ch6

Software Architecture Definitions

• Architecture is the fundamental organization of a system, including its components, their relationships, and governing principles for design and evolution (ANSI/IEEE Std 1471-2000).
• All software architecture is software design, but not all design is software architecture.
• Architecture is the first stage of the design process.

Architectural Design Decisions

• Is a generic application architecture suitable?
• How will the system be distributed?
• What architectural styles are appropriate?
• How will the system be structured?
• What method will decompose the system into modules?
• What control strategy should be implemented?
• How should the architectural design be evaluated?
• How should the architecture be documented?

Architecture Defines Structure

• Decomposes the system into components, modules, or subsystems.
• Defines component interfaces, detailing what a component can do.
• Defines component communications and dependencies.
• Outlines how components communicate.
• Specifies the responsibilities of each component.
• Clearly describes what each component will do when called upon.

Advantages of Explicit Architecture

• Facilitates stakeholder communication, using architecture as a discussion point.
• Enables system analysis to evaluate its non-functional requirements.
• Allows for large-scale reuse across various systems.
• Supports development of product-line architectures.

Quality Attribute Requirements

• Performance: Sub-four-second response times for 90% of requests.
• Security: All communications must be authenticated and encrypted using certificates.
• Resource Management: Server component runs on a low-end office server with 512MB memory.
• Usability: User interface runs in an internet browser to support remote users.
• Availability: 24/7/365 system operation with 0.99 overall availability.
• Reliability: No message loss with message delivery confirmations within 30 seconds.
• Scalability: Application handles a peak load of 500 concurrent users during the enrollment period.
• Modifiability: Architecture supports phased migration from current 4GL to .NET.

Constraints

• Business: Technology must integrate as a plug-in for MS BizTalk.
• Development: System must be written in Java.
• Schedule: First version delivery within six months.
• Business: Collaboration with MegaHugeTechCorp and leveraging their technology.

Structure and Dependencies

• Excessive component dependencies are undesirable.
• Identifying components prone to change is crucial.
• Minimizing direct dependencies on these components enhances the system's modifiability.

Coupling & Cohesion

• Lower Coupling: Minimize dependencies between components.
• Higher Cohesion: Design single-task components (responsibility).

Architecture Specifies Component Communication

• Communication involves function calls, RPCs (remote procedure calls), message passing (asynchronous), and synchronization to wait for reply.

Architecture is an Abstraction

• Provides an abstract view of design, hiding complexity.
• May not directly map architecture elements to software elements.
• Examples: Marketecture (informal depictions of structure, interactions, and design philosophies)
• Marketecture is easy to understand, promotes discussion, useful during design, review and sales process.

Marketecture Example

• A diagram illustrating ICDE repository, ICDE recording software, ICDE monitoring, internet, local information repositories, analysts, and third-party tools.

Decomposition

• Hierarchical decomposition is an effective abstraction approach.
• Components are allocated to development teams for partitioning.
• Architecture aims to lower coupling between clients and servers.
• Architecture seeks to attain high cohesion.

Philippe Krutchen - 4+1 View Model

• Logical View: Displays architecturally significant elements and their relationships.
• Process View: Highlights communication elements in the architecture.
• Physical View: How major processes/components are mapped to hardware.
• Development View: Shows internal software component organization.
• Architecture Use Cases: Specifies architecture requirements related to multiple views.

Architectural Patterns

• Reusable solutions to common problems in software architecture.
• Design Patterns: Apply to classes and relationships in code.
• Architectural Patterns: Focus on subsystems, components, and external systems.

N-Tier Client-Server Pattern

• Separates concerns (presentation, business logic, data).
• Uses synchronous communications (request-reply).
• Implements flexible deployment across tiers.

The Client-server pattern

• System organized into services delivered from separate servers.

• Clients access services for operations or data.

• Example: Film/video library with shared database.

• Advantages: Distributed services, variable load, broader accessibility

• Disadvantages: Single point of failure, potential network dependence, possible management issues if servers are owned by different entities.

Publish-Subscribe Pattern

• Many-to-many messaging, sending to all registered subscribers.
• Loose coupling, no direct binding between publishers and subscribers.

Pipe and Filter

• A simple architectural style connecting filters that process data streams.

• Each filter is connected to the next filter via a pipe for processing.

• Advantages: Easy understanding, supports transformation reuse.

• Disadvantages: Defining agreed-upon data formats for filter communication is essential.

The pipe and filter pattern

• Data processing is organized with distinct components (filters) transforming data.
• Data flows sequentially through these components.
• Advantages: Data transformation reuse is facilitated, and the workflow structure aligns with business processes.
• Disadvantages: There may be complexities when handling data formats, and communication overhead between filters can increase for non-compatible data.

Software Architecture Modeling; UML Component Diagram

• The diagram illustrates relationships between components, using UML component diagrams.

UML Communication Diagram

• This diagram illustrates interaction between components and objects in a system, using UML communication diagrams to show interactions.