CSE241/CMM341 Foundations of Software Engineering Requirements Engineering 2023 PDF

CSE241/CMM341 Foundations of Software Engineering https://www.kenotom.com/wp-content/uploads/2018/06/Requirements-Engineering-1.jpg TOPIC 4: Requirements Engineering CSE241 Course Content 2 Foundations 1. Introduction to Software Engineerin...

CSE241/CMM341 Foundations of Software Engineering https://www.kenotom.com/wp-content/uploads/2018/06/Requirements-Engineering-1.jpg TOPIC 4: Requirements Engineering CSE241 Course Content 2 Foundations 1. Introduction to Software Engineering of Software 2. Software Processes Engineering 3. Agile Software Development 4. Requirements Engineering 5. System Modeling 6. Software Design Strategies and Methods 7. Architectural Design & Implementation 8. Software Testing 9. Software Evolution 10. Project Management 11. Project planning 12. Quality Management 13. Configuration Management  3 Topic 4: Requirements Engineering Functional and Non-functional Requirements Requirements Engineering Processes Can anyone tell Requirements Elicitation me the link of this Requirements Specification topic to the Software Process? Requirements validation Requirements Change Learning outcomes By the end of this topic, you should be able to: 01 02 03 04 4 Understand the Understand the Understand the main Understand why concepts of user and differences between requirements requirements system requirements functional and non- engineering activities management is and why these functional software of elicitation, analysis necessary and how it requirements should requirements and validation, and the supports other be written in different relationships between requirements ways. these activities engineering activities.  5 Requirements engineering (RE) Requirements engineering - The process of finding System requirements are the out, analyzing, descriptions of documenting and what the system should do (system services) checking these constraints on system operations services and constraints.  What is a Requirement? Definition a high-level, abstract statement that a system should provide or a constraint on a system. Requirements may serve a dual function: May be the basis for a bid for a contract - therefore must be open to interpretation; May be the basis for the contract itself - therefore must be defined in detail; Both these statements may be called requirements. 6  Requirements Abstraction (Davis) “If a company wishes to let a contract for a large software development project, it must define its needs in a sufficiently abstract way that a solution is not pre-defined. The requirements must be written so that several contractors can bid for the contract, offering, perhaps, different ways of meeting the client organization’s needs. Once a contract has been awarded, the contractor must write a system definition for the client in more detail so that the client understands and can validate what the software will do.” 7 Types of requirement 8 User requirements Statements in natural language plus diagrams of the services the system provides and its operational constraints. Written for customers. High-level abstract requirements System requirements A structured document setting out detailed descriptions of the system’s functions, services and operational constraints. Defines what should be implemented. May be part of a contract between client and contractor. Detailed system descriptions  Case Study: A mental health care patient management system A medical information system that maintains information about patients suffering from mental health problems and the treatments that they have received. 10 Readers of different types of requirements specification Any person or organization who is affected by the system in some way and so who has a legitimate interest. Stakeholder types End users System managers System owners External stakeholders 11  Examples of system stakeholders 1. Patients whose information is recorded in the system and relatives of these patients. 2. IT staff who are responsible for installing and maintaining the system. 3. Medical records staff who are responsible for ensuring that system information can be maintained and preserved, and that record keeping procedures have been properly implemented. 4. Medical receptionists who manage patients’ appointments. 5. Nurses who coordinate the consultations with doctors and administer some treatments. 6. Doctors who are responsible for assessing and treating patients. 7. Health care managers who obtain management information from the system. 8. A medical ethics manager who must ensure that the system meets current ethical guidelines for patient care. 12  Agile Methods and Requirements ▪ Many agile methods argue that producing detailed system requirements is a waste of time as requirements change so quickly. ▪ The requirements document is therefore always out of date. ▪ Agile methods usually use incremental requirements engineering and may express requirements as ‘user stories’ ▪ This is practical for business systems but problematic for systems that require pre-delivery analysis (e.g. critical systems) or systems developed by several teams. 13  14 Topic 4: Requirements Engineering Functional and Non-functional Requirements Requirements Engineering Processes Requirements Elicitation Requirements Specification Requirements validation Requirements Change  Functional and Non-functional Requirements https://www.modernrequirements.com/wp-content/uploads/2019/08/Functional-and-Non-Functional-Requirements.png  Functional and Non-functional 16 Requirements Functional Requirements Non-functional Requirements Statements of services the system should Cultivate one-to-one customer provide, how the system should react to service with robust ideas particular inputs and how the system should Maximize timely deliverables behave in particular situations. for real-time schemas May state what the system should not do.  Describe functionality or system services. Depend on the type of software, expected users and the type of system where the Functional software is used. Requirements Functional user requirements may be high- level statements of what the system should do. Functional system requirements should describe the system services in detail. 17  Example of Functional Requirements REQ1 REQ2 REQ3 A user shall be able to The system shall Each staff member using search the appointments generate each day, for the system shall be lists for all clinics. each clinic, a list of uniquely identified by his patients who are or her 8-digit employee expected to attend number. appointments that day. 18  Requirements Imprecision Problems arise when functional requirements are not precisely stated. Ambiguous requirements may be interpreted in different ways by developers and users. 19  Requirements Imprecision Problems arise when functional requirements are not precisely stated. Ambiguous requirements may be interpreted in different ways by developers and users. Consider the term ‘search’ in REQ1 User interpretation – search for a patient name across all appointments in all clinics; Developer interpretation – search for a patient name in an individual clinic. The user chooses clinic and then search. 20  Requirements Completeness and Consistency In principle, requirements should be In practice, because of system and both complete and consistent. environmental complexity, it is impossible to produce a complete and consistent Complete requirements document. They should include descriptions of all facilities required. Consistent There should be no conflicts or contradictions in the descriptions of the system facilities. 21  Non-functional Requirements These define system properties and constraints e.g. reliability, response time and storage requirements. Constraints are I/O device capability, system representations, etc. Process requirements may also be specified mandating a particular IDE, programming language or development method. Non-functional requirements may be more critical than functional requirements. If these are not met, the system may be useless. 22  Non-functional Requirements Implementation For example, to ensure that performance Non-functional requirements may affect the requirements are met, you may have to organize the overall architecture of a system rather system to minimize communications between than the individual components. components. A single non-functional requirement, such as a security requirement, may generate a It may also generate requirements that restrict number of related functional requirements existing requirements. that define system services that are required. 23  Types of Non-functional Requirement 24  Non-functional Classifications Organisational Product requirements External requirements requirements Requirements which specify Requirements which are a Requirements which arise that the delivered product consequence of from factors which are must behave in a particular organisational policies and external to the system and its way e.g. execution speed, procedures e.g. process development process e.g. reliability, etc. standards used, interoperability requirements, implementation legislative requirements, etc. requirements, etc. 25  Examples of Non-functional Product requirement The Mentcare system shall be available to all clinics Requirements during normal working hours (Mon–Fri, 0830–17.30). Downtime within normal working hours shall not exceed five seconds in any one day. Organizational requirement Users of the Mentcare system shall authenticate themselves using their health authority identity card. External requirement The system shall implement patient privacy provisions as set out in HStan-03-2006-priv. 26  Goals Vs Requirements Non-functional requirements may be very difficult to state precisely and imprecise requirements may be difficult to verify. Goal A general intention of the user such as ease of use. Verifiable non-functional requirement A statement using some measure that can be objectively tested. Goals are helpful to developers as they convey the intentions of the system users. 27  Example of Usability Requirements Goal Testable non-functional requirement The system should be easy to use by Medical staff shall be able to use all the medical staff and should be organized system functions after four hours of in such a way that user errors are training. After this training, the average number of errors made by experienced minimized. users shall not exceed two per hour of system use. 28  29 Topic 4: Requirements Engineering Functional and Non-functional Requirements Requirements Engineering Processes Requirements Elicitation Requirements Specification Requirements validation Requirements Change  Requirements Engineering Processes ▪ Common generic activities : ▫ Requirements elicitation; ▫ Requirements analysis; ▫ Requirements validation; ▫ Requirements management. ▪ In practice, RE is an iterative activity in which these processes are interleaved. 30  A Spiral View Of The Requirements Engineering Process E F F O R T 31  32 Topic 4: Requirements Engineering Functional and Non-functional Requirements Requirements Engineering Processes Requirements Elicitation Requirements Specification Requirements validation Requirements Change Requirements Elicitation  Requirements Elicitation ▪ to understand the work that stakeholders do and how they might use a new system to help support that work ▪ Find out : ▫ application domain ▫ work activities ▫ services ▫ system features ▫ the required performance of the system ▫ hardware constraints 34  Problems of Requirements Elicitation ▪ Stakeholders don’t know what they really want. ▪ Stakeholders express requirements in their own terms. ▪ Different stakeholders may have conflicting requirements. ▪ Organisational and political factors may influence the system requirements. ▪ The requirements change during the analysis process. New stakeholders may emerge and the business environment may change. 35 https://thumbs.dreamstime.com/b/stakeholders-concept-web-vector-infographics-icons-government-manager- customers-trade-unions-investor-creditor-society-236934868.jpg https://www.consultationmanager.com/wp-content/uploads/2022/05/Identify-and-prioritise-key-stakeholder-relationships.png  The requirements elicitation and analysis process The cycle end when the requirements document has been produced 36  Process Activities in Requirements Elicitation Requirements Requirements Requirements Requirements discovery classification and prioritization and specification organization negotiation interacting with Unstructured collection prioritize requirements Produce early draft of stakeholders of the of requirements, and finding the software system to discover groups related resolve requirements requirements their requirements requirements are conflicts through documents Domain requirements organize into coherent negotiation Document as input into are also discovered clusters. the next round of the spiral 37  Requirements Elicitation Techniques Two fundamental approaches: ▫ Interviewing - talk to people about what they do. ▫ Observation or ethnography -watch people doing their job to see what artifacts they use, how they use them, and so on. https://b-buildingbusiness.com/wp-content/uploads/2020/10/impact-interview-01.png 38  Interviewing Conducted in formal or informal ways https://blog-consumer.glassdoor.com/app/uploads/sites/2/50-most-common-interview-questions.png Types of interview – Closed interviews based on pre-determined list of questions – Open interviews where various issues are explored with stakeholders. Effective interviewing – Be open-minded – avoid pre-conceived ideas about the requirements – willing to listen to stakeholders. – Prompt the interviewee to get discussions going using a springboard question, a requirements proposal, or by working together on a prototype system. 39  Interviews in Practice Normally a mix of closed and open-ended interviewing. Interviews are good for getting an overall understanding of what stakeholders do and how they might interact with the system. Interviewers need to be open-minded without pre-conceived ideas of what the system should do You need to prompt the use to talk about the system by suggesting requirements rather than simply asking them what they want. 40 https://resources.workable.com/wp-content/uploads/2018/05/prepare-interviews-featured.png  Ethnography ▪ an observational technique that can be used to understand operational processes and help derive requirements for software ▪ A social scientist spends a considerable time observing and analysing how people actually work. ▪ People do not have to explain or articulate their work. ▪ Social and organisational factors of importance may be observed. https://uxstudioteam.com/ux-blog/wp-content/uploads/2020/05/UXstudio-Ethnographic-research_Hero-1-1-720x420.jpg 41  Scope of Ethnography ▪ Requirements that are derived from the way that people actually work rather than the way in which process definitions suggest that they ought to work. ▪ Requirements that are derived from cooperation and awareness of other people’s activities. Limitation ▪ Ethnography is effective for understanding existing processes but cannot identify new features that should be added to a system. https://www.epicpeople.org/wp-content/uploads/2022/09/ReD-Associates-EPIC2022-Perspective-Wordpress.png 42  Ethnography and Prototyping for Requirements Analysis 43 Stories and Scenarios (Agile Methods) Scenarios and user stories are real-life examples of how a system can be used. Stories and scenarios are a description of how a system may be used for a particular task. Because they are based on a practical situation, stakeholders can relate to them and can comment on their situation with respect to the story. https://miro.medium.com/max/1400/1*-bwYrRg6vpox7nBemwvllw.png 44  User Stories ▪ A user story is a form of software system requirement that has become quite popular in Agile Methodologies such as Extreme Programming and Scrum. ▪ Unlike more traditional methods such as a System Requirements Specification or Use Case Diagrams, the emphasis in these methodologies is simplicity and changeability. ▪ The attributes of a good user story are: ▫ Written using language that can be easily understood by the customer and end user ▫ Short enough that it consists of a few sentences and can fit onto a small card (read or electronic) ▫ Focused enough that they describe small increments of functionality that can be completed in several days or weeks ▫ Frequently changed based on discussions with the customer as the functionality becomes better understood 45  Scenarios ▪ A structured form of user story ▪ Scenarios should include ▫ A description of the starting situation; ▫ A description of the normal flow of events; ▫ A description of what can go wrong; ▫ Information about other concurrent activities; ▫ A description of the state when the scenario finishes. 46  Examples of user stories 47  Examples of user stories 48  Examples of user stories 49 https://www.justinmind.com/blog/user-story-examples/  User story template Structured form of a user story - with detailed situation descriptions 50  Examples of user stories 51  Case Study: A mental health care patient management system A medical information system that maintains information about patients suffering from mental health problems and the treatments that they have received.  Features of system Individual care Patient monitoring Administrative reporting management The system regularly The system generates create records for patients, monitors the records of monthly management edit the information in the patients that are involved in reports system, view patient history, treatment and issues and so on. warnings, if possible, problems are detected. 53  Example of functional requirements REQ1 REQ2 REQ3 A user shall be able to search the The system shall generate each Each staff member using the appointments lists for all clinics. day, for each clinic, a list of system shall be uniquely patients who are expected to identified by his or her 8-digit attend appointments that day. employee number. 54  System 55 See and reveals Doctor Patients Describes illness Make reports Describe medicine and treatments  56 Topic 4: Requirements Engineering Functional and Non-functional Requirements Requirements Engineering Processes Requirements Elicitation Requirements Specification Requirements validation Requirements Change  Requirements Specification ▪ The process of writing down the user and system requirements in a requirements document. ▪ User requirements have to be understandable by end-users and customers who do not have a technical background. ▪ System requirements are more detailed requirements and may include more technical information. ▪ The requirements may be part of a contract for the system development ▫ It is therefore important that these are as complete as possible. 57  Ways of writing a system requirements specification Notation Description Natural language The requirements are written using numbered sentences in natural language. Each sentence should express one requirement. Structured natural The requirements are written in natural language on a standard form or template. Each language field provides information about an aspect of the requirement. Design description This approach uses a language like a programming language, but with more abstract languages features to specify the requirements by defining an operational model of the system. This approach is now rarely used although it can be useful for interface specifications. Graphical notations Graphical models, supplemented by text annotations, are used to define the functional requirements for the system; UML use case and sequence diagrams are commonly used. Mathematical These notations are based on mathematical concepts such as finite-state machines or specifications sets. Although these unambiguous specifications can reduce the ambiguity in a requirements document, most customers don’t understand a formal specification. They cannot check that it represents what they want and are reluctant to accept it as a system contract 58  Requirements and design ▪ In principle, requirements should state what the system should do and the design should describe how it does this. ▪ In practice, requirements and design are inseparable ▫ A system architecture may be designed to structure the requirements; ▫ The system may inter-operate with other systems that generate design requirements; ▫ The use of a specific architecture to satisfy non-functional requirements may be a domain requirement. ▫ This may be the consequence of a regulatory requirement. 59  Natural language specification ▪ Requirements are written as natural language sentences supplemented by diagrams and tables. ▪ Used for writing requirements because it is expressive, intuitive and universal. This means that the requirements can be understood by users and customers. https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcSQ8YP3EzMqx2OATzU9QXjYISgrsi2nOeMh3g&usqp=CAU 60  Guidelines for writing requirements ▪ Invent a standard format and use it for all requirements. ▪ Use language in a consistent way. Use shall for mandatory requirements, should for desirable requirements. ▪ Use text highlighting to identify key parts of the requirement. ▪ Avoid the use of computer jargon. ▪ Include an explanation (rationale) of why a requirement is necessary. https://cdn.searchenginejournal.com/wp-content/uploads/2020/06/how-natural-language-generation-changes-the-seo-game-5ee20b31cd108-1520x800.png 61  Problems with natural language ▪ Lack of clarity ▫ Precision is difficult without making the document difficult to read. ▪ Requirements confusion ▫ Functional and non-functional requirements tend to be mixed-up. ▪ Requirements amalgamation ▫ Several different requirements may be expressed together. 62  63 Structured specifications An approach to writing This works well for some types requirements where the of requirements e.g. freedom of the requirements requirements for embedded writer is limited and control system but is requirements are written in a sometimes too rigid for writing standard way. business system requirements. Format used for specifying functional requirements 64 Definition of the function or entity. Description of inputs and where they come from. Description of outputs and where they go to. Information about the information needed for the computation and other entities used. Description of the action to be taken. Pre and post conditions (if appropriate). The side effects (if any) of the function. Presentation title 65 Presentation title 66  67 Tabular specification Used to supplement natural language. Particularly useful when you have to define a number of possible alternative courses of action. For example, the insulin pump systems bases its computations on the rate of change of blood sugar level and the tabular specification explains how to calculate the insulin requirement for different scenarios.  68 USE CASES Use cases are a technique for capturing, modeling, and specifying the requirements of a system. A use case corresponds to a set of behaviors that the system may perform in interaction with its actors, and which produces an observable result that contributes to its goals.  69 Use cases Use-cases are a kind of scenario that are included in the UML. Use cases identify the actors in an interaction and which describe the interaction itself. A set of use cases should describe all possible interactions with the system. High-level graphical model supplemented by a more detailed tabular description (Chapter 5). UML sequence diagrams may be used to add detail to use-cases by showing the sequence of event processing in the system.  An example of use case diagram 70  71 The software requirements document The software requirements document is the official statement of what is required of the system developers. Should include both a definition of user requirements and a specification of the system requirements. It is NOT a design document. As far as possible, it should set of WHAT the system should do rather than HOW it should do it.  Users of a requirements document 72  73 Requirements document variability Information in requirements document depends on type of system and the approach to development used. Systems developed incrementally will, typically, have less detail in the requirements document. Requirements documents standards have been designed e.g. IEEE standard. These are mostly applicable to the requirements for large systems engineering projects.  The structure of a requirements document – 1/2 Chapter Description Preface This should define the expected readership of the document and describe its version history, including a rationale for the creation of a new version and a summary of the changes made in each version. Introduction This should describe the need for the system. It should briefly describe the system’s functions and explain how it will work with other systems. It should also describe how the system fits into the overall business or strategic objectives of the organization commissioning the software. Glossary This should define the technical terms used in the document. You should not make assumptions about the experience or expertise of the reader. User requirements Here, you describe the services provided for the user. The nonfunctional system requirements definition should also be described in this section. This description may use natural language, diagrams, or other notations that are understandable to customers. Product and process standards that must be followed should be specified. System architecture This chapter should present a high-level overview of the anticipated system architecture, showing the distribution of functions across system modules. Architectural components that are reused should be highlighted. 74  The structure of a requirements document – 2/2 Chapter Description System requirements This should describe the functional and nonfunctional requirements in more detail. If specification necessary, further detail may also be added to the nonfunctional requirements. Interfaces to other systems may be defined. System models This might include graphical system models showing the relationships between the system components and the system and its environment. Examples of possible models are object models, data-flow models, or semantic data models. System evolution This should describe the fundamental assumptions on which the system is based, and any anticipated changes due to hardware evolution, changing user needs, and so on. This section is useful for system designers as it may help them avoid design decisions that would constrain likely future changes to the system. Appendices These should provide detailed, specific information that is related to the application being developed; for example, hardware and database descriptions. Hardware requirements define the minimal and optimal configurations for the system. Database requirements define the logical organization of the data used by the system and the relationships between data. Index Several indexes to the document may be included. As well as a normal alphabetic index, there may be an index of diagrams, an index of functions, and so on. 75  76 Topic 4: Requirements Engineering Functional and Non-functional Requirements Requirements Engineering Processes Requirements Elicitation Requirements Specification Requirements validation Requirements Change  Requirements Validation ▪ Concerned with demonstrating that the requirements define the system that the customer really wants. ▪ Requirements error costs are high so validation is very important ▫ Fixing a requirements error after delivery may cost up to 100 times the cost of fixing an implementation error. requirements define the system that the customer really wants 77  Requirements checking Does the system provide the functions Validity. which best support the customer’s needs? Consistency. Are there any requirements conflicts? Completeness. Are all functions required by the customer included? Realism. Can the requirements be implemented given available budget and technology Verifiability. Can the requirements be checked? 78  79 Requirements Validation Techniques Systematic manual analysis of the Requirements reviews requirements. Using an executable model of the system to Prototyping check requirements. Covered in Chapter 2. Developing tests for requirements to check Test-case generation testability.  Requirements reviews ▪ Regular reviews should be held while the requirements definition is being formulated. ▪ Both client and contractor staff should be involved in reviews. ▪ Reviews may be formal (with completed documents) or informal. Good communications between developers, customers and users can resolve problems at an early stage. 80  Review checks 81 Verifiability Is the requirement realistically testable? Comprehensibility Is the requirement properly understood? Traceability Is the origin of the requirement clearly stated? Can the requirement be changed without a large Adaptability impact on other requirements?  82 Topic 4: Requirements Engineering Functional and Non-functional Requirements Requirements Engineering Processes Requirements Elicitation Requirements Specification Requirements validation Requirements Change  Reasons for Changing requirements New hardware may be introduced, it may be necessary to interface the The business and technical environment of system with other systems, business priorities may change (with the system always changes after consequent changes in the system support required), and new legislation installation. and regulations may be introduced that the system must necessarily abide by. System customers impose requirements because of organizational and The people who pay for a system and the budgetary constraints. These may conflict with end-user requirements users of that system are rarely the same and, after delivery, new features may have to be added for user support if people. the system is to meet its goals. The final system requirements are inevitably a compromise between them Large systems usually have a diverse user and, with experience, it is often discovered that the balance of support community, with many users having given to different users has to be changed. different requirements and priorities that may be conflicting or contradictory. 83  Requirements evolution 84  85 Requirements management Process of managing changing requirements during the requirements engineering process and system development. New requirements emerge as a system is being developed and after it has gone into use. keep track of individual requirements and maintain links between dependent requirements to assess the impact of Therefore, it is required to : requirements changes. establish a formal process for making change proposals and linking these to system requirements.  Requirements management planning ▪ Establishes the level of requirements management detail that is required. ▪ Issues need to decide: Each requirement must be uniquely identified so that it can be cross- Requirements identification referenced with other requirements. A change management process set of activities that assess the impact and cost of changes. define the relationships between each requirement and between the Traceability policies requirements and the system design that should be recorded. Tools that may be used range from specialist requirements Tool support management systems to spreadsheets and simple database systems. 86 Requirements management tools The requirements should be maintained in a secure, managed data store that is accessible Requirements storage to everyone involved in the requirements engineering process. Tools can keep track of suggested changes Change management and responses to these suggestions. Allows possible relationships between Traceability management requirements to be discovered. 87  Requirements change management process The problem or the change The effect of the proposed The requirements document, proposal is analyzed to check its change is assessed using the system design and validity. This analysis is fed back traceability information and implementation, are to the change requestor who general knowledge of the modified. may respond with a more system requirements. Once specific requirements change this analysis is completed, a proposal, or decide to withdraw decision is made whether or the request. not to proceed with the 88 requirements change. Presentation title 89 Key points (1/4) SUMMARY ▪ Requirements for a software system set out what the system should do and define constraints on its operation and implementation. At ▪ Functional requirements are statements of the services that the system must provide or are descriptions of how some computations must be carried out. ▪ Non-functional requirements often constrain the system being developed and the development process being used. ▪ They often relate to the emergent properties of the system and therefore apply to the system as a whole. Presentation title 90 Key points (2/4) ▪ The requirements engineering process is an iterative At process that includes requirements elicitation, specification and validation. ▪ Requirements elicitation is an iterative process that can be represented as a spiral of activities – requirements discovery, requirements classification and organization, requirements negotiation and requirements documentation. ▪ You can use a range of techniques for requirements elicitation including interviews and ethnography. User stories and scenarios may be used to facilitate discussions. Key points (3/4) ▪ Requirements specification is the process of formally documenting the user and system requirements and creating a software requirements document. ▪ The software requirements document is an agreed statement of the system requirements. It should be organized so that both system customers and software developers can use it. Key points (4/4) ▪ Requirements validation is the process of checking the requirements for validity, consistency, completeness, realism and verifiability. ▪ Business, organizational and technical changes inevitably lead to changes to the requirements for a software system. Requirements management is the process of managing and controlling these changes.