Software architecture is the fundamental structure 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.
The ''architecture'' of a software system is a metaphor, analogous to the
architecture
Architecture is the art and technique of designing and building, as distinguished from the skills associated with construction. It is both the process and the product of sketching, conceiving, planning, designing, and constructing building ...
of a building.
It functions as a blueprint for the system and the developing project, which
project management
Project management is the process of leading the work of a team to achieve all project goals within the given constraints. This information is usually described in project documentation, created at the beginning of the development process. Th ...
can later use to extrapolate the tasks necessary to be executed by the teams and people involved.
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 the software.
For example, the systems that controlled the
Space Shuttle
The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program na ...
launch vehicle had the requirement of being very fast and very reliable. Therefore, an appropriate
real-time computing
Real-time computing (RTC) is the computer science term for hardware and software systems subject to a "real-time constraint", for example from event to system response. Real-time programs must guarantee response within specified time constrai ...
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.
Scope
Opinions vary as to the scope of software architectures:
* Macroscopic system structure: this refers to architecture as a higher-level
abstraction
Abstraction in its main sense is a conceptual process wherein general rules and concepts are derived from the usage and classification of specific examples, literal ("real" or "concrete") signifiers, first principles, or other methods.
"An abstr ...
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: 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
* Things that people perceive as hard to change: 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: 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
Knowledge management (KM) is the collection of methods relating to creating, sharing, using and managing the knowledge and information of an organization. It refers to a multidisciplinary approach to achieve organisational objectives by making ...
.
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.
Characteristics
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 that they are addressed is part of designing the system.
This implies that architecture involves dealing with a broad variety of concerns and stakeholders, and has a multidisciplinary nature.
Separation of concerns
In computer science, separation of concerns is a design principle for separating a computer program into distinct sections. Each section addresses a separate '' concern'', a set of information that affects the code of a computer program. A concern ...
: 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.
These separate descriptions are called architectural views (see for example the
4+1 architectural view model).
Quality-driven: classic
software design
Software design is the process by which an agent creates a specification of a software artifact intended to accomplish goals, using a set of primitive components and subject to constraints. Software design may refer to either "all the activity ...
approaches (e.g.
Jackson Structured Programming) were driven by required functionality and the flow of data through the system, but the current insight
is that the architecture of a software system is more closely related to its
quality attributes
In systems engineering and requirements engineering, a non-functional requirement (NFR) is a requirement that specifies criteria that can be used to judge the operation of a system, rather than specific behaviours. They are contrasted with func ...
such as
fault-tolerance
Fault tolerance is the property that enables a system to continue operating properly in the event of the failure of one or more faults within some of its components. If its operating quality decreases at all, the decrease is proportional to the ...
,
backward compatibility
Backward compatibility (sometimes known as backwards compatibility) is a property of an operating system, product, or technology that allows for interoperability with an older legacy system, or with input designed for such a system, especiall ...
,
extensibility,
reliability
Reliability, reliable, or unreliable may refer to:
Science, technology, and mathematics Computing
* Data reliability (disambiguation), a property of some disk arrays in computer storage
* High availability
* Reliability (computer networking), a ...
,
maintainability
In engineering, maintainability is the ease with which a product can be maintained to:
* correct defects or their cause,
* Repair or replace faulty or worn-out components without having to replace still working parts,
* prevent unexpected working ...
,
availability
In reliability engineering, the term availability has the following meanings:
* The degree to which a system, subsystem or equipment is in a specified operable and committable state at the start of a mission, when the mission is called for at ...
, security, usability, and other such –
ilities
In systems engineering and requirements engineering, a non-functional requirement (NFR) is a requirement that specifies criteria that can be used to judge the operation of a system, rather than specific behaviours. They are contrasted with func ...
. Stakeholder concerns often translate into
requirements on these quality attributes, which are variously called
non-functional requirements
In systems engineering and requirements engineering, a non-functional requirement (NFR) is a requirement that specifies criteria that can be used to judge the operation of a system, rather than specific behaviours. They are contrasted with func ...
, 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,
tactic,
reference architecture A reference architecture in the field of software architecture or enterprise architecture provides a template solution for an architecture for a particular domain. It also provides a common vocabulary with which to discuss implementations, often wi ...
and
architectural pattern.
Conceptual integrity: a term introduced by
Fred Brooks
Frederick Phillips Brooks Jr. (April 19, 1931 – November 17, 2022) was an American computer architect, software engineer, and computer scientist, best known for managing the development of IBM's System/360 family of computers and the O ...
in his 1975 book ''
The Mythical Man-Month
''The Mythical Man-Month: Essays on Software Engineering'' is a book on software engineering and project management by Fred Brooks first published in 1975, with subsequent editions in 1982 and 1995. Its central theme is that adding manpower to a ...
'' 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.
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
Software architecture is an "intellectually graspable" abstraction of a complex system.
This abstraction provides a number of benefits:
* ''It gives a basis for analysis of software systems' behavior before the system has been built.''
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.
A number of techniques have been developed to perform such analyses, such as
ATAM In software engineering, architecture tradeoff analysis method (ATAM) is a risk-mitigation process used early in the software development life cycle.
ATAM was developed by the Software Engineering Institute at the Carnegie Mellon University. Its pu ...
or by creating a visual representation of the software system.
* ''It provides a basis for re-use of elements and decisions.''
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.''
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.''
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.
* ''It enables
cost reduction.'' Software architecture is a means to manage risk and costs in complex IT projects.
History
The comparison between software design and (civil) architecture was first drawn in the late 1960s, but the term "software architecture" did not see widespread usage until the 1990s. The field of
computer science
Computer science is the study of computation, automation, and information. Computer science spans theoretical disciplines (such as algorithms, theory of computation, information theory, and automation) to Applied science, practical discipli ...
had encountered problems associated with complexity since its formation. Earlier problems of complexity were solved by developers by choosing the right
data structure
In computer science, a data structure is a data organization, management, and storage format that is usually chosen for efficient access to data. More precisely, a data structure is a collection of data values, the relationships among them, a ...
s, developing
algorithm
In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific Computational problem, problems or to perform a computation. Algorithms are used as specificat ...
s, and by applying the concept of
separation of concerns
In computer science, separation of concerns is a design principle for separating a computer program into distinct sections. Each section addresses a separate '' concern'', a set of information that affects the code of a computer program. A concern ...
. Although the term "software architecture" is relatively new to the industry, the fundamental principles of the field have been applied sporadically by
software engineering
Software engineering is a systematic engineering approach to software development.
A software engineer is a person who applies the principles of software engineering to design, develop, maintain, test, and evaluate computer software. The term '' ...
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
diagram
A diagram is a symbolic representation of information using visualization techniques. Diagrams have been used since prehistoric times on walls of caves, but became more prevalent during the Enlightenment. Sometimes, the technique uses a three- ...
s.
Software architecture as a concept has its origins in the research of
Edsger Dijkstra
Edsger Wybe Dijkstra ( ; ; 11 May 1930 – 6 August 2002) was a Dutch computer scientist, programmer, software engineer, systems scientist, and science essayist. He received the 1972 Turing Award for fundamental contributions to developing progra ...
in 1968 and
David Parnas
David Lorge Parnas (born February 10, 1941) is a Canadian early pioneer of software engineering, who developed the concept of information hiding in modular programming, which is an important element of object-oriented programming today. He is al ...
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
A pattern is a regularity in the world, in human-made design, or in abstract ideas. As such, the elements of a pattern repeat in a predictable manner. A geometric pattern is a kind of pattern formed of geometric shapes and typically repeated li ...
),
architecture description language
Architecture description languages (ADLs) are used in several disciplines: system engineering, software engineering, and enterprise modelling and engineering.
The system engineering community uses an architecture description language as a langua ...
s,
architecture documentation, and
formal method
In computer science, formal methods are mathematically rigorous techniques for the specification, development, and verification of software and hardware systems. The use of formal methods for software and hardware design is motivated by the exp ...
s.
Research institutions have played a prominent role in furthering software architecture as a discipline.
Mary Shaw and David Garlan of
Carnegie Mellon
Carnegie may refer to:
People
* Carnegie (surname), including a list of people with the name
* Clan Carnegie, a lowland Scottish clan
Institutions Named for Andrew Carnegie
*Carnegie Building (Troy, New York), on the campus of Rensselaer Polyt ...
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
The University of California, Irvine (UCI or UC Irvine) is a public land-grant research university in Irvine, California. One of the ten campuses of the University of California system, UCI offers 87 undergraduate degrees and 129 graduate and pr ...
'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
IEEE 1471 is a superseded IEEE standard for describing the architecture of a "software-intensive system", also known as software architecture.
In 2011 it was superseded by ISO/IEC/IEEE 42010, ''Systems and software engineering — Architecture de ...
-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).
While in
IEEE 1471
IEEE 1471 is a superseded IEEE standard for describing the architecture of a "software-intensive system", also known as software architecture.
In 2011 it was superseded by ISO/IEC/IEEE 42010, ''Systems and software engineering — Architecture de ...
, 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
The ISO/IEC 15288 is a technical standard in systems engineering which covers processes and lifecycle stages, developed by the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC). Planning ...
and
ISO/IEC 12207
ISO/IEC/IEEE 12207 ''Systems and software engineering – Software life cycle processes'' is an international standard for software lifecycle processes. First introduced in 1995, it aims to be a primary standard that defines all the processes requ ...
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 Solution architecture, term used in information technology with various definitions such as; "A description of a discrete and focused business operation or activity and how IS/ IT supports that operation".
Definitions
The Open Group's definition ...
.
Architecture activities
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.
There are four core activities in software architecture design.
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 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
ISO/IEC 9126 ''Software engineering — Product quality'' was an international standard for the evaluation of software quality. It has been replaced by ISO/IEC 25010:2011.
The fundamental objective of the ISO/IEC 9126 standard is to address ...
:2011 standard
* development-time of non-functional requirements such as maintainability and transferability defined in ISO 25010:2011 standard
* business requirements and environmental contexts of a system that may change over time, such as legal, social, financial, competitive, and technology concerns
The outputs of the analysis activity are those requirements that have a measurable impact on a software system's architecture, called architecturally significant requirements.
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.
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.
Frameworks for comparing the techniques are discussed in frameworks such as ''SARA Report''
and ''Architecture Reviews: Practice and Experience''.
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
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.
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.
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.
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;
''Documenting Software Architectures: Views and Beyond'' has descriptions of the kinds of notations that could be used within the view description.
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
Software architecture description
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
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
Wright is an occupational surname originating in England. The term 'Wright' comes from the circa 700 AD Old English word 'wryhta' or 'wyrhta', meaning worker or shaper of wood. Later it became any occupational worker (for example, a shipwright i ...
(developed by Carnegie Mellon),
Acme (developed by Carnegie Mellon), xADL (developed by UCI),
Darwin (developed by
Imperial College London
Imperial College London (legally Imperial College of Science, Technology and Medicine) is a public research university in London, United Kingdom. Its history began with Prince Albert, consort of Queen Victoria, who developed his vision for a cu ...
), DAOP-ADL (developed by University of Málaga), SBC-ADL (developed by
National Sun Yat-Sen University
National Sun Yat-sen University (NSYSU; ) is a public research-intensive university renowned as an official think tank scholars' community, located in Sizihwan, Kaohsiung, Taiwan. NSYSU is listed as one of six national research universities, ...
), and
ByADL (University of L'Aquila, Italy).
Architecture viewpoints
![4+1 Architectural View Model](https://upload.wikimedia.org/wikipedia/commons/e/e6/4%2B1_Architectural_View_Model.svg)
Software architecture descriptions are commonly organized into
views
A view is a sight or prospect or the ability to see or be seen from a particular place.
View, views or Views may also refer to:
Common meanings
* View (Buddhism), a charged interpretation of experience which intensely shapes and affects thou ...
, which are analogous to the different types of
blueprint
A blueprint is a reproduction of a technical drawing or engineering drawing using a contact print process on light-sensitive sheets. Introduced by Sir John Herschel in 1842, the process allowed rapid and accurate production of an unlimited number ...
s made in building
architecture
Architecture is the art and technique of designing and building, as distinguished from the skills associated with construction. It is both the process and the product of sketching, conceiving, planning, designing, and constructing building ...
. 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 expresses 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
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
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 is a set of characteristics and features that make a building or other structure notable or historically identifiable. It is a sub-class of style in the visual arts generally, and most styles in architecture relate closely ...
).
There are many recognized architectural patterns and styles, among them:
*
Blackboard
*
Client-server (2-tier,
3-tier
In software engineering, multitier architecture (often referred to as ''n''-tier architecture) is a client–server architecture in which presentation, application processing and data management functions are physically separated. The most wides ...
,
''n''-tier,
cloud computing
Cloud computing is the on-demand availability of computer system resources, especially data storage ( cloud storage) and computing power, without direct active management by the user. Large clouds often have functions distributed over mul ...
exhibit this style)
*
Component-based
Component-based software engineering (CBSE), also called component-based development (CBD), is a branch of software engineering that emphasizes the separation of concerns with respect to the wide-ranging functionality available throughout a give ...
*
Data-centric
*
Event-driven
Event driven may refer to:
The term event-driven refers to a methodology that focuses on events and event dependencies.
Examples include
* Event-driven finite-state machine, finite-state machine where the transition from one state to another ...
(or
implicit invocation
Implicit invocation is a term used by some authors for a style of software architecture in which a system is structured around event handling, using a form of callback. It is closely related to inversion of control and what is known informally a ...
)
*
Layered (or
multilayered architecture
In software engineering, multitier architecture (often referred to as ''n''-tier architecture) is a client–server architecture in which presentation, application processing and data management functions are physically separated. The most wide ...
)
*
Microservices architecture
*
Monolithic application
In software engineering, a monolithic application describes a single-tiered software application in which the user interface and data access code are combined into a single program from a single platform.
A monolithic application is self-contained ...
*
Peer-to-peer
Peer-to-peer (P2P) computing or networking is a distributed application architecture that partitions tasks or workloads between peers. Peers are equally privileged, equipotent participants in the network. They are said to form a peer-to-peer n ...
(P2P)
*
Pipes and filters
Pipe(s), PIPE(S) or piping may refer to:
Objects
* Pipe (fluid conveyance), a hollow cylinder following certain dimension rules
** Piping, the use of pipes in industry
* Smoking pipe
** Tobacco pipe
* Half-pipe and quarter pipe, semi-circula ...
*
Plug-ins
*
Reactive architecture
Reactive may refer to:
*Generally, capable of having a reaction (disambiguation)
*An adjective abbreviation denoting a Bowling ball#Coverstock technology, bowling ball coverstock made of reactive resin
*Reactivity (chemistry)
*Reactive mind
*React ...
*
Representational state transfer (REST)
*
Rule-based
*
Service-oriented
*
Shared nothing architecture
Shared may refer to:
* Sharing
* Shared ancestry or Common descent
* Shared care
* Shared-cost service
* Shared decision-making in medicine
* Shared delusion, various meanings
* Shared government
* Shared intelligence or collective intelligence
...
*
Space-based architecture
A Space-based architecture (SBA) is an approach to distributed computing systems where the various components interact with each other by ''exchanging'' tuples or entries via one or more shared spaces. This is contrasted with the more common Mess ...
Some treat architectural patterns and architectural styles as the same,
[Chapter 3: Architectural Patterns and Styles]
Msdn.microsoft.com. Retrieved on 2013-07-21. 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"
[ or "vocabulary"][ with which to describe classes of systems.
]
Software architecture and agile development
There are also concerns that software architecture leads to too much Big Design Up Front
Big Design Up Front (BDUF) is a software development approach in which the program's design is to be completed and perfected before that program's implementation is started. It is often associated with the waterfall model of software development.
...
, 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, including the agile method DSDM which mandates a "Foundations" phase during which "just enough" architectural foundations are laid. ''IEEE Software
''IEEE Software'' is a bimonthly peer-reviewed magazine and scientific journal published by the IEEE Computer Society covering all aspects of software engineering, processes, and practices. Its mission is to be the best source of reliable, use ...
'' devoted a special issue to the interaction between agility and architecture.
Software architecture erosion
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. 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.
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."
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 language
A domain-specific language (DSL) is a computer language specialized to a particular application domain. This is in contrast to a general-purpose language (GPL), which is broadly applicable across domains. There are a wide variety of DSLs, ranging f ...
s with a focus on specifying and checking architectural constraints.
Software architecture recovery
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.[
Lungu, M. "Software architecture recovery", University of Lugano, 2008.
http://www.slideshare.net/mircea.lungu/software-architecture-recovery-in-five-questions-presentation
] Practices exist to recover software architecture as static program analysis
In computer science, static program analysis (or static analysis) is the analysis of computer programs performed without executing them, in contrast with dynamic program analysis, which is performed on programs during their execution.
The term ...
. This is a part of subjects covered by the software intelligence Software Intelligence is insight into the structural condition of software assets produced by software designed to analyze database structure, software framework and source code to better understand and control complex software systems in Informatio ...
practice.
Related fields
Design
Architecture is design
A design is a plan or specification for the construction of an object or system or for the implementation of an activity or process or the result of that plan or specification in the form of a prototype, product, or process. The verb ''to design'' ...
but not all design is architectural. 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'', the distinction between architectural and detailed design is defined by the ''Locality Criterion'', 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
Peer-to-peer (P2P) computing or networking is a distributed application architecture that partitions tasks or workloads between peers. Peers are equally privileged, equipotent participants in the network. They are said to form a peer-to-peer n ...
nodes.
Requirements engineering
Requirements engineering
Requirements engineering (RE) is the process of defining, documenting, and maintaining requirements in the engineering design process. It is a common role in systems engineering and software engineering.
The first use of the term ''requiremen ...
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
Problem solving is the process of achieving a goal by overcoming obstacles, a frequent part of most activities. Problems in need of solutions range from simple personal tasks (e.g. how to turn on an appliance) to complex issues in business an ...
' or the 'what'. Requirements engineering entails the elicitation, negotiation
Negotiation is a dialogue between two or more people or parties to reach the desired outcome regarding one or more issues of conflict. It is an interaction between entities who aspire to agree on matters of mutual interest. The agreement c ...
, specification
A specification often refers to a set of documented requirements to be satisfied by a material, design, product, or service. A specification is often a type of technical standard.
There are different types of technical or engineering specificati ...
, validation, documentation and management
Management (or managing) is the administration of an organization, whether it is a business, a nonprofit organization, or a government body. It is the art and science of managing resources of the business.
Management includes the activities o ...
of requirement
In product development and process optimization, a requirement is a singular documented physical or functional need that a particular design, product or process aims to satisfy. It is commonly used in a formal sense in engineering design, includ ...
s. 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"''. In short, required behavior impacts solution architecture, which in turn may introduce new requirements. Approaches such as the Twin Peaks model aim to exploit the synergistic relation between requirements and architecture.
Other types of 'architecture'
;Computer architecture
:Computer architecture
In computer engineering, computer architecture is a description of the structure of a computer system made from component parts. It can sometimes be a high-level description that ignores details of the implementation. At a more detailed level, t ...
targets the internal structure of a computer system, in terms of collaborating hardware components such as the CPU – or processor – the bus
A bus (contracted from omnibus, with variants multibus, motorbus, autobus, etc.) is a road vehicle that carries significantly more passengers than an average car or van. It is most commonly used in public transport, but is also in use for cha ...
and the memory
Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered, ...
.
;Systems architecture
:The term systems architecture A system architecture is the conceptual model that defines the structure, behavior, and more views of a system. An architecture description is a formal description and representation of a system, organized in a way that supports reasoning about the ...
has originally been applied to the architecture of system
A system is a group of Interaction, interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its environment (systems), environment, is described by its boundaries, ...
s that consists of both hardware and software
Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work.
At the lowest programming level, executable code consists ...
. 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". Enterprise architecture frameworks
A framework is a generic term commonly referring to an essential supporting structure which other things are built on top of.
Framework may refer to:
Computing
* Application framework, used to implement the structure of an application for an op ...
, such as TOGAF
The Open Group Architecture Framework (TOGAF) is the most used framework for enterprise architecture as of 2020 that provides an approach for designing, planning, implementing, and governing an enterprise information technology architecture. TOG ...
and the Zachman Framework
The Zachman Framework is an enterprise ontology and is a fundamental structure for enterprise architecture which provides a formal and structured way of viewing and defining an enterprise. The ontology is a two dimensional classification sche ...
, usually distinguish between different enterprise architecture layers. Although terminology differs from framework to framework, many include at least a distinction between a ''business
Business is the practice of making one's living or making money by producing or Trade, buying and selling Product (business), products (such as goods and Service (economics), services). It is also "any activity or enterprise entered into for pr ...
layer'', an '' application'' (or ''information
Information is an abstract concept that refers to that which has the power to inform. At the most fundamental level information pertains to the interpretation of that which may be sensed. Any natural process that is not completely random ...
'') ''layer'', and a ''technology
Technology is the application of knowledge to reach practical goals in a specifiable and reproducible way. The word ''technology'' may also mean the product of such an endeavor. The use of technology is widely prevalent in medicine, science, ...
layer''. Enterprise architecture addresses among others the alignment between these layers, usually in a top-down approach.
See also
References
Further reading
*
* - This book covers the fundamental concepts of the discipline. The theme is centered on achieving quality attributes of a system.
* - 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
wiki that contains an example of software architecture documentation
*
*
*
*
* - On the distinction between architectural design and detailed design.
*
*
External links
Explanation on IBM Developerworks
* Collection o
software architecture definitions
at Software Engineering Institute
The Software Engineering Institute (SEI) is an American research and development center headquartered in Pittsburgh, Pennsylvania. Its activities cover cybersecurity, software assurance, software engineering and acquisition, and component capabi ...
(SEI), Carnegie Mellon University
Carnegie Mellon University (CMU) is a private research university in Pittsburgh, Pennsylvania. One of its predecessors was established in 1900 by Andrew Carnegie as the Carnegie Technical Schools; it became the Carnegie Institute of Technology ...
(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
– an independent resource of information on the discipline
chapter 1 of Roy Fielding
Roy Thomas Fielding (born 1965) is an American computer scientist, one of the principal authors of the HTTP specification and the originator of the Representational State Transfer (REST) architectural style. He is an authority on computer network ...
's REST dissertation
When Good Architecture Goes Bad
The Spiral Architecture Driven Development
– the SDLC based on the Spiral model
The spiral model is a risk-driven software development process model. Based on the unique risk patterns of a given project, the spiral model guides a team to adopt elements of one or more process models, such as incremental, waterfall, or evolu ...
aims to reduce the risks of ineffective architecture
Software Architecture Real Life Case Studies
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