Software Engineering Body of Knowledge (v3) (2014) (811503), страница 81
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In the testretest method, we simply apply the measurementmethod to the same subjects twice. The correlation coefficient between the first and second setof measurement results gives the reliability of themeasurement method.4. Engineering Design[5*, c1s2, c1s3, c1s4]A product’s life cycle costs are largely influencedby the design of the product. This is true for manufactured products as well as for software products.The design of a software product is guided bythe features to be included and the quality attributes to be provided.
It is important to note thatsoftware engineers use the term “design” withintheir own context; while there are some commonalities, there are also many differences betweenengineering design as discussed in this sectionand software engineering design as discussed inthe Software Design KA. The scope of engineering design is generally viewed as much broaderthan that of software design.
The primary aim ofthis section is to identify the concepts needed todevelop a clear understanding regarding the process of engineering design.Many disciplines engage in problem solvingactivities where there is a single correct solution. In engineering, most problems have manysolutions and the focus is on finding a feasiblesolution (among the many alternatives) thatbest meets the needs presented. The set of possible solutions is often constrained by explicitly imposed limitations such as cost, availableresources, and the state of discipline or domainknowledge.
In engineering problems, sometimesthere are also implicit constraints (such as thephysical properties of materials or laws of physics) that also restrict the set of feasible solutionsfor a given problem.4.1. Engineering Design in EngineeringEducationThe importance of engineering design in engineering education can be clearly seen by the highexpectations held by various accreditation bodies for engineering education. Both the Canadian Engineering Accreditation Board and theAccreditation Board for Engineering and Technology (ABET) note the importance of includingengineering design in education programs.The Canadian Engineering AccreditationBoard includes requirements for the amount ofengineering design experience/coursework thatis necessary for engineering students as well asqualifications for the faculty members who teachsuch coursework or supervise design projects.Their accreditation criteria states:Engineering Foundations 15-9Design: An ability to design solutions forcomplex, open-ended engineering problems and to design systems, componentsor processes that meet specified needs withappropriate attention to health and safetyrisks, applicable standards, and economic,environmental, cultural and societal considerations.
[8, p12]In a similar manner, ABET defines engineeringdesign asthe process of devising a system, component, or process to meet desired needs. Itis a decision-making process (often iterative), in which the basic sciences, mathematics, and the engineering sciences areapplied to convert resources optimally tomeet these stated needs.
[9, p4]Thus, it is clear that engineering design is avital component in the training and education forall engineers. The remainder of this section willfocus on various aspects of engineering design.4.2. Design as a Problem Solving Activity[5*, c1s4, c2s1, c3s3]It is to be noted that engineering design is primarily a problem solving activity. Design problemsare open ended and more vaguely defined.
Thereare usually several alternative ways to solve thesame problem. Design is generally considered tobe a wicked problem—a term first coined by HorstRittel in the 1960s when design methods were asubject of intense interest. Rittel sought an alternative to the linear, step-by-step model of the designprocess being explored by many designers anddesign theorists and argued that most of the problems addressed by the designers are wicked problems. As explained by Steve McConnell, a wickedproblem is one that could be clearly defined onlyby solving it or by solving part of it.
This paradoximplies, essentially, that a wicked problem has tobe solved once in order to define it clearly and thensolved again to create a solution that works. Thishas been an important insight for software designers for several decades [10*, c5s1].4.3. Steps Involved in Engineering Design[7*, c4]Engineering problem solving begins when aneed is recognized and no existing solution willmeet that need. As part of this problem solving,the design goals to be achieved by the solutionshould be identified. Additionally, a set of acceptance criteria must be defined and used to determine how well a proposed solution will satisfythe need. Once a need for a solution to a problemhas been identified, the process of engineeringdesign has the following generic steps:a)define the problemb)gather pertinent informationc)generate multiple solutionsd)analyze and select a solutione)implement the solutionAll of the engineering design steps are iterative, and knowledge gained at any step in theprocess may be used to inform earlier tasks andtrigger an iteration in the process.
These steps areexpanded in the subsequent sections.a. Define the problem. At this stage, the customer’s requirements are gathered. Specific information about product functions and features are alsoclosely examined. This step includes refining theproblem statement to identify the real problem tobe solved and setting the design goals and criteriafor success.The problem definition is a crucial stage inengineering design.
A point to note is that thisstep is deceptively simple. Thus, enough caremust be taken to carry out this step judiciously. Itis important to identify needs and link the successcriteria with the required product characteristics.It is also an engineering task to limit the scopeof a problem and its solution through negotiationamong the stakeholders.b. Gather pertinent information.
At this stage,the designer attempts to expand his/her knowledge about the problem. This is a vital, yet oftenneglected, stage. Gathering pertinent informationcan reveal facts leading to a redefinition of the15-10 SWEBOK® Guide V3.0problem—in particular, mistakes and false startsmay be identified. This step may also involve thedecomposition of the problem into smaller, moreeasily solved subproblems.While gathering pertinent information, caremust be taken to identify how a product may beused as well as misused. It is also important tounderstand the perceived value of the product/service being offered. Included in the pertinentinformation is a list of constraints that must besatisfied by the solution or that may limit the setof feasible solutions.c. Generate multiple solutions. During this stage,different solutions to the same problem are developed.
It has already been stated that design problems have multiple solutions. The goal of thisstep is to conceptualize multiple possible solutions and refine them to a sufficient level of detailthat a comparison can be done among them.d. Analyze and select a solution. Once alternativesolutions have been identified, they need to be analyzed to identify the solution that best suits the current situation. The analysis includes a functionalanalysis to assess whether the proposed designwould meet the functional requirements. Physicalsolutions that involve human users often includeanalysis of the ergonomics or user friendliness ofthe proposed solution.
Other aspects of the solution—such as product safety and liability, an economic or market analysis to ensure a return (profit)on the solution, performance predictions and analysis to meet quality characteristics, opportunitiesfor incorrect data input or hardware malfunctions,and so on—may be studied. The types and amountof analysis used on a proposed solution are dependent on the type of problem and the needs that thesolution must address as well as the constraintsimposed on the design.e.
Implement the solution. The final phase of thedesign process is implementation. Implementation refers to development and testing of theproposed solution. Sometimes a preliminary,partial solution called a prototype may be developed initially to test the proposed design solution under certain conditions. Feedback resultingfrom testing a prototype may be used either torefine the design or drive the selection of an alternative design solution. One of the most important activities in design is documentation of thedesign solution as well as of the tradeoffs for thechoices made in the design of the solution.
Thiswork should be carried out in a manner such thatthe solution to the design problem can be communicated clearly to others.The testing and verification take us back to thesuccess criteria. The engineer needs to devisetests such that the ability of the design to meet thesuccess criteria is demonstrated. While designing the tests, the engineer must think throughdifferent possible failure modes and then designtests based on those failure modes. The engineermay choose to carry out designed experiments toassess the validity of the design.5. Modeling, Simulation, and Prototyping[5*, c6] [11*, c13s3] [12*, c2s3.1]Modeling is part of the abstraction process usedto represent some aspects of a system.
Simulation uses a model of the system and provides ameans of conducting designed experiments withthat model to better understand the system, itsbehavior, and relationships between subsystems,as well as to analyze aspects of the design. Modeling and simulation are techniques that can beused to construct theories or hypotheses about thebehavior of the system; engineers then use thosetheories to make predictions about the system.Prototyping is another abstraction process wherea partial representation (that captures aspects ofinterest) of the product or system is built.
A prototype may be an initial version of the system butlacks the full functionality of the final version.5.1. ModelingA model is always an abstraction of some realor imagined artifact. Engineers use models inmany ways as part of their problem solvingactivities. Some models are physical, such as amade-to-scale miniature construction of a bridgeor building. Other models may be nonphysicalrepresentations, such as a CAD drawing of a cogor a mathematical model for a process. Modelshelp engineers reason and understand aspects ofEngineering Foundations 15-11a problem. They can also help engineers understand what they do know and what they don’tknow about the problem at hand.There are three types of models: iconic, analogic, and symbolic.
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