Architecture Styles & Patterns

 One thing is very clear: Design Patterns are design patterns not Architecture Styles or Architecture Patterns. What is not clearly standardized is Architecture Style versus Architecture Patterns. Even if you try to define them based on the fundamental difference between style and pattern, you see same name is used in Architecture Style and Architecture Pattern as well. However to make things easier let us consider following:

The distinction between architectural styles and patterns is often context-dependent rather than strictly defined.

Styles focus on structural organization, while patterns offer problem-solving approaches within that structure.

Many of the fundamental architectural styles from Shaw & Garlan are later categorized as patterns by Bass et al.

Architectural Style

An architectural style defines a high-level structural organization of a software system. It provides a general framework for system design, including common component types and their interactions. Architectural styles help guide the system's structure but do not specify detailed implementation.

Historical Context:

• The concept of architectural styles was discussed extensively in the 1990s by Mary Shaw and David Garlan in Software Architecture: Perspectives on an Emerging Discipline.
• Architectural styles represent recurring, well-known ways to organize software systems.

🔹 Examples of Architectural Styles:

1. Layered Architecture – Used in OS design, enterprise applications, web applications (e.g., MVC).
2. Client-Server – Found in database systems, email, and networked applications.
3. Microservices – Modern cloud-based applications (Netflix, Amazon, Uber).
4. Event-Driven Architecture – Used in IoT systems, real-time analytics, messaging platforms.

Architectural Pattern

An architectural pattern provides a solution to common architectural problems by defining how different components should interact. Unlike architectural styles, which focus on system structure, architectural patterns define specific design decisions to address challenges like scalability, security, or fault tolerance.

Historical Context:

• Len Bass et al. introduced architectural patterns in Software Architecture in Practice.
• Architectural patterns emerged to standardize and solve architectural problems that arise in different contexts.
• Unlike GOF (Gang of Four) design patterns, which apply to low-level software design, architectural patterns address system-wide concerns.

🔹 Examples of Architectural Patterns:

1. Model-View-Controller (MVC) – Used in web frameworks (Django, Spring MVC, Angular).
2. Broker Pattern – Found in middleware, message brokers (RabbitMQ, Apache Kafka).
3. Microkernel Pattern – Used in extensible applications (Eclipse, VS Code).
4. Pipe and Filter – Found in Unix shell pipelines, ETL processes.

Architectural Styles from Shaw & Garlan (1996)

In Software Architecture: Perspectives on an Emerging Discipline, Shaw & Garlan outlined common software architectural styles, including:

1. Layered Architecture
2. Pipe and Filter
3. Client-Server
4. Event-Based (Implicit Invocation)
5. Repository (Blackboard)
6. Interpreter (Virtual Machine)
7. Process Control

Architectural Patterns from Bass et al. (1998, 2003, 2012 editions of Software Architecture in Practice)

Len Bass et al. define architectural patterns that overlap with the above styles, including:

1. Layered Pattern (equivalent to Layered Architecture)
2. Microkernel Pattern (similar to Interpreter Architecture)
3. Client-Server Pattern (same as Client-Server Architecture)
4. Event-Bus Pattern (matches Event-Based Architecture)
5. Blackboard Pattern (similar to Repository Architecture)
6. Pipe-and-Filter Pattern (directly corresponds to Pipe-and-Filter Architecture)