What's the difference between design patterns and architectural patterns?

It requires a detailed explanation but I will try to sketch the differences to best of my knowledge.

Patterns are distilled commonality that you find in programs. It allows us to deconstruct a large complex structure and build using simple parts. It provides a general solution for a class of problems.

A large complex software goes through a series of deconstruction at different levels. At large level, architectural patterns are the tools. At smaller level, design patterns are the tools and at implementation level, programming paradigms are the tools.

A pattern can occur at very different levels. See Fractals. Quick sort, Merge sort are all algorithmic patterns for organizing a group of elements in a order.

For a most simplistic view:

Programming paradigms - specific to programming language

Design patterns - solves reoccurring problems in software construction

Architectural patterns - fundamental structural organization for software systems

Idioms are paradigm-specific and language-specific programming techniques that fill in low-level details.

Design patterns are usually associated with code level commonalities. It provides various schemes for refining and building smaller subsystems. It is usually influenced by programming language. Some patterns pale into insignificance due to language paradigms. Design patterns are medium-scale tactics that flesh out some of the structure and behavior of entities and their relationships.

While architectural patterns are seen as commonality at higher level than design patterns. Architectural patterns are high-level strategies that concerns large-scale components, the global properties and mechanisms of a system.

How are patterns obtained? Through:

re-use, classification and finally abstraction to distill the commonality.

If you have followed the thoughts laid above. You will see that Singleton is a "design pattern" while MVC is one of the "architectural" pattern to deal with separation of concerns.

Try reading on:

http://en.wikipedia.org/wiki/Architectural_pattern_(computer_science) http://en.wikipedia.org/wiki/Design_pattern http://en.wikipedia.org/wiki/Anti-pattern

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Design Patterns are well known patterns for solving technical problems in a way that has proven itself many times. Design patterns are common design structures and practices that make for creating reusable Object-Oriented software. Design pattern examples are Factory Pattern, Singleton, Facade, State, etc. Design patterns can be used to solve smaller problems throughout the application, and are much easier to inject, change, add than the overall architecture

architecture patterns are well known patterns for solving software application architecture problems. Software application architecture is the process of defining a structured solution that meets all of the technical and operational requirements. Application's architecture is the overall 'organization' of the code. Examples of different Architectures might be MVC, MVVM, MVP, n-layer (i.e. UI-BLL-DAL), etc. The architecture typically needs to be decided up front and often is difficult to change once the application is built.

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Well, for the main part it's a matter of the language. According to my experience the borderline between design and architecture, as far as software is concerned, is a broad river with it's width resulting from the water level which in turn is mainly influenced by the seasons of marketing. Generally the term "design" is used with a strong aspect of the software product's behavior as recognized by end users, whereas "architecture" stands for the technical structure of a software, i. e. the components, libraries, protocols and whatever it needs to fulfill the design. "Design patterns" take two roles: 1st they are regarded as best practices for solving a category of (more or less) standard problems, not prodiucts; 2nd they help the developers to communicate. Staying with your example of a Singleton, it allows us to know what the mechanics are about by just using the word, instead of explaining every time, that we created a single instance by using a designated dataspace (variable or whatever) which is set in a controlled manner and is guaranteed to be the only one, because we protected the constructor of the class etc. So IMHO the short answer to your question is: It depends on who is talking. Does that make some sense?

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Architectural elements tend towards collections of classes or modules, generally represented as boxes. Diagrams about architecture represent the loftiest level looking down, whereas class diagrams are at the most atomic level. The purpose of architecture patterns is to understand how the major parts of the system fit together, how messages and data flow through the system, and other structural concerns. Architecture patterns utilize a variety of component types, each typically composed of successively smaller modules. Each component has a responsibility within the architecture Design patterns are low level or class level design patterns for smaller particles of applications.

For more information: https://www.oreilly.com/ideas/contrasting-architecture-patterns-with-design-patterns

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Design Patterns differ from Architectural Patterns in their scope, they are more localized, they have less impact on the code base, they impact a specific section of the code base, for example:

How to instantiate an object when we only know what type needs to be instantiated at run time (maybe a Factory Class?)
How to make an object behave differently according to its state (maybe a state machine, or a Strategy Pattern?)

Architectural Patterns have an extensive impact on the code base, most often impacting the whole application either horizontally (ie. how to structure the code inside a layer) or vertically (ie. how a request is processed from the outer layers into the inner layers and back). Examples of Architectural Patterns: Model-View-Controller, Model-View-ViewModel

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If i put this very simply

Architecture governs data flow in app i.e. how the data flows between various components in app

Design Pattern deals with any destruct you apply to break a large unit into manageable chunks

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