[architecture] Software Design vs. Software Architecture

Could someone explain the difference between Software Design and Software Architecture?

More specifically; if you tell someone to present you the 'design' - what would you expect them to present? Same goes for 'architecture'.

My current understanding is:

• Design: UML diagram/flow chart/simple wireframes (for UI) for a specific module/part of the system
• Architecture: component diagram (showing how the different modules of the system communicates with each other and other systems), what language is to be used, patterns...?

Correct me if I'm wrong. I have referred Wikipedia has articles on http://en.wikipedia.org/wiki/Software_design and http://en.wikipedia.org/wiki/Software_architecture, but I'm not sure if I have understood them correctly.

Personally, I like this one:

"The designer is concerned with what happens when a user presses a button, and the architect is concerned with what happens when ten thousand users press a button."

SCEA for Java™ EE Study Guide by Mark Cade and Humphrey Sheil

...long time ago in a faraway place philosophers worried about the distinction between the one and the many. Architecture is about relationship, which requires the many. Architecture has components. Design is about content, which requires the one. Design has properties, qualities, characteristics. We typically think that design is within architecture. Dualistic thinking gives the many as primordial. But architecture is also within design. It's all how we choose to view what is before us - the one or the many.

Pretty subjective but my take:

Architecture The overall design of the system including interactions with other systems, hardware requirement, overall component design, and data flow.

Design The organization and flow of a component in the overall system. This would also include the component's API for interaction with other components.

1. Architecture means the conceptual structure and logical organization of a computer or computer-based system.

   Design means a plan or drawing produced to show the look and function or workings of a system or an object before it is made.

2. If you are “architecting” a component, you are defining how it behaves in the larger system.

   If you are “designing” the same component, you are defining how it behaves internally.

All architecture is design but NOT all design is architecture.

What part is the Design, the How is the concrete implementation and the intersection of What and How is Architecture.

Image for differentiating Architecture and Design:

There are also design decisions, that are not architecturally significant, i.e. does not belongs to the architecture branch of design. For example, some component’s internal design decisions, like- choice of algorithm, selection of data structure etc.

Any design decision, which isn’t visible outside of its component boundary is a component’s internal design and is non-architectural. These are the design decisions a system architect would leave on module designer’s discretion or the implementation team as long as their design don’t break the architectural constraints imposed by the system level architecture.

The link that gives good analogy

Architecture are "the design decisions that are hard to change."

After working with TDD, which practically means that your design changes all the time, I often found myself struggling with this question. The definition above is extracted from Patterns of Enterprise Application Architecture, By Martin Fowler

It means that the architecture depends on the Language, Framework and the Domain of your system. If your can just extract an interface from your Java Class in 5 minutes it is no longer and architecture decision.

Good question... Although the line between them is hardly a bright sharp line, imho, if you are using both terms, then Architecture encompasses more technical or structural decisions about how to build or construct something, especially those decisions that will be hard (or harder) to change once implemeneted, whereas Design encompasses those decisions that either are easy to change later (like method names, class <-> file organizational structure, design patterns, whether to use a singleton or a static class to solve some specific problem, etc. ) and/or those that effect the appearance or esthetic aspects of a system or application (Human Interface, ease of use, look and feel, etc.)

The software architecture of a program or computing system is the structure or structures of the system, which comprise software components, the externally visible properties of those components, and the relationships between them.

(from Wikipedia, http://en.wikipedia.org/wiki/Software_architecture)

Software design is a process of problem-solving and planning for a software solution. After the purpose and specifications of software are determined, software developers will design or employ designers to develop a plan for a solution. It includes low-level component and algorithm implementation issues as well as the architectural view.

(from Wikipedia, http://en.wikipedia.org/wiki/Software_design)

Couldn't have said it better myself :)

Architecture is strategic, while Design is tactical.

Architecture comprises the frameworks, tools, programming paradigms, component-based software engineering standards, high-level principles..

While design is an activity concerned with local constraints, such as design patterns, programming idioms, and refactorings.

As others also pointed out, laying out the architecture of a piece of software is actually taking the major design decisions which have overall influence over the software development or execution life-cycle; so simplistically architecture is just high level design.

Even if an architecture decision does not affect all components (is thus, local) it must still be globally relevant, i.e. it impacts the whole system in some way; otherwise is simply a local design decision.

What I'd like to point out though, that a more relevant question related to architecture might be Architecture vs Organization as defined by Hennessy & Patterson in Computer Architecture. Based on this we could think about architecture as the data model (input/output, state) abstraction of the system and the organization as the typical design decisions taken during the implementation (software development) process.

My reminder:

• We can change the Design without asking someone
• If we change the Architecture we need to communicate it to someone (team, client, stakeholder, ...)

Yep that sounds right to me. The design is what you're going to do, and architecture is the way in which the bits and pieces of the design will be joined together. It could be language agnostic, but would normally specify the technologies to be used ie LAMP v Windows, Web Service v RPC.

Architecture:
Structural design work at higher levels of abstraction which realize technically significant requirements into the system. The architecture lays down foundation for further design.

Design:
The art of filling in what the architecture does not through an iterative process at each layer of abstraction.

There is no definitive answer to this because "software architecture" and "software design" have quite a number of definitions and there isn't a canonical definition for either.

A good way of thinking of it is Len Bass, Paul Clements and Rick Kazman's statement that "all architecture is design but not all design is architecture" [Software Architecture in Practice]. I'm not sure I quite agree with that (because architecture can include other activities) but it captures the essence that architecture is a design activity that deals with the critical subset of design.

My slightly flippant definition (found on the SEI definitions page) is that it's the set of decisions which, if made wrongly, cause your project to get cancelled.

A useful attempt at separating architecture, design and implementation as concepts was done by Amnon Eden and Rick Kazman some years ago in a research paper entitled "Architecture, Design, Implementation" which can be found here: http://www.sei.cmu.edu/library/assets/ICSE03-1.pdf. Their language is quite abstract but simplistically they say that architecture is design that can be used in many contexts and is meant to be applied across the system, design is (err) design that can be used in many contexts but is applied in a specific part of the system, and implementation is design specific to a context and applied in that context.

So an architectural decision could be a decision to integrate the system via messaging rather than RPC (so it's a general principle that could be applied in many places and is intended to apply to the whole system), a design decision might be to use a master/slave thread structure in the input request handling module of the system (a general principle that could be used anywhere but in this case is just used in one module) and finally, an implementation decision might be to move responsibilities for security from the Request Router to the Request Handler in the Request Manager module (a decision relevant only to that context, used in that context).

I hope this helps!

I view architecture as Patrick Karcher does - the big picture. For example, you can provide the architecture to a building, view its structural support, the windows, entries and exits, water drainage, etc. But you have not "designed" the floor layout's, cubicle positions etc.

So while you've architected the building you have not designed the layout of each office. I think the same holds true for software.

You could view designing the layout, as "architecting the layout" though ...

In My opinion , Architecture is nothing but a vision ,gathering requirements and framing the building blocks in right way

where as design , to construct particular block there are 100 solutions may be available, but to meet exact requirement we need to choose the right method , so choosing right method or algorithm is nothing but design

Software design has a longer history while the term software architecture is barely 20 years old. Hence, it is going through growing pains right now.

Academics tend to see Architecture as part of the larger field of software design. Although there is growing recognition that Arch is a field within it's own.

Practitioners tend to see Arch as high-level design decisions that are strategic and can be costly in a project to undo.

The exact line between Arch and design depends on the software domain. For instance, in the domain of Web Applications, the layered architecture is gaining the most popularity currently (Biz Logic Layer, Data Access Layer, etc.) The lower level parts of this Arch are considered design (class diagrams, method signatures, etc.) This would be defined differently in the domains of embedded systems, operating systems, compilers, etc.

Software architecture is best used at the system level, when you need to project business and functions identify by higher architecture levels into applications.

For instance, your business is about "Profit and Loss" for traders, and your main functions involved "portfolio evaluation" and "risk computation".

But when a Software Architect will details his solution, he will realize that:

"portfolio evaluation" can not be just one application. It needs to be refined in manageable projects like:

• GUI
• Launcher
• Dispatcher
• ...

(because the operations involved are so huge they need to be split between several computers, while still being monitored at all times through a common GUI)

a Software design will examine the different applications, their technical relationship and their internal sub-components.
It will produce the specifications needed for the last Architecture layer (the "Technical Architecture") to work on (in term of technical framework or transversal components), and for the project teams (more oriented on the implementation of the business functions) to begin their respective projects.

if somebody constructs a ship, then engine, hull, electric-circuits etc. will be his "architectural elements". For him, engine-construction will be "design work".

If he then delegates the construction of the engine to another team, they will create an "engine architecture"...

So - it depends on the level of abstraction or detail. One persons' architecture might be anothers' design!

Architecture is design, but not all design is architectural. Therefore, strictly speaking, it would make more sense to try to differentiate between architectural design and non-architectural design. And what is the difference? It depends! Each software architect may have a different answer (ymmv!). We develop our heuristics to come up with an answer, such as 'class diagrams are architecture and sequence diagrams are design'. See DSA book for more.

It's common to say that architecture is at a higher abstraction level than design, or architecture is logical and design is physical. But this notion, albeit commonly accepted, is in practice useless. Where do you draw the line between high or low abstraction, between logical and physical? It depends!

So, my suggestion is:

• create a single design document.
• name this design document the way you want or, better, the way the readers are more accustomed to. Examples: "Software Architecture", "Software Design Specification".
• break this document into views and keep in mind you can create a view as a refinement of another view.
• make the views in the document navigable by adding cross-references or hyperlinks
• then you'll have higher level views showing broad but shallow overview of the design, and closer-to-implementation views showing narrow but deeper design details.
• you may want to take a look at an example of multi-view architecture document (here).

Having said all that... a more relevant question we need to ask is: how much design is enough? That is, when should I stop describing the design (in diagrams or prose) and should move on to coding?

Architecture and design are closely related; the main difference between them is really about which way we face. Architecture faces towards strategy, structure and purpose, towards the abstract. Design faces towards implementation and practice, towards the concrete.

Software architecture is“concerned with issues...beyond the algorithms and data structures of the computation.

Architecture is specifically not about…details of implementations (e.g., algorithms and data structures.) Architectural design involves a richer collection of abstractions than is typically provided by OOD” (object-oriented design).

Design is concerned with the modularization and detailed interfaces of the design elements, their algorithms and procedures, and the data types needed to support the architecture and to satisfy the requirements.

“architecture” is often used as a mere synonym for “design” (sometimes preceded with the adjective “high-level”). And many people use the term “architectural patterns” as a synonym for “design patterns.”

Check out this link.

Defining the Terms Architecture, Design, and Implementation

I found this as I was looking for simple distinction between architecture and design myself;
What do you think of this way of looking at them:

• architecture is "what" we're building;
• design is "how" we're building;

http://jinwolf.tumblr.com/post/6591954772/architectural-patterns-vs-design-patterns

The architecture tells you how your system is laid out. One traditional architectural pattern example is 3 tier system where your system is broken down into presentation, business and data layers.

The domain driven design promotes 4 tier architecture. Presentation, application, domain and infrastructure layers. And the repository pattern resides in between the domain layer and infrastructure layer. Your domain models should not know anything about the infrastructure and also should be kept pure and independent from it as well. That is why we have the repository to mediate those two layers.

The repository pattern is still a pattern since it's a reusable solution and handles the problems that repeats. However, the repository pattern becomes only relevant when we talk about the architecture. It has its roles and responsibilities in the domain driven design architecture. It is not mathematical type general solution such as the abstract factory pattern which can be applied anywhere in your system.

Architecture is high level, abstract and logical design whereas software design is low level,detailed and physical design.

Design: To learn about the modules, what kind of relationships between the modules, functionality of each module, Classes and its member functions, interfaces of each module that communicating with each other.

Architecture: Architecture is the whole entire structure of a software system. All the modules, classes and components perform different tasks and will give a unique result.

For Example: There is a home which has 5 rooms. There are attach bathrooms as well. Kitchen is also there in the home. So there are different things in the home and these all things have different relationships between each other. So this is all about the 'DESIGN' of a home.

While when you are looking from outside of a house the whole structure you are looking at is all about the Architecture.

Cliff Notes version:

Design: Implementing a solution based on the specifications of the desired product.

Architecture: The foundation/tools/infrastructure/components that support your design.

This is a pretty broad question that will invoke a lot of responses.

Following are the references that may explain Architecture in more detail and a list of UML diagrams for software architecture. (I could not find listing of UML diagrams for software design )

Grady Booch

UML 2 Diagram use for Architectural Models

Classification of UML diagrams

Classification of UML diagrams

Even after posting this answer, i myself is not clear which diagram is for architecture and which one for design :). Grady Booch, in his slide # 58, states that Classes, Interfaces and Collaborations are part of Design View and this Design View is one of the View of Architecture !!!

In some descriptions of the SDLC (Software Development Life Cycle) they are interchangeable, but the consesus is that they are distinct. They are at the same time: different (1) stages, (2) areas of responsibility, and (3) levels of decision-making.

• Architecture is the bigger picture: the choice of frameworks, languages, scope, goals, and high-level methodologies (Rational, waterfall, agile, etc.).
• Design is the smaller picture: the plan for how code will be organized; how the contracts between different parts of the system will look; the ongoing implementation of the project's methodologies and goals. Specification are written during this stage.

These two stages will seem to blend together for different reasons.

1. Smaller projects often don't have enough scope to separate out planning into these to stages.
2. A project might be a part of a larger project, and hence parts of both stages are already decided. (There are already existing databases, conventions, standards, protocols, frameworks, reusable code, etc.)
3. Newer ways of thinking about the SDLC (see Agile methodologies) somewhat rearrange this traditional approach. Design (architecture to a lesser extent) takes place throughout the SDLC on purpose. There are often more iterations where the whole process happens over and over.
4. Software development is complicated and difficult to plan anyway, but clients/managers/salespeople usually make it harder by changing goals and requirements mid-stream. Design and even architectural decisions must bemade later in the project whether that is the plan or not.

Even if the stages or areas of responsibility blend together and happen all over the place, it is always good to know what level of decision-making is happening. (We could go on forever with this. I'm trying to keep it a summary.) I'll end with: Even if it seems your project has no formal architectural or design stage/AOR/documentaiton, it IS happening whether anyone is consciously doing it or not. If no one decides to do architecture, then a default one happens that is probably poor. Ditto for design. These concepts are almost more important if there are no formal stages representing them.

I think architecture is about the interfaces to humans and/or systems. For insance a web service contract, including protocols and so on, is architecture. How a screen is composed, not colors and such but what fields are there, is architecture.

Design is how something is to be built. What frameworks, language, technology etc. This must of course be aligned with enterprise guidelines and restrictions considering platforms, security and so on.

ARCHITECTURE:- An architecture creats the plans layout in various stages of the constructions as acording to the specifications.

DESINER:- A desiner is activity that it fullfil all the essential requirments of the archecture plans with the functional,asthetectic & appreance to the layouts.

Architecture is design with a rationale that comes from various factors the most important of which are the non-functional requirements like say scalability and certainly not the least is experience. Without rationale you are left with plain pattern, or how to do. Whether designing at a higher level or at the class level its still design.

OR put another way

Architecture is meta-design, i.e. designing the design. You have a few patterns that are known to fit a certain solution space, which would you select and why? Architecture is when you answer the "which" and "why" (the "how" is already given by design). It certainly does not depend on level of abstraction, for example implementing distributed sessions is not a class level task, but there are a few designs from which to select for a given architecture.

Likewise, architecture is reflected even in a class level design. Under a scalable architecture, class design is often different if you were to do it without the scalability factor in mind. Why you must have a method "BeginAsyncUpload" versus "Upload" is an architectural decision.

Interestingly, as we move focus towards system element at the higher level the questions "which and why" become more important and "how" becomes less relevant. Moving in the other direction the "how" part becomes more important, also because repeated usage makes it obvious, for example, to select between Abstract Factory or Prototype.

I really liked this paper for a rule of thumb on separating architecture from design:

http://www.eden-study.org/articles/2006/abstraction-classes-sw-design_ieesw.pdf

It's called the Intension/Locality hypothesis. Statements on the nature of the software that are non-local and intensional are architectural. Statements that are local and intensional are design.

Architecture is the resulting collection of design patterns to build a system.

I guess Design is the creativity used to put all this together?

Architecture identifies fundamental components of the system, describes their organisation and how they are related to create a framework for the system.

Design describes various components and how they should be developed to provide required functionality with in the framework provided by the system architecture.

Architecture is more like integrating various functionalities of a System to achive one goal of the System as a whole, while design addresses each functional requirements.

For example, take example of MVVM, which is an architectural pattern. For notification functionality, MVVM uses observer Pattern, which in turn is a design pattern,

Also, refer to: http://en.wikipedia.org/wiki/4%2B1_Architectural_View_Model

I think we should use the following rule to determine when we talk about Design vs Architecture: If the elements of a software picture you created can be mapped one to one to a programming language syntactical construction, then is Design, if not is Architecture.

So, for example, if you are seeing a class diagram or a sequence diagram, you are able to map a class and their relationships to an Object Oriented Programming language using the Class syntactical construction. This is clearly Design. In addition, this might bring to the table that this discussion has a relation with the programming language you will use to implement a software system. If you use Java, the previous example applies, as Java is an Object Oriented Programming Language. If you come up with a diagram that shows packages and its dependencies, that is Design too. You can map the element (a package in this case) to a Java syntactical construction.

Now, suppose your Java application is divided in modules, and each module is a set of packages (represented as a jar file deployment unit), and you are presented with a diagram containing modules and its dependencies, then, that is Architecture. There isn’t a way in Java (at least not until Java 7) to map a module (a set of packages) to a syntactical construction. You might also notice that this diagram represents a step higher in the level of abstraction of your software model. Any diagram above (coarse grained than) a package diagram, represents an Architectural view when developing in the Java programming language. On the other hand, if you are developing in Modula-2, then, a module diagram represents a Design.

(A fragment from http://www.copypasteisforword.com/notes/software-architecture-vs-software-design)

I like Roy Thomas Fielding's definition and explanation about what is software architecture in his paper: Architectural Styles and the Design of Network-based Software Architectures

A software architecture is an abstraction of the run-time elements of a software system during some phase of its operation. A system may be composed of many levels of abstraction and many phases of operation, each with its own software architecture.

He emphasizes "run-time elements" and "levels of abstraction".

I'd say you are right, in my own words;

Architecture is the allocation of system requirements to system elements. Four statements about an architecture:

1. It can introduce non-functional requirements like language or patterns.
2. It defines the interaction between components, interfaces, timing, etc.
3. It shall not introduce new functionality,
4. It allocates the (designed) functions that the system is intended to perform to elements.

Architecture is an essential engineering step when a complexity of the system is subdivided.

Example: Think about your house, you don't need an architect for your kitchen (only one element involved) but the complete building needs some interaction definitions, like doors, and a roof.

Design is a informative representation of the (proposed) implementation of the function. It is intended to elicit feedback and to discuss with stakeholders. It might be good practice but is not an essential engineering step.

It would be nice to see the kitchen design see before the kitchen is installed but it is not essential for the cooking requirement:

If I think about it you can state:

• architecture is for a public/engineers on a more detailed abstraction level
• design is intended for public on a less detailed abstraction level

I agree with many of the explanations; essentially we are recognizing the distinction between the architectural design and the detailed design of the software systems.

While the goal of the designer is to be as precise and concrete in the specifications as it will be necessary for the development; the architect essentially aims at specifying the structure and global behavior of the system just as much as required for the detailed design to begin with.

A good architect will prevent hyper-specifications - the architecture must not be overly specified but just enough, the (architectural) decisions established only for the aspects that present costliest risks to handle, and effectively provide a framework ("commonality") within which the detailed design can be worked upon i.e. variability for local functionality.

Indeed, the architecture process or life-cycle just follows this theme - adequate level of abstraction to outline the structure for the (architecturally) significant business requirements, and leave more details to the design phase for more concrete deliverables.