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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..?

Tutorial in PDF - You can download the PDF of this wonderful tutorial by paying a nominal price of $9.99. Your contribution will go a long way in helping us serve. Software design. In October 2003, he attended a National Science Foundation (NSF) workshop in Virginia on the “Science of design”. Fred Brookes, “We don’t know what we’re doing, and we don’t know what we’ve done” Software design process is an art or an inexact science. . The software design process involves gaining knowledge about a problem, and about its technical solution. We describe both the problem and the solution in a series of design models. Testing, manipulating and transforming those models helps us gather more knowledge. One of the most detailed models is written in. In the Software Design and Architecture Specialization, you will learn how to apply design principles, patterns, and architectures to create reusable and flexible software applications and systems. You will learn how to express and document the design and architecture of a software system using a. . Software Architecture - Zheng Qin, Jiankuan Xing, Xiang Zheng. Garfixia Software Architecture - Patrick Van Bergen. Art of Software Architecture: Design methods and Techniques - S.T.

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.

user3956566Mads MobækMads Mobæk

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41 Answers

You're right yes. The architecture of a system is its 'skeleton'. It's the highest level of abstraction of a system. What kind of data storage is present, how do modules interact with each other, what recovery systems are in place. Just like design patterns, there are architectural patterns: MVC, 3-tier layered design, etc.

Software design is about designing the individual modules / components. What are the responsibilities, functions, of module x? Of class Y? What can it do, and what not? What design patterns can be used?

So in short, Software architecture is more about the design of the entire system, while software design emphasizes on module / component / class level.

Robert HarveyRazzieRazzie

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.

Patrick KarcherPatrick Karcher

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.

Chris KannonChris Kannon

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;

Bo Persson

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

TryinHardTryinHard

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

andand

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, ..)

Peter GfaderPeter Gfader

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)

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

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.

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?

Paulo MersonPaulo Merson

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.

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 :)

Larry WatanabeLarry Watanabe

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 ..

mr-skmr-sk

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.)

Charles BretanaCharles Bretana

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.

TeboTebo

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.

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

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.

..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:

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

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

ErikEJesse VogtJesse Vogt

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.

VonCVonC

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 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.

ekerenekeren

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.

kd7kd7

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

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

Mark RedmanMark Redman

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.

LeWoodyLeWoody

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

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

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'.

JackyJacky

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!

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Glossaries

Software architecture refers to the fundamental structures of a software system and the discipline of creating such structures and systems. Each structure comprises software elements, relations among them, and properties of both elements and relations.^[1] The architecture of a software system is a metaphor, analogous to the architecture of a building.^[2] It functions as a blueprint for the system and the developing project, laying out the tasks not necessary to be executed by the design teams.^[3]

Software architecture is about making fundamental structural choices that are costly to change once implemented. Software architecture choices include specific structural options from possibilities in the design of software. For example, the systems that controlled the space shuttle launch vehicle had the requirement of being very fast and very reliable. Therefore, an appropriate real-time computing language would need to be chosen. Additionally, to satisfy the need for reliability the choice could be made to have multiple redundant and independently produced copies of the program, and to run these copies on independent hardware while cross-checking results.

Documenting software architecture facilitates communication between stakeholders, captures early decisions about the high-level design, and allows reuse of design components between projects.^[4]:29–35

• 5Architecture activities
• 6Software architecture topics
• 7Related fields

Scope[edit]

Opinions vary as to the scope of software architectures:^[5]

• Overall, macroscopic system structure;^[6] this refers to architecture as a higher level abstraction of a software system that consists of a collection of computational components together with connectors that describe the interaction between these components.
• The important stuff—whatever that is;^[7] this refers to the fact that software architects should concern themselves with those decisions that have high impact on the system and its stakeholders.
• That which is fundamental to understanding a system in its environment'^[8]
• Things that people perceive as hard to change;^[7] since designing the architecture takes place at the beginning of a software system's lifecycle, the architect should focus on decisions that 'have to' be right the first time. Following this line of thought, architectural design issues may become non-architectural once their irreversibility can be overcome.
• A set of architectural design decisions;^[9] software architecture should not be considered merely a set of models or structures, but should include the decisions that lead to these particular structures, and the rationale behind them. This insight has led to substantial research into software architecture knowledge management.^[10]

There is no sharp distinction between software architecture versus design and requirements engineering (see Related fields below). They are all part of a 'chain of intentionality' from high-level intentions to low-level details.^[11]:18

Characteristics[edit]

Software architecture exhibits the following:

Multitude of stakeholders: software systems have to cater to a variety of stakeholders such as business managers, owners, users, and operators. These stakeholders all have their own concerns with respect to the system. Balancing these concerns and demonstrating how they are addressed is part of designing the system.^[4]:29–31 This implies that architecture involves dealing with a broad variety of concerns and stakeholders, and has a multidisciplinary nature.

Separation of concerns: the established way for architects to reduce complexity is to separate the concerns that drive the design. Architecture documentation shows that all stakeholder concerns are addressed by modeling and describing the architecture from separate points of view associated with the various stakeholder concerns.^[12] These separate descriptions are called architectural views (see for example the 4+1 Architectural View Model).

Quality-driven: classic software design approaches (e.g. Jackson Structured Programming) were driven by required functionality and the flow of data through the system, but the current insight^[4]:26–28 is that the architecture of a software system is more closely related to its quality attributes such as fault-tolerance, backward compatibility, extensibility, reliability, maintainability, availability, security, usability, and other such –ilities. Stakeholder concerns often translate into requirements on these quality attributes, which are variously called non-functional requirements, extra-functional requirements, behavioral requirements, or quality attribute requirements.

Recurring styles: like building architecture, the software architecture discipline has developed standard ways to address recurring concerns. These 'standard ways' are called by various names at various levels of abstraction. Common terms for recurring solutions are architectural style,^{[11]:273–277} tactic,^[4]:70–72reference architecture^[13][14] and architectural pattern.^{[4]:203–205}

Conceptual integrity: a term introduced by Fred Brooks in The Mythical Man-Month to denote the idea that the architecture of a software system represents an overall vision of what it should do and how it should do it. This vision should be separated from its implementation. The architect assumes the role of 'keeper of the vision', making sure that additions to the system are in line with the architecture, hence preserving conceptual integrity.^[15]:41–50

Cognitive constraints:an observation first made in a 1967 paper by computer programmer Melvin Conway that organizations which design systems are constrained to produce designs which are copies of the communication structures of these organizations. As with conceptual integrity, it was Fred Brooks who introduced it to a wider audience when he cited the paper and the idea in his elegant classic The Mythical Man-Month, calling it 'Conway's Law.'

Motivation[edit]

Software architecture is an 'intellectually graspable' abstraction of a complex system.^[4]:5–6 This abstraction provides a number of benefits:

Software Architecture Design Methodology And Styles Pdf

• It gives a basis for analysis of software systems' behavior before the system has been built.^[2] The ability to verify that a future software system fulfills its stakeholders' needs without actually having to build it represents substantial cost-saving and risk-mitigation.^[16] A number of techniques have been developed to perform such analyses, such as ATAM.
• It provides a basis for re-use of elements and decisions.^[2][4]:35 A complete software architecture or parts of it, like individual architectural strategies and decisions, can be re-used across multiple systems whose stakeholders require similar quality attributes or functionality, saving design costs and mitigating the risk of design mistakes.
• It supports early design decisions that impact a system's development, deployment, and maintenance life.^[4]:31 Getting the early, high-impact decisions right is important to prevent schedule and budget overruns.
• It facilitates communication with stakeholders, contributing to a system that better fulfills their needs.^[4]:29–31 Communicating about complex systems from the point of view of stakeholders helps them understand the consequences of their stated requirements and the design decisions based on them. Architecture gives the ability to communicate about design decisions before the system is implemented, when they are still relatively easy to adapt.
• It helps in risk management. Software architecture helps to reduce risks and chance of failure.^[11]:18
• It enables cost reduction. Software architecture is a means to manage risk and costs in complex IT projects.^[17]

History[edit]

The comparison between software design and (civil) architecture was first drawn in the late 1960s,^[18] but the term software architecture became prevalent only in the beginning of the 1990s.^[19]The field of computer science had encountered problems associated with complexity since its formation.^[20] Earlier problems of complexity were solved by developers by choosing the right data structures, developing algorithms, and by applying the concept of separation of concerns. Although the term 'software architecture' is relatively new to the industry, the fundamental principles of the field have been applied sporadically by software engineering pioneers since the mid-1980s. Early attempts to capture and explain software architecture of a system were imprecise and disorganized, often characterized by a set of box-and-line diagrams.^[21]

Software architecture as a concept has its origins in the research of Edsger Dijkstra in 1968 and David Parnas in the early 1970s. These scientists emphasized that the structure of a software system matters and getting the structure right is critical. During the 1990s there was a concerted effort to define and codify fundamental aspects of the discipline, with research work concentrating on architectural styles (patterns), architecture description languages, architecture documentation, and formal methods.^[22]

Research institutions have played a prominent role in furthering software architecture as a discipline. Mary Shaw and David Garlan of Carnegie Mellon wrote a book titled Software Architecture: Perspectives on an Emerging Discipline in 1996, which promoted software architecture concepts such as components, connectors, and styles. The University of California, Irvine's Institute for Software Research's efforts in software architecture research is directed primarily in architectural styles, architecture description languages, and dynamic architectures.

IEEE 1471-2000, Recommended Practice for Architecture Description of Software-Intensive Systems, was the first formal standard in the area of software architecture. It was adopted in 2007 by ISO as ISO/IEC 42010:2007. In November 2011, IEEE 1471–2000 was superseded by ISO/IEC/IEEE 42010:2011, Systems and software engineering – Architecture description (jointly published by IEEE and ISO).^[12]

While in IEEE 1471, software architecture was about the architecture of 'software-intensive systems', defined as 'any system where software contributes essential influences to the design, construction, deployment, and evolution of the system as a whole', the 2011 edition goes a step further by including the ISO/IEC 15288 and ISO/IEC 12207 definitions of a system, which embrace not only hardware and software, but also 'humans, processes, procedures, facilities, materials and naturally occurring entities'. This reflects the relationship between software architecture, enterprise architecture and solution architecture.

Architecture activities[edit]

There are many activities that a software architect performs. A software architect typically works with project managers, discusses architecturally significant requirements with stakeholders, designs a software architecture, evaluates a design, communicates with designers and stakeholders, documents the architectural design and more.^[23] There are four core activities in software architecture design.^[24] These core architecture activities are performed iteratively and at different stages of the initial software development life-cycle, as well as over the evolution of a system.

Architectural analysis is the process of understanding the environment in which a proposed system or systems will operate and determining the requirements for the system. The input or requirements to the analysis activity can come from any number of stakeholders and include items such as:

• what the system will do when operational (the functional requirements)
• how well the system will perform runtime non-functional requirements such as reliability, operability, performance efficiency, security, compatibility defined in ISO/IEC 25010:2011 standard^[25]
• development-time non-functional requirements such as maintainability and transferability defined in ISO 25010:2011 standard^[25]
• business requirements and environmental contexts of a system that may change over time, such as legal, social, financial, competitive, and technology concerns^[26]

The outputs of the analysis activity are those requirements that have a measurable impact on a software system's architecture, called architecturally significant requirements.^[27]

Architectural synthesis or design is the process of creating an architecture. Given the architecturally significant requirements determined by the analysis, the current state of the design and the results of any evaluation activities, the design is created and improved.^{[24][4]:311–326}

Architecture evaluation is the process of determining how well the current design or a portion of it satisfies the requirements derived during analysis. An evaluation can occur whenever an architect is considering a design decision, it can occur after some portion of the design has been completed, it can occur after the final design has been completed or it can occur after the system has been constructed. Some of the available software architecture evaluation techniques include Architecture Tradeoff Analysis Method (ATAM) and TARA.^[28] Frameworks for comparing the techniques are discussed in frameworks such as SARA Report^[16] and Architecture Reviews: Practice and Experience.^[29]

Architecture evolution is the process of maintaining and adapting an existing software architecture to meet changes in requirements and environment. As software architecture provides a fundamental structure of a software system, its evolution and maintenance would necessarily impact its fundamental structure. As such, architecture evolution is concerned with adding new functionality as well as maintaining existing functionality and system behavior.

Architecture requires critical supporting activities. These supporting activities take place throughout the core software architecture process. They include knowledge management and communication, design reasoning and decision making, and documentation.

Architecture supporting activities[edit]

Software architecture supporting activities are carried out during core software architecture activities. These supporting activities assist a software architect to carry out analysis, synthesis, evaluation, and evolution. For instance, an architect has to gather knowledge, make decisions and document during the analysis phase.

• Knowledge management and communication is the act of exploring and managing knowledge that is essential to designing a software architecture. A software architect does not work in isolation. They get inputs, functional and non-functional requirements and design contexts, from various stakeholders; and provides outputs to stakeholders. Software architecture knowledge is often tacit and is retained in the heads of stakeholders. Software architecture knowledge management activity is about finding, communicating, and retaining knowledge. As software architecture design issues are intricate and interdependent, a knowledge gap in design reasoning can lead to incorrect software architecture design.^[23][30] Examples of knowledge management and communication activities include searching for design patterns, prototyping, asking experienced developers and architects, evaluating the designs of similar systems, sharing knowledge with other designers and stakeholders, and documenting experience in a wiki page.
• Design reasoning and decision making is the activity of evaluating design decisions. This activity is fundamental to all three core software architecture activities.^[9][31] It entails gathering and associating decision contexts, formulating design decision problems, finding solution options and evaluating tradeoffs before making decisions. This process occurs at different levels of decision granularity while evaluating significant architectural requirements and software architecture decisions, and software architecture analysis, synthesis, and evaluation. Examples of reasoning activities include understanding the impacts of a requirement or a design on quality attributes, questioning the issues that a design might cause, assessing possible solution options, and evaluating the tradeoffs between solutions.
• Documentation is the act of recording the design generated during the software architecture process. A system design is described using several views that frequently include a static view showing the code structure of the system, a dynamic view showing the actions of the system during execution, and a deployment view showing how a system is placed on hardware for execution. Kruchten's 4+1 view suggests a description of commonly used views for documenting software architecture;^[32] Documenting Software Architectures: Views and Beyond has descriptions of the kinds of notations that could be used within the view description.^[1] Examples of documentation activities are writing a specification, recording a system design model, documenting a design rationale, developing a viewpoint, documenting views.

Software architecture topics[edit]

Software architecture description[edit]

Software architecture description involves the principles and practices of modeling and representing architectures, using mechanisms such as: architecture description languages, architecture viewpoints, and architecture frameworks.

Architecture description languages[edit]

An architecture description language (ADL) is any means of expression used to describe a software architecture (ISO/IEC/IEEE 42010).Many special-purpose ADLs have been developed since the 1990s, including AADL (SAE standard), Wright (developed by Carnegie Mellon), Acme (developed by Carnegie Mellon), xADL (developed by UCI), Darwin (developed by Imperial College London), DAOP-ADL (developed by University of Málaga), SBC-ADL (developed by National Sun Yat-Sen University), and ByADL (University of L'Aquila, Italy).

Architectural Drawing Software Free Downl…

Architecture viewpoints[edit]

Software architecture descriptions are commonly organized into views, which are analogous to the different types of blueprints made in building architecture. Each view addresses a set of system concerns, following the conventions of its viewpoint, where a viewpoint is a specification that describes the notations, modeling, and analysis techniques to use in a view that express the architecture in question from the perspective of a given set of stakeholders and their concerns (ISO/IEC/IEEE 42010). The viewpoint specifies not only the concerns framed (i.e., to be addressed) but the presentation, model kinds used, conventions used and any consistency (correspondence) rules to keep a view consistent with other views.

Architecture frameworks[edit]

An architecture framework captures the 'conventions, principles and practices for the description of architectures established within a specific domain of application and/or community of stakeholders' (ISO/IEC/IEEE 42010). A framework is usually implemented in terms of one or more viewpoints or ADLs.

Architectural styles and patterns[edit]

An architectural pattern is a general, reusable solution to a commonly occurring problem in software architecture within a given context. Architectural patterns are often documented as software design patterns.

Following traditional building architecture, a 'software architectural style' is a specific method of construction, characterized by the features that make it notable' (architectural style).

“

An architectural style defines: a family of systems in terms of a pattern of structural organization; a vocabulary of components and connectors, with constraints on how they can be combined.[33]

”

“

Architectural styles are reusable 'packages' of design decisions and constraints that are applied to an architecture to induce chosen desirable qualities.[34]

”

There are many recognized architectural patterns and styles, among them:

• Client-server (2-tier, 3-tier, n-tier, cloud computing exhibit this style)
• Event-driven (or implicit invocation)
• Layered (or multilayered architecture)
• Peer-to-peer (P2P)
• Representational state transfer (REST)

Some treat architectural patterns and architectural styles as the same,^[35] some treat styles as specializations of patterns. What they have in common is both patterns and styles are idioms for architects to use, they 'provide a common language'^[35] or 'vocabulary'^[33] with which to describe classes of systems.

Software architecture and agile development[edit]

There are also concerns that software architecture leads to too much Big Design Up Front, especially among proponents of agile software development. A number of methods have been developed to balance the trade-offs of up-front design and agility,^[36] including the agile method DSDM which mandates a 'Foundations' phase during which 'just enough' architectural foundations are laid. IEEE Software devoted a special issue^[37] to the interaction between agility and architecture.

Software architecture erosion[edit]

Software architecture erosion (or 'decay') refers to the gap observed between the planned and actual architecture of a software system as realized in its implementation.^[38] Software architecture erosion occurs when implementation decisions either do not fully achieve the architecture-as-planned or otherwise violate constraints or principles of that architecture.^[2] The gap between planned and actual architectures is sometimes understood in terms of the notion of technical debt.

As an example, consider a strictly layered system, where each layer can only use services provided by the layer immediately below it. Any source code component that does not observe this constraint represents an architecture violation. If not corrected, such violations can transform the architecture into a monolithic block, with adverse effects on understandability, maintainability, and evolvability.

Various approaches have been proposed to address erosion. 'These approaches, which include tools, techniques, and processes, are primarily classified into three general categories that attempt to minimize, prevent and repair architecture erosion. Within these broad categories, each approach is further broken down reflecting the high-level strategies adopted to tackle erosion. These are process-oriented architecture conformance, architecture evolution management, architecture design enforcement, architecture to implementation linkage, self-adaptation and architecture restoration techniques consisting of recovery, discovery, and reconciliation.'^[39]

There are two major techniques to detect architectural violations: reflexion models and domain-specific languages. Reflexion model (RM) techniques compare a high-level model provided by the system's architects with the source code implementation. There are also domain-specific languages with a focus on specifying and checking architectural constraints.

Software architecture recovery[edit]

Software architecture recovery (or reconstruction, or reverse engineering) includes the methods, techniques, and processes to uncover a software system's architecture from available information, including its implementation and documentation. Architecture recovery is often necessary to make informed decisions in the face of obsolete or out-of-date documentation and architecture erosion: implementation and maintenance decisions diverging from the envisioned architecture.^[40] Practices exist to recover software architecture as Static program analysis. This is a part of subjects covered by the Software intelligence practice.

Related fields[edit]

Design[edit]

Architecture is design but not all design is architectural.^[1] In practice, the architect is the one who draws the line between software architecture (architectural design) and detailed design (non-architectural design). There are no rules or guidelines that fit all cases, although there have been attempts to formalize the distinction. According to the Intension/Locality Hypothesis,^[41] the distinction between architectural and detailed design is defined by the Locality Criterion,^[41] according to which a statement about software design is non-local (architectural) if and only if a program that satisfies it can be expanded into a program that does not. For example, the client–server style is architectural (strategic) because a program that is built on this principle can be expanded into a program that is not client–server—for example, by adding peer-to-peer nodes.

Requirements engineering[edit]

Requirements engineering and software architecture can be seen as complementary approaches: while software architecture targets the 'solution space' or the 'how', requirements engineering addresses the 'problem space' or the 'what'.^[42] Requirements engineering entails the elicitation, negotiation, specification, validation, documentation and management of requirements. Both requirements engineering and software architecture revolve around stakeholder concerns, needs and wishes.

There is considerable overlap between requirements engineering and software architecture, as evidenced for example by a study into five industrial software architecture methods that concludes that 'the inputs (goals, constraints, etc.) are usually ill-defined, and only get discovered or better understood as the architecture starts to emerge' and that while 'most architectural concerns are expressed as requirements on the system, they can also include mandated design decisions'.^[24] In short, the choice of required behavior given a particular problem impacts the architecture of the solution that addresses that problem, while at the same time the architectural design may impact the problem and introduce new requirements.^[43] Approaches such as the Twin Peaks model^[44] aim to exploit the synergistic relation between requirements and architecture.

Other types of 'architecture'[edit]

Computer architecture

Computer architecture targets the internal structure of a computer system, in terms of collaborating hardware components such as the CPU – or processor – the bus and the memory.

Systems architecture

The term systems architecture has originally been applied to the architecture of systems that consists of both hardware and software. The main concern addressed by the systems architecture is then the integration of software and hardware in a complete, correctly working device. In another common – much broader – meaning, the term applies to the architecture of any complex system which may be of technical, sociotechnical or social nature.

Enterprise architecture

The goal of enterprise architecture is to 'translate business vision and strategy into effective enterprise'.^[45] Enterprise architecture frameworks, such as TOGAF and the Zachman Framework, usually distinguish between different enterprise architecture layers. Although terminology differs from framework to framework, many include at least a distinction between a business layer, an application (or information) layer, and a technology layer. Enterprise architecture addresses among others the alignment between these layers, usually in a top-down approach.

See also[edit]

References[edit]

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2. ^ ^abcdPerry, D. E.; Wolf, A. L. (1992). 'Foundations for the study of software architecture'(PDF). ACM SIGSOFT Software Engineering Notes. 17 (4): 40. CiteSeerX10.1.1.40.5174. doi:10.1145/141874.141884.
3. ^'Software Architecture'. www.sei.cmu.edu. Retrieved 2018-07-23.
4. ^ ^abcdefghijBass, Len; Paul Clements; Rick Kazman (2012). Software Architecture in Practice, Third Edition. Boston: Addison-Wesley. ISBN978-0-321-81573-6.
5. ^SEI (2006). 'How do you define Software Architecture?'. Retrieved 2012-09-12.
6. ^Garlan & Shaw (1994). 'An Introduction to Software Architecture'(PDF). Retrieved 2012-09-13.
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8. ^ISO/IEC/IEEE 42010: Defining 'architecture'. Iso-architecture.org. Retrieved on 2013-07-21.
9. ^ ^abJansen, A.; Bosch, J. (2005). 'Software Architecture as a Set of Architectural Design Decisions'. 5th Working IEEE/IFIP Conference on Software Architecture (WICSA'05). p. 109. CiteSeerX10.1.1.60.8680. doi:10.1109/WICSA.2005.61. ISBN978-0-7695-2548-8.
10. ^Ali Babar, Muhammad; Dingsoyr, Torgeir; Lago, Patricia; van Vliet, Hans (2009). Software Architecture Knowledge Management. Dordrecht Heidelberg London New York: Springer. ISBN978-3-642-02373-6.
11. ^ ^abcGeorge Fairbanks (2010). Just Enough Software Architecture. Marshall & Brainerd.
12. ^ ^abISO/IEC/IEEE (2011). 'ISO/IEC/IEEE 42010:2011 Systems and software engineering – Architecture description'. Retrieved 2012-09-12.
13. ^Muller, Gerrit (August 20, 2007). 'A Reference Architecture Primer'(PDF). Gaudi site. Retrieved November 13, 2015.
14. ^Angelov, Samuil; Grefen, Paul; Greefhorst, Danny (2009). 'A Classification of Software Reference Architectures: Analyzing Their Success and Effectiveness'. Proc. Of WICSA/ECSA 2009: 141–150. CiteSeerX10.1.1.525.7208. doi:10.1109/WICSA.2009.5290800. ISBN978-1-4244-4984-2.
15. ^Brooks, Jr., Frederick P. (1975). The Mythical Man-Month – Essays on Software Engineering. Addison-Wesley. ISBN978-0-201-00650-6.
16. ^ ^abObbink, H.; Kruchten, P.; Kozaczynski, W.; Postema, H.; Ran, A.; Dominick, L.; Kazman, R.; Hilliard, R.; Tracz, W.; Kahane, E. (Feb 6, 2002). 'Software Architecture Review and Assessment (SARA) Report'(PDF). Retrieved November 1, 2015.
17. ^Poort, Eltjo; van Vliet, Hans (September 2012). 'RCDA: Architecting as a risk- and cost management discipline'. Journal of Systems and Software. 85 (9): 1995–2013. doi:10.1016/j.jss.2012.03.071.
18. ^P. Naur; B. Randell, eds. (1969). 'Software Engineering: Report of a conference sponsored by the NATO Science Committee, Garmisch, Germany, 7–11 Oct. 1968'(PDF). Brussels: NATO, Scientific Affairs Division. Retrieved 2012-11-16.
19. ^P. Kruchten; H. Obbink; J. Stafford (2006). 'The past, present and future of software architecture'. IEEE Software. 23 (2): 22. doi:10.1109/MS.2006.59.
20. ^University of Waterloo (2006). 'A Very Brief History of Computer Science'. Retrieved 2006-09-23.
21. ^IEEE Transactions on Software Engineering (2006). 'Introduction to the Special Issue on Software Architecture'. doi:10.1109/TSE.1995.10003.Cite journal requires journal= (help)
22. ^Garlan & Shaw (1994). 'An Introduction to Software Architecture'(PDF). Retrieved 2006-09-25.
23. ^ ^abKruchten, P. (2008). 'What do software architects really do?'. Journal of Systems and Software. 81 (12): 2413–2416. doi:10.1016/j.jss.2008.08.025.
24. ^ ^abcChristine Hofmeister; Philippe Kruchten; Robert L. Nord; Henk Obbink; Alexander Ran; Pierre America (2007). 'A general model of software architecture design derived from five industrial approaches'. Journal of Systems and Software. 80 (1): 106–126. doi:10.1016/j.jss.2006.05.024.
25. ^ ^abISO/IEC (2011). 'ISO/IEC 25010:2011 Systems and software engineering – Systems and software Quality Requirements and Evaluation (SQuaRE) – System and software quality models'. Retrieved 2012-10-08.
26. ^Osterwalder and Pigneur (2004). 'An Ontology for e-Business Models'(PDF): 65–97. CiteSeerX10.1.1.9.6922.Cite journal requires journal= (help)
27. ^Chen, Lianping; Ali Babar, Muhammad; Nuseibeh, Bashar (2013). 'Characterizing Architecturally Significant Requirements'. IEEE Software. 30 (2): 38–45. doi:10.1109/MS.2012.174. hdl:10344/3061.
28. ^Woods, E. (2012). 'Industrial architectural assessment using TARA'. Journal of Systems and Software. 85 (9): 2034–2047. doi:10.1016/j.jss.2012.04.055.
29. ^Maranzano, J. F.; Rozsypal, S. A.; Zimmerman, G. H.; Warnken, G. W.; Wirth, P. E.; Weiss, D. M. (2005). 'Architecture Reviews: Practice and Experience'. IEEE Software. 22 (2): 34. doi:10.1109/MS.2005.28.
30. ^Babar, M.A.; Dingsøyr, T.; Lago, P.; Vliet, H. van (2009). Software Architecture Knowledge Management:Theory and Practice (eds.), First Edition. Springer. ISBN978-3-642-02373-6.
31. ^Tang, A.; Han, J.; Vasa, R. (2009). 'Software Architecture Design Reasoning: A Case for Improved Methodology Support'. IEEE Software. 26 (2): 43. doi:10.1109/MS.2009.46.
32. ^Kruchten, Philippe (1995). 'Architectural Blueprints – The '4+1' View Model of Software Architecture'(PDF). IEEE Software. 12 (6): 42–50. doi:10.1109/52.469759.
33. ^ ^abShaw, Mary; Garlan, David (1996). Software architecture: perspectives on an emerging discipline. Prentice Hall. ISBN978-0-13-182957-2.
34. ^UCI Software Architecture Research – UCI Software Architecture Research: Architectural Styles. Isr.uci.edu. Retrieved on 2013-07-21.
35. ^ ^abChapter 3: Architectural Patterns and Styles. Msdn.microsoft.com. Retrieved on 2013-07-21.
36. ^Boehm, Barry; Turner, Richard (2004). Balancing Agility and Discipline. Addison-Wesley. ISBN978-0-321-18612-6.
37. ^'IEEE Software Special Issue on Agility and Architecture'. April 2010. Retrieved 14 September 2012.
38. ^Terra, R., M.T. Valente, K. Czarnecki, and R.S. Bigonha, 'Recommending Refactorings to Reverse Software Architecture Erosion',16th European Conference on Software Maintenance and Reengineering, 2012. http://gsd.uwaterloo.ca/sites/default/files/Full%20Text.pdf
39. ^de Silva, L.; Balasubramaniam, D. (2012). 'Controlling software architecture erosion: A survey'. Journal of Systems and Software. 85 (1): 132–151. doi:10.1016/j.jss.2011.07.036.
40. ^Lungu, M. 'Software architecture recovery', University of Lugano, 2008. http://www.slideshare.net/mircea.lungu/software-architecture-recovery-in-five-questions-presentation
41. ^ ^abAmnon H. Eden; Rick Kazman (2003). 'Architecture Design Implementation'(PDF). Archived from the original(PDF) on 2007-09-28.
42. ^C. Shekaran; D. Garlan; M. Jackson; N.R. Mead; C. Potts; H.B. Reubenstein (1994). 'The role of software architecture in requirements engineering'. Proceedings of IEEE International Conference on Requirements Engineering: 239–245. doi:10.1109/ICRE.1994.292379. ISBN978-0-8186-5480-0.
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45. ^Definition of Enterprise Architecture, Gartner

Further reading[edit]

• Paul Clements, Felix Bachmann, Len Bass, David Garlan, James Ivers, Reed Little, Paulo Merson, Robert Nord, Judith Stafford: Documenting Software Architectures: Views and Beyond, Second Edition. Addison-Wesley, 2010, ISBN0-321-55268-7.

This book describes what software architecture is and shows how to document it in multiple views, using UML and other notations. It also explains how to complement the architecture views with behavior, software interface, and rationale documentation. Accompanying the book is a wiki that contains an example of software architecture documentation.

• Len Bass, Paul Clements, Rick Kazman: Software Architecture in Practice, Third Edition. Addison Wesley, 2012, ISBN0-321-81573-4 (This book, now in its third edition, eloquently covers the fundamental concepts of the discipline. The theme is centered on achieving quality attributes of a system.)
• Amnon H. Eden, Rick Kazman. Architecture, Design, Implementation. On the distinction between architectural design and detailed design.
• Garzás, Javier; Piattini, Mario (2005). 'An ontology for micro-architectural design knowledge'. IEEE Software. 22 (2): 28–33. doi:10.1109/MS.2005.26.
• Kruchten, Philippe (1995). 'Architectural Blueprints – The '4+1' View Model of Software Architecture'(PDF). IEEE Software. 12 (6): 42–50. doi:10.1109/52.469759.
• Shan, Tony; Hua, Winnie (October 2006). 'Solution Architecting Mechanism'. Proceedings of the 10th IEEE International EDOC Enterprise Computing Conference: 23–32. doi:10.1109/EDOC.2006.54. ISBN978-0-7695-2558-7.
• Martin Fowler (with Ralph Johnson) Who Needs an Architect? IEEE Software, Jul/Aug 2003
• Bell, Michael (2008). Service-Oriented Modeling: Service Analysis, Design, and Architecture. Wiley. ASIN0470141115.CS1 maint: ASIN uses ISBN (link)

External links[edit]

Wikimedia Commons has media related to Software architecture.

Wikiquote has quotations related to: Software architecture

• Collection of software architecture definitions at Software Engineering Institute (SEI), Carnegie Mellon University (CMU)
• International Association of IT Architects (IASA Global), formerly known as the International Association for Software Architects (IASA)
• SoftwareArchitecturePortal.org – website of IFIP Working Group 2.10 on Software Architecture
• SoftwareArchitectures.com – independent resource of information on the discipline
• Software Architecture, chapter 1 of Roy Fielding's REST dissertation
• The Spiral Architecture Driven Development – the SDLC based on the Spiral model aims to reduce the risks of ineffective architecture

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