Software design
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Software design is the process by which an
agent Agent may refer to: Espionage, investigation, and law *, spies or intelligence officers * Law of agency, laws involving a person authorized to act on behalf of another ** Agent of record, a person with a contractual agreement with an insuranc ...
creates a specification of a
software artifact An artifact is one of many kinds of ''tangible'' by-products produced during the development of software. Some artifacts (e.g., use cases, class diagrams, and other Unified Modeling Language (UML) models, requirements and design documents) help de ...
intended to accomplish
goal A goal is an idea of the future or desired result that a person or a group of people envision, plan and commit to achieve. People endeavour to reach goals within a finite time by setting deadlines. A goal is roughly similar to a purpose or ai ...
s, using a set of primitive components and subject to constraints. Software design may refer to either "all the activity involved in conceptualizing, framing, implementing, commissioning, and ultimately modifying complex systems" or "the activity following requirements specification and before programming, as ... na stylized software engineering process." Software design usually involves problem-solving and planning a
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 ...
solution. This includes both a low-level component and
algorithm design In mathematics and computer science, an algorithm () is a finite sequence of rigorous instructions, typically used to solve a class of specific problems or to perform a computation. Algorithms are used as specifications for performing c ...
and a high-level,
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 ...
design.


Overview

Software design is the process of envisioning and defining software solutions to one or more sets of problems. One of the main components of software design is the software requirements analysis (SRA). SRA is a part of the
software development process In software engineering, a software development process is a process of dividing software development work into smaller, parallel, or sequential steps or sub-processes to improve design, product management. It is also known as a software devel ...
that lists
specifications 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 ...
used in
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 '' ...
. If the software is "semi-automated" or user centered, software design may involve
user experience design User experience design (UX design, UXD, UED, or XD) is the process of defining the experience a user would go through when interacting with a digital product or website. Design decisions in UX design are often driven by research, data analysis, an ...
yielding a storyboard to help determine those specifications. If the software is completely
automated Automation describes a wide range of technologies that reduce human intervention in processes, namely by predetermining decision criteria, subprocess relationships, and related actions, as well as embodying those predeterminations in machines ...
(meaning no user or
user interface In the industrial design field of human–computer interaction, a user interface (UI) is the space where interactions between humans and machines occur. The goal of this interaction is to allow effective operation and control of the machine f ...
), a software design may be as simple as a
flow chart A flowchart is a type of diagram that represents a workflow or process. A flowchart can also be defined as a diagrammatic representation of an algorithm, a step-by-step approach to solving a task. The flowchart shows the steps as boxes of v ...
or text describing a planned sequence of events. There are also semi-standard methods like
Unified Modeling Language The Unified Modeling Language (UML) is a general-purpose, developmental modeling language in the field of software engineering that is intended to provide a standard way to visualize the design of a system. The creation of UML was originally m ...
and Fundamental modeling concepts. In either case, some documentation of the plan is usually the product of the design. Furthermore, a software design may be
platform-independent In computing, cross-platform software (also called multi-platform software, platform-agnostic software, or platform-independent software) is computer software that is designed to work in several computing platforms. Some cross-platform software ...
or platform-specific, depending upon the availability of the technology used for the design. The main difference between software analysis and design is that the output of a software analysis consists of smaller problems to solve. Additionally, the analysis should not be designed very differently across different team members or groups. In contrast, the design focuses on capabilities, and thus multiple designs for the same problem can and will exist. Depending on the environment, the design often varies, whether it is created from reliable
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 ...
or implemented with suitable design patterns. Design examples include operation systems, webpages, mobile devices or even the new cloud computing paradigm. Software design is both a process and a model. The design process is a sequence of steps that enables the designer to describe all aspects of the software for building. Creative skill, past experience, a sense of what makes "good" software, and an overall commitment to quality are examples of critical success factors for a competent design. It is important to note, however, that the design process is not always a straightforward procedure; the design model can be compared to an architect's plans for a house. It begins by representing the totality of the thing that is to be built (e.g., a three-dimensional rendering of the house); slowly, the thing is refined to provide guidance for constructing each detail (e.g., the plumbing lay). Similarly, the design model that is created for software provides a variety of different views of the computer software. Basic design principles enable the software engineer to navigate the design process. Davis suggests a set of principles for software design, which have been adapted and extended in the following list: * The design process should not suffer from "tunnel vision." A good designer should consider alternative approaches, judging each based on the requirements of the problem, the resources available to do the job. * The design should be traceable to the analysis model. Because a single element of the design model can often be traced back to multiple requirements, it is necessary to have a means for tracking how requirements have been satisfied by the design model. * The design should not reinvent the wheel. Systems are constructed using a set of design patterns, many of which have likely been encountered before. These patterns should always be chosen as an alternative to reinvention. Time is short and resources are limited; design time should be invested in representing (truly new) ideas by integrating patterns that already exist (when applicable). * The design should "minimize the intellectual distance" between the software and the problem as it exists in the real world. That is, the structure of the software design should, whenever possible, mimic the structure of the problem domain. * The design should exhibit uniformity and integration. A design is uniform if it appears fully coherent. In order to achieve this outcome, rules of style and format should be defined for a design team before design work begins. A design is integrated if care is taken in defining interfaces between design components. * The design should be structured to accommodate change. The design concepts discussed in the next section enable a design to achieve this principle. * The design should be structured to degrade gently, even when aberrant data, events, or operating conditions are encountered. Well-designed software should never "bomb"; it should be designed to accommodate unusual circumstances, and if it must terminate processing, it should do so in a graceful manner. * Design is not coding, coding is not design. Even when detailed procedural designs are created for program components, the level of abstraction of the design model is higher than the source code. The only design decisions made at the coding level should address the small implementation details that enable the procedural design to be coded. * The design should be assessed for quality as it is being created, not after the fact. A variety of design concepts and design measures are available to assist the designer in assessing quality throughout the development process. * The design should be reviewed to minimize conceptual (semantic) errors. There is sometimes a tendency to focus on minutiae when the design is reviewed, missing the forest for the trees. A design team should ensure that major conceptual elements of the design (omissions, ambiguity, inconsistency) have been addressed before worrying about the syntax of the design model.


Design concepts

The design concepts provide the software designer with a foundation from which more sophisticated methods can be applied. A set of fundamental design concepts has evolved. They are as follows: #
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 ...
- Abstraction is the process or result of generalization by reducing the information content of a concept or an observable phenomenon, typically in order to retain only information which is relevant for a particular purpose. It is an act of Representing essential features without including the background details or explanations. #
Refinement Refinement may refer to: Mathematics * Equilibrium refinement, the identification of actualized equilibria in game theory * Refinement of an equivalence relation, in mathematics ** Refinement (topology), the refinement of an open cover in mathem ...
- It is the process of elaboration. A hierarchy is developed by decomposing a macroscopic statement of function in a step-wise fashion until programming language statements are reached. In each step, one or several instructions of a given program are decomposed into more detailed instructions. Abstraction and Refinement are complementary concepts. # Modularity - Software architecture is divided into components called modules. #
Software Architecture 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. ...
- It refers to the overall structure of the software and the ways in which that structure provides conceptual integrity for a system. Good software architecture will yield a good return on investment with respect to the desired outcome of the project, e.g. in terms of performance, quality, schedule and cost. # Control Hierarchy - A program structure that represents the organization of a program component and implies a hierarchy of control. # Structural Partitioning - The program structure can be divided into both horizontally and vertically. Horizontal partitions define separate branches of modular hierarchy for each major program function. Vertical partitioning suggests that control and work should be distributed top down in the program structure. #
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 ...
- It is a representation of the logical relationship among individual elements of data. # Software Procedure - It focuses on the processing of each module individually. #
Information Hiding In computer science, information hiding is the principle of segregation of the ''design decisions'' in a computer program that are most likely to change, thus protecting other parts of the program from extensive modification if the design decisio ...
- Modules should be specified and designed so that information contained within a module is inaccessible to other modules that have no need for such information. In his object model,
Grady Booch Grady Booch (born February 27, 1955) is an American software engineer, best known for developing the Unified Modeling Language (UML) with Ivar Jacobson and James Rumbaugh. He is recognized internationally for his innovative work in software archi ...
mentions Abstraction, Encapsulation, Modularisation, and Hierarchy as fundamental software design principles. The acronym PHAME (Principles of Hierarchy, Abstraction, Modularisation, and Encapsulation) is sometimes used to refer to these four fundamental principles.


Design considerations

There are many aspects to consider in the design of a piece of software. The importance of each consideration should reflect the goals and expectations that the software is being created to meet. Some of these aspects are: * Compatibility - The software is able to operate with other products that are designed for interoperability with another product. For example, a piece of software may be backward-compatible with an older version of itself. * Extensibility - New capabilities can be added to the software without major changes to the underlying architecture. * Modularity - the resulting software comprises well defined, independent components which leads to better maintainability. The components could be then implemented and tested in isolation before being integrated to form a desired software system. This allows division of work in a software development project. *
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 ...
- The software is resistant to and able to recover from component failure. *
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 ...
- A measure of how easily bug fixes or functional modifications can be accomplished. High maintainability can be the product of modularity and extensibility. * Reliability ( Software durability) - The software is able to perform a required function under stated conditions for a specified period of time. *
Reusability In computer science and software engineering, reusability is the use of existing ''assets'' in some form within the software product development process; these ''assets'' are products and by-products of the software development life cycle and in ...
- The ability to use some or all of the aspects of the preexisting software in other projects with little to no modification. *
Robustness Robustness is the property of being strong and healthy in constitution. When it is transposed into a system, it refers to the ability of tolerating perturbations that might affect the system’s functional body. In the same line ''robustness'' ca ...
- The software is able to operate under stress or tolerate unpredictable or invalid input. For example, it can be designed with resilience to low memory conditions. *
Security Security is protection from, or resilience against, potential harm (or other unwanted coercive change) caused by others, by restraining the freedom of others to act. Beneficiaries (technically referents) of security may be of persons and social ...
- The software is able to withstand and resist hostile acts and influences. * Usability - The software
user interface In the industrial design field of human–computer interaction, a user interface (UI) is the space where interactions between humans and machines occur. The goal of this interaction is to allow effective operation and control of the machine f ...
must be usable for its target user/audience. Default values for the parameters must be chosen so that they are a good choice for the majority of the users. *
Performance A performance is an act of staging or presenting a play, concert, or other form of entertainment. It is also defined as the action or process of carrying out or accomplishing an action, task, or function. Management science In the work place ...
- The software performs its tasks within a time-frame that is acceptable for the user, and does not require too much memory. * Portability - The software should be usable across a number of different conditions and environments. *
Scalability Scalability is the property of a system to handle a growing amount of work by adding resources to the system. In an economic context, a scalable business model implies that a company can increase sales given increased resources. For example, a ...
- The software adapts well to increasing data or added features or number of users.


Modeling language

A
modeling language A modeling language is any artificial language that can be used to express information or knowledge or systems in a structure that is defined by a consistent set of rules. The rules are used for interpretation of the meaning of components in th ...
is any artificial language that can be used to express information, knowledge or systems in a structure that is defined by a consistent set of rules. These rules are used for interpretation of the components within the structure. A modeling language can be graphical or textual. Examples of graphical modeling languages for software design are: *
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 ...
(ADL) is a language used to describe and represent the
software architecture 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. ...
of a software system. *
Business Process Modeling Notation Business Process Model and Notation (BPMN) is a graphical representation for specifying business processes in a business process model. Originally developed by the Business Process Management Initiative (BPMI), BPMN has been maintained by the ...
(BPMN) is an example of a
Process Modeling The term process model is used in various contexts. For example, in business process modeling the enterprise process model is often referred to as the ''business process model''. Overview Process models are processes of the same nature that a ...
language. * EXPRESS and EXPRESS-G (ISO 10303-11) is an international standard general-purpose data modeling language. *
Extended Enterprise Modeling Language Extended Enterprise Modeling Language (EEML) in software engineering is a modelling language used for Enterprise modelling across a number of layers. Overview Extended Enterprise Modeling Language (EEML) is a modelling language which combines st ...
(EEML) is commonly used for business process modeling across a number of layers. * Flowcharts are schematic representations of algorithms or other step-wise processes. * Fundamental Modeling Concepts (FMC) is modeling language for software-intensive systems. *
IDEF IDEF, initially an abbreviation of ICAM Definition and renamed in 1999 as Integration Definition,IEEE Standard for Functional Modeling Language—Syntax and Semantics for IDEF0, Software Engineering Standards Committee of the IEEE Computer Soci ...
is a family of modeling languages, the most notable of which include
IDEF0 IDEF0, a compound acronym ("Icam DEFinition for Function Modeling", where ICAM is an acronym for "Integrated Computer Aided Manufacturing"), is a function modeling methodology for describing manufacturing functions, which offers a functional model ...
for functional modeling,
IDEF1X Integration DEFinition for information modeling (IDEF1X) is a data modeling language for the development of semantic data models. IDEF1X is used to produce a graphical information model which represents the structure and semantics of information ...
for information modeling, and
IDEF5 IDEF5 (''Integrated Definition for Ontology Description Capture Method'') is a software engineering method to develop and maintain usable, accurate domain ontologies.Perakath C. Benjamin et al. (1994)''IDEF5 Method Report''. Knowledge Based System ...
for modeling
ontologies In computer science and information science, an ontology encompasses a representation, formal naming, and definition of the categories, properties, and relations between the concepts, data, and entities that substantiate one, many, or all domains ...
. * Jackson Structured Programming (JSP) is a method for structured programming based on correspondences between data stream structure and program structure. * LePUS3 is an
object-oriented Object-oriented programming (OOP) is a programming paradigm based on the concept of " objects", which can contain data and code. The data is in the form of fields (often known as attributes or ''properties''), and the code is in the form of p ...
visual Design Description Language and a
formal specification In computer science, formal specifications are mathematically based techniques whose purpose are to help with the implementation of systems and software. They are used to describe a system, to analyze its behavior, and to aid in its design by verif ...
language that is suitable primarily for modeling large object-oriented (
Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's List ...
,
C++ C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...
, C#) programs and design patterns. *
Unified Modeling Language The Unified Modeling Language (UML) is a general-purpose, developmental modeling language in the field of software engineering that is intended to provide a standard way to visualize the design of a system. The creation of UML was originally m ...
(UML) is a general modeling language to describe software both structurally and behaviorally. It has a graphical notation and allows for extension with a
Profile (UML) A profile in the Unified Modeling Language (UML) provides a generic extension mechanism for customizing UML models for particular domains and platforms. Extension mechanisms allow refining standard semantics in strictly additive manner, preventing ...
. *
Alloy (specification language) In computer science and software engineering, Alloy is a declarative specification language for expressing complex structural constraints and behavior in a software system. Alloy provides a simple structural modeling tool based on first-order logic ...
is a general purpose specification language for expressing complex structural constraints and behavior in a software system. It provides a concise language base on first-order relational logic. *
Systems Modeling Language The Systems Modeling Language (SysML) is a general-purpose modeling language for systems engineering applications. It supports the specification, analysis, design, verification and validation of a broad range of systems and systems-of-systems. ...
(SysML) is a new
general-purpose modeling General-purpose modeling (GPM) is the systematic use of a general-purpose modeling language to represent the various facets of an object or a system. Examples of GPM languages are: * The Unified Modeling Language (UML), an industry standard for ...
language for systems engineering. * Service-oriented modeling framework (SOMF)


Design patterns

A software designer or architect may identify a design problem which has been visited and perhaps even solved by others in the past. A template or pattern describing a solution to a common problem is known as a
design pattern A design pattern is the re-usable form of a solution to a design problem. The idea was introduced by the architect Christopher Alexander and has been adapted for various other disciplines, particularly software engineering. The " Gang of Four" b ...
. The reuse of such patterns can help speed up the software development process.


Technique

The difficulty of using the term "design" in relation to software is that in some senses, the source code of a program ''is'' the design for the program that it produces. To the extent that this is true, "software design" refers to the design of the design. Edsger W. Dijkstra referred to this layering of semantic levels as the "radical novelty" of computer programming, and
Donald Knuth Donald Ervin Knuth ( ; born January 10, 1938) is an American computer scientist, mathematician, and professor emeritus at Stanford University. He is the 1974 recipient of the ACM Turing Award, informally considered the Nobel Prize of computer sc ...
used his experience writing
TeX Tex may refer to: People and fictional characters * Tex (nickname), a list of people and fictional characters with the nickname * Joe Tex (1933–1982), stage name of American soul singer Joseph Arrington Jr. Entertainment * ''Tex'', the Italian ...
to describe the futility of attempting to design a program prior to implementing it:


Usage

Software design document A software design description (a.k.a. software design document or SDD; just design document; also Software Design Specification) is a representation of a software design that is to be used for recording design information, addressing various de ...
ation may be reviewed or presented to allow constraints, specifications and even requirements to be adjusted prior to
computer programming Computer programming is the process of performing a particular computation (or more generally, accomplishing a specific computing result), usually by designing and building an executable computer program. Programming involves tasks such as ana ...
. Redesign may occur after review of a programmed
simulation A simulation is the imitation of the operation of a real-world process or system over time. Simulations require the use of Conceptual model, models; the model represents the key characteristics or behaviors of the selected system or proc ...
or
prototype A prototype is an early sample, model, or release of a product built to test a concept or process. It is a term used in a variety of contexts, including semantics, design, electronics, and Software prototyping, software programming. A prototyp ...
. It is possible to design software in the process of programming, without a plan or requirement analysis,Ralph, P., and Wand, Y. A Proposal for a Formal Definition of the Design Concept. In, Lyytinen, K., Loucopoulos, P., Mylopoulos, J., and Robinson, W., (eds.), Design Requirements Engineering: A Ten-Year Perspective: Springer-Verlag, 2009, pp. 103-136 but for more complex projects this would not be considered feasible. A separate design prior to programming allows for
multidisciplinary Interdisciplinarity or interdisciplinary studies involves the combination of multiple academic disciplines into one activity (e.g., a research project). It draws knowledge from several other fields like sociology, anthropology, psychology, ec ...
designers and subject-matter experts (SMEs) to collaborate with highly skilled programmers for software that is both useful and technically sound.


See also

*
Aspect-oriented software development In computing, aspect-oriented programming (AOP) is a programming paradigm that aims to increase modularity by allowing the separation of cross-cutting concerns. It does so by adding behavior to existing code (an advice) ''without'' modifying ...
*
Bachelor of Science in Information Technology A Bachelor of Science in Information Technology, (abbreviated BSIT or B.Sc. IT), is a bachelor's degree awarded for an undergraduate program in the information technology. The degree is normally required in order to work in the Information tec ...
*
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'' ...
*
Design rationale A design rationale is an explicit documentation of the reasons behind decisions made when designing a system or artifact. As initially developed by W.R. Kunz and Horst Rittel, design rationale seeks to provide argumentation-based structure to ...
*
Graphic design Graphic design is a profession, academic discipline and applied art whose activity consists in projecting visual communications intended to transmit specific messages to social groups, with specific objectives. Graphic design is an interdiscipli ...
*
Interaction design Interaction design, often abbreviated as IxD, is "the practice of designing interactive digital products, environments, systems, and services." Beyond the digital aspect, interaction design is also useful when creating physical (non-digital) produ ...
*
Icon design Icon design is the process of designing a graphic symbol that represents some real, fantasy or abstract motive, entity or action. In the context of software applications, an icon often represents a program, a function, data or a collection of data o ...
* Outline of software *
Outline of software development The following outline is provided as an overview of and topical guide to software development: Software development is the development of a software product, which entails computer programming (process of writing and maintaining the source code ...
* Outline of software engineering *
Search-based software engineering Search-based software engineering (SBSE) applies metaheuristic search techniques such as genetic algorithms, simulated annealing and tabu search to software engineering problems. Many activities in software engineering can be stated as optimizatio ...
*
Software Design Description A software design description (a.k.a. software design document or SDD; just design document; also Software Design Specification) is a representation of a software design that is to be used for recording design information, addressing various de ...
(IEEE 1016) *
Software development Software development is the process of conceiving, specifying, designing, programming, documenting, testing, and bug fixing involved in creating and maintaining applications, frameworks, or other software components. Software development invol ...
* User experience *
User interface design User interface (UI) design or user interface engineering is the design of user interfaces for machines and software, such as computers, home appliances, mobile devices, and other electronic devices, with the focus on maximizing usability and the ...
*
Web design Web design encompasses many different skills and disciplines in the production and maintenance of websites. The different areas of web design include web graphic design; user interface design (UI design); authoring, including standardised code a ...
* Zero One Infinity


References

^ {{DEFAULTSORT:Software Design Software engineering Computer occupations