Client-Server Architecture

• Web server, application server, and database server.
• Each tier handles a specific task and reduces load by distributing it over various tiers.

Service-Oriented Architecture

• Stateless components that work on several computers.
• Replicated services improve resilience to failure or increase demand.

Issues in Architectural Choices

• Data types and updates: Single shared database or multiple.
• Change frequency (how often system components change), if components change regularly, having them as independent modules improves maintainability.
• System execution platform for the entire system running on customer systems or a cloud system.

Key Points

• Software architecture: Organization, relationships between components and principles.
• Non-functional characteristics (reliability, efficiency, and security).
• Architectural descriptions for development teams.
• System decomposition to create smaller components and improve management.
• Separating concerns, avoiding duplication and focusing on component interfaces, to make the system more maintainable.
• Common layered structures for web-based systems.
• Multi-tier, client-server and service-oriented architectures are frequently utilized.
• Important decisions about technologies, the cloud or in-house implementation.