Requirements Engineering (CSE 322) PDF

12/23/2023 Requirements Engineering Functional and non-functional requirements Requirements engineering processes Requirements elicitation Requirements specification Requirements validation...

12/23/2023 Requirements Engineering Functional and non-functional requirements Requirements engineering processes Requirements elicitation Requirements specification Requirements validation Requirements change Dr. Noha Adly CSE 322 - Requirements Engineering 1 1  12/23/2023 Requirements engineering  The requirements are the descriptions of the services that a system should provide and the constraints on its operation and implementation.  What is a requirement?  It may range from a high-level abstract statement of a service or of a system constraint to a detailed mathematical functional specification.  This is inevitable as 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. Dr. Noha Adly CSE 322 - Requirements Engineering 2 2  12/23/2023 Types of requirement  User requirements  Statements in natural language plus diagrams of the services the system provides and its operational constraints. Written for customers.  System requirements  A structured document setting out detailed descriptions of the system’s functions, services and operational constraints.  Defines exactly what should be implemented  May be part of a contract between client and contractor. Dr. Noha Adly CSE 322 - Requirements Engineering 3 3  12/23/2023 User and system requirements a user requirement may be expanded into several system requirements. Dr. Noha Adly CSE 322 - Requirements Engineering 4 4  12/23/2023 Readers of different types of requirements specification Dr. Noha Adly CSE 322 - Requirements Engineering 5 5  12/23/2023 System stakeholders  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 Dr. Noha Adly CSE 322 - Requirements Engineering 6 6  12/23/2023 Stakeholders in the Mentcare system  Patients whose information is recorded in the system.  Doctors who are responsible for assessing and treating patients.  Nurses who coordinate the consultations with doctors and administer some treatments.  Medical receptionists who manage patients’ appointments.  IT staff who are responsible for installing and maintaining the system.  A medical ethics manager who must ensure that the system meets current ethical guidelines for patient care.  Health care managers who obtain management information from the system.  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. Dr. Noha Adly CSE 322 - Requirements Engineering 7 7  12/23/2023 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. Dr. Noha Adly CSE 322 - Requirements Engineering 8 8  12/23/2023 Functional and non-functional requirements Dr. Noha Adly CSE 322 - Requirements Engineering 9 9  12/23/2023 Functional and non-functional requirements Functional requirements  Statements of services the system should provide how the system should react to particular inputs how the system should behave in particular situations May state what the system should not do Non-functional requirements  Constraints on the services or functions offered by the system such as timing constraints constraints on the development process standards, reliability, availability, etc.  Often apply to the system as a whole rather than individual features or services. Dr. Noha Adly CSE 322 - Requirements Engineering 10 10  12/23/2023 Functional requirements  Describe functionality or system services in detail  Functional users requirements - may be high-level statements of what the system should do.  Functional systems requirements – describe system functions, inputs, outputs, and exceptions in detail.  Example: Mentcare system functional requirements  A user shall be able to search the appointments lists for all clinics.  The system shall generate each day, for each clinic, a list of patients who are expected to attend appointments that day.  Each staff member using the system shall be uniquely identified by his or her 8-digit employee number. Dr. Noha Adly CSE 322 - Requirements Engineering 11 11  12/23/2023 Requirements imprecision  Ambiguous requirements may be interpreted in different ways by developers and users.  Problems arise when functional requirements are not precisely stated.  Disputes between customers and developers  Delays system delivery and increase cost  Consider the term ‘search’ in requirement 1 A user shall be able to search the appointments lists for all clinics  User intention – search for a patient name across all appointments in all clinics;  Developer interpretation – search for a patient name in an individual clinic. User chooses clinic then search. Dr. Noha Adly CSE 322 - Requirements Engineering 12 12  12/23/2023 Requirements completeness and consistency  In principle, requirements should be both complete and consistent.  Complete  They should include descriptions of all facilities required.  Consistent  There should be no conflicts or contradictions in the descriptions of the system facilities.  In practice, it is impossible to produce a complete and consistent requirements document for large systems, because of system and environmental complexity, and diverse stakeholders Dr. Noha Adly CSE 322 - Requirements Engineering 13 13  12/23/2023 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. Dr. Noha Adly CSE 322 - Requirements Engineering 14 14  12/23/2023 Non-functional requirements implementation  Non-functional requirements may affect the overall architecture of a system rather than the individual components.  For example, to ensure that performance requirements are met, you may have to organize the system to minimize communications between components.  A single non-functional requirement, such as a security requirement, may generate a number of related functional requirements that define system services that are required.  It may also generate requirements that restrict existing requirements e.g. it may limit access to information in the system Dr. Noha Adly CSE 322 - Requirements Engineering 15 15  12/23/2023 Non-functional classifications  Product requirements  Requirements which specify constraints on the runtime behaviour of the software e.g. execution speed, memory use, reliability, acceptable failure rate etc.  Organisational requirements  Requirements which are a consequence of organisational policies and procedures e.g. process standards used, development process requirements, etc.  External requirements  Requirements which arise from factors which are external to the system and its development process e.g. interoperability requirements, legislative requirements, etc. Dr. Noha Adly CSE 322 - Requirements Engineering 16 16  12/23/2023 Types of Non-functional requirement Dr. Noha Adly CSE 322 - Requirements Engineering 17 17  12/23/2023 Examples of nonfunctional requirements in Mentcare system Product requirement The Mentcare system shall be available to all clinics 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. Dr. Noha Adly CSE 322 - Requirements Engineering 18 18  12/23/2023 Goals and requirements  Non-functional requirements may be very difficult to state precisely and imprecise requirements may be difficult to verify.  Stakeholders tend to propose requirements as general goals  Goal : A general intention of the user such as ease of use. E.g. The system should be easy to use by medical staff and should be organized in such a way that user errors are minimized.  Requirements should be written as Verifiable/testable non- functional requirement A statement using some measure that can be objectively tested. you should write non-functional requirements quantitatively Medical staff shall be able to use all the system functions after four hours of training. After this training, the average number of errors made by experienced users shall not exceed two per hour of system use. Dr. Noha Adly CSE 322 - Requirements Engineering 19 19  12/23/2023 Metrics for specifying nonfunctional requirements Property Measure Speed Processed transactions/second User/event response time Screen refresh time Size Mbytes Number of ROM chips Ease of use Training time Number of help frames Reliability Mean time to failure Probability of unavailability Rate of failure occurrence Availability Robustness Time to restart after failure Percentage of events causing failure Probability of data corruption on failure Portability Percentage of target dependent statements Number of target systems Dr. Noha Adly CSE 322 - Requirements Engineering 20 20  12/23/2023 Requirements Engineering Processes Dr. Noha Adly CSE 322 - Requirements Engineering 21 21  12/23/2023 Requirements engineering processes  The processes used for RE vary widely depending on  the application domain  the people involved and  the organisation developing the requirements  However, there are a number of generic activities common to all processes  Requirements elicitation;  Requirements analysis;  Requirements validation;  Requirements management.  In practice, RE is an iterative activity in which these processes are interleaved. Dr. Noha Adly CSE 322 - Requirements Engineering 22 22  12/23/2023 A spiral view of the requirements engineering process Dr. Noha Adly CSE 322 - Requirements Engineering 23 23  12/23/2023 Requirements Elicitation Dr. Noha Adly CSE 322 - Requirements Engineering 24 24  12/23/2023 Requirements elicitation and analysis  Sometimes called requirements discovery.  The aims are to  understand the work that stakeholders do, and  how they might use a new system to help support that work  May involve end-users, managers, engineers involved in maintenance, domain experts, trade unions, etc. These are called stakeholders.  Software engineers work with a range of system stakeholders to find out about:  the application domain,  the services that the system should provide,  the system’s operational constraints: system performance, hardware constraints, other systems, etc. Dr. Noha Adly CSE 322 - Requirements Engineering 25 25  12/23/2023 Problems of requirements elicitation  Stakeholders don’t know what they really want.  they may make unrealistic demands because they don’t know what is and isn’t feasible  Stakeholders express requirements in their own terms.  with implicit knowledge of their own work. Requirements engineers, may not understand these requirements  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. Dr. Noha Adly CSE 322 - Requirements Engineering 26 26  12/23/2023 Process activities  Requirements discovery  Interacting with stakeholders to discover their requirements. Domain requirements are also discovered at this stage.  Requirements classification and organisation  Groups related requirements and organises them into coherent clusters.  Prioritisation and negotiation  Prioritising requirements and resolving requirements conflicts.  Requirements specification  Requirements are documented and input into the next round of the spiral. Dr. Noha Adly CSE 322 - Requirements Engineering 27 27  12/23/2023 The requirements elicitation and analysis process Dr. Noha Adly CSE 322 - Requirements Engineering 28 28  12/23/2023 Requirements discovery  The process of gathering information about the required and existing systems and distilling the user and system requirements from this information.  Interaction is with system stakeholders from managers to external regulators.  Discovery approaches  Interviewing: talk to people about what they do  Ethnography (Observation): watch people doing their job to see what artifacts they use, how they use them etc. Dr. Noha Adly CSE 322 - Requirements Engineering 29 29  12/23/2023 Interviewing  Formal / informal interviews with stakeholders are part of most RE processes.  Types of interview  Closed interviews based on pre-determined list of questions  Open interviews where various issues are explored with stakeholders.  Effective interviewing  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.  Be open-minded, avoid pre-conceived ideas about the requirements and are 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 rather than simply asking them what they want Dr..Noha Adly CSE 322 - Requirements Engineering 30 30  12/23/2023 Problems with interviews  Application specialists may use language to describe their work that isn’t easy for the requirements engineer to understand.  Interviews are not good for understanding domain requirements  Requirements engineers cannot understand specific domain terminology;  Some domain knowledge is so familiar that people find it hard to articulate or think that it isn’t worth articulating.  Example: for a librarian, it goes without saying that all acquisitions are catalogued before they are added to the library. However, this may not be obvious to the interviewer. Dr. Noha Adly CSE 322 - Requirements Engineering 31 31  12/23/2023 Ethnography  An observational technique that can be used to understand operational processes and help derive support requirements for these processes  it helps discover implicit system requirements that reflect the actual ways that people work  It is effective for discovering two types of requirements:  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. Awareness of what other people are doing leads to changes in the ways in which we do things.  Ethnography is effective for understanding existing processes but cannot identify new features that should be added to a system. Dr. Noha Adly CSE 322 - Requirements Engineering 32 32  12/23/2023 Ethnography and prototyping for requirements analysis  Ethnography can be combined with prototyping  Prototype development results in unanswered questions which focus the ethnographic analysis. Dr. Noha Adly CSE 322 - Requirements Engineering 33 33  12/23/2023 Stories and scenarios  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.  Can be used in interviews to develop more requirements  Stories are narrated text presenting high level description  Scenarios are structured with specific information collected Dr. Noha Adly CSE 322 - Requirements Engineering 34 34  12/23/2023 Photo sharing in the classroom (iLearn) - Story  Jack is a primary school teacher in Ullapool (a village in northern Scotland). He has decided that a class project should be focused around the fishing industry in the area, looking at the history, development and economic impact of fishing. As part of this, pupils are asked to gather and share reminiscences from relatives, use newspaper archives and collect old photographs related to fishing and fishing communities in the area. Pupils use an iLearn wiki to gather together fishing stories and SCRAN (a history resources site) to access newspaper archives and photographs. However, Jack also needs a photo sharing site as he wants pupils to take and comment on each others’ photos and to upload scans of old photographs that they may have in their families. Jack sends an email to a primary school teachers group, which he is a member of to see if anyone can recommend an appropriate system. Two teachers reply and both suggest that he uses KidsTakePics, a photo sharing site that allows teachers to check and moderate content. As KidsTakePics is not integrated with the iLearn authentication service, he sets up a teacher and a class account. He uses the iLearn setup service to add KidsTakePics to the services seen by the pupils in his class so that when they log in, they can immediately use the system to upload photos from their mobile devices and class computers. Dr. Noha Adly CSE 322 - Requirements Engineering 35 35  12/23/2023 Scenarios  A structured form of user story  Stories are effective to describe the big picture, they can then be developed into more specific scenarios.  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. Dr. Noha Adly CSE 322 - Requirements Engineering 36 36  12/23/2023 Uploading photos (iLearn) - scenario  INITIAL ASSUMPTION: A user or a group of users have one or more digital photographs to be uploaded to the picture sharing site. These are saved on either a tablet or laptop computer. They have successfully logged on to KidsTakePics.  NORMAL: The user chooses upload photos and they are prompted to select the photos to be uploaded on their computer and to select the project name under which the photos will be stored. They should also be given the option of inputting keywords that should be associated with each uploaded photo. Uploaded photos are named by creating a conjunction of the user name with the filename of the photo on the local computer.  On completion of the upload, the system automatically sends an email to the project moderator asking them to check new content and generates an on-screen message to the user that this has been done. Dr. Noha Adly CSE 322 - Requirements Engineering 37 37  12/23/2023 Uploading photos (iLearn) – scenario (cont’d)  WHAT CAN GO WRONG:  No moderator is associated with the selected project. An email is automatically generated to the school administrator asking them to nominate a project moderator. Users should be informed that there could be a delay in making their photos visible.  Photos with the same name have already been uploaded by the same user. The user should be asked if they wish to re-upload the photos with the same name, rename the photos or cancel the upload. If they chose to re-upload the photos, the originals are overwritten. If they chose to rename the photos, a new name is automatically generated by adding a number to the existing file name.  OTHER ACTIVITIES: The moderator may be logged on to the system and may approve photos as they are uploaded.  SYSTEM STATE ON COMPLETION: User is logged on. The selected photos have been uploaded and assigned a status ‘awaiting moderation’. Photos are visible to the moderator and to the user who uploaded them. Dr. Noha Adly CSE 322 - Requirements Engineering 38 38  12/23/2023 Scenario for collecting medical history in MentCare  INITIAL ASSUMPTION: The patient has seen a medical receptionist who has created a record in the system and collected the patient’s personal information (name, address, age, etc.). A nurse is logged on to the system and is collecting medical history.  NORMAL:  The nurse searches for the patient by family name. If there is more than one patient with the same surname, the given name (first name in English) and date of birth are used to identify the patient.  The nurse chooses the menu option to add medical history. The nurse then follows a series of prompts from the system to enter information about consultations elsewhere on mental health problems (free text input), existing medical conditions (nurse selects conditions from menu), medication currently taken (selected from menu), allergies (free text) Dr. Noha Adly home life (form). CSE 322 - Requirements Engineering 39 39  12/23/2023 Scenario for collecting medical history in MentCare  WHAT CAN GO WRONG:  The patient’s record does not exist or cannot be found. The nurse should create a new record and record personal information.  Patient conditions or medication are not entered in the menu. The nurse should choose the ‘other’ option and enter free text describing the condition/medication  Patient cannot/will not provide information on medical history. The nurse should enter free text recording the patient’s inability/unwillingness to provide information. The system should print the standard exclusion form stating that the lack of information may mean that treatment will be limited or delayed. This should be signed and handed to the patient.  OTHER ACTIVITIES: Record may be consulted but not edited by staff while information is being entered.  SYSTEM STATE ON COMPLETION: User is logged on. The patient record including medical history is entered in the database, a record is added to the system log showing the start and end time of the session and the nurse involved. Dr. Noha Adly CSE 322 - Requirements Engineering 40 40  12/23/2023 Use Case ID: Description: Primary Actors: Priority: Trigger: Precondition: Basic Path: Alternative Paths: Post condition Exception Paths Includes Frequency of use Assumptions Notes & issues Dr. Noha Adly CSE 322 - Requirements Engineering 41 41  12/23/2023 Dr. Noha Adly CSE 322 - Requirements Engineering 42 42  12/23/2023 Requirements Specification Dr. Noha Adly CSE 322 - Requirements Engineering 43 43  12/23/2023 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. Dr. Noha Adly CSE 322 - Requirements Engineering 44 44  12/23/2023 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 language template. Each field provides information about an aspect of the requirement. Design description This approach uses a language like a programming language, but with more languages abstract 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 Graphical models, supplemented by text annotations, are used to define the notations 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 specifications machines or 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 Dr. Noha Adly CSE 322 - Requirements Engineering 45 45  12/23/2023 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; which constraint the design and impose requirements on the new system,  The use of a specific architecture to satisfy non-functional requirements may be a domain requirement – such as N-version programming to achieve reliability  This may be the consequence of a regulatory requirement: An external regulator who needs to certify that the system is safe may specify that an already certified architectural design be used. Dr. Noha Adly CSE 322 - Requirements Engineering 46 46  12/23/2023 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.  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. Dr. Noha Adly CSE 322 - Requirements Engineering 47 47  12/23/2023 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, abbreviations and acronyms  Include an explanation (rationale) of why a requirement is necessary. Dr. Noha Adly CSE 322 - Requirements Engineering 48 48  12/23/2023 Ex: requirements for the insulin pump software system 3.2 The system shall measure the blood sugar and deliver insulin, if required, every 10 minutes. (Changes in blood sugar are relatively slow so more frequent measurement is unnecessary; less frequent measurement could lead to unnecessarily high sugar levels.) 3.6 The system shall run a self-test routine every minute with the conditions to be tested and the associated actions defined in Table 1. (A self-test routine can discover hardware and software problems and alert the user to the fact that the normal operation may be impossible.) Dr. Noha Adly CSE 322 - Requirements Engineering 49 49  12/23/2023 Structured specifications  An approach to writing requirements where the freedom of the requirements writer is limited and requirements are written in a standard way.  This works well for some types of requirements e.g. requirements for embedded control system but is sometimes too rigid for writing business system requirements. Dr. Noha Adly CSE 322 - Requirements Engineering 50 50  12/23/2023 Form-based specifications  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. Dr. Noha Adly CSE 322 - Requirements Engineering 51 51  12/23/2023 A structured specification of a requirement for insulin pump Dr. Noha Adly CSE 322 - Requirements Engineering 52 52  12/23/2023 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. Dr. Noha Adly CSE 322 - Requirements Engineering 53 53  12/23/2023 Tabular specification of computation for an insulin pump Condition Action Sugar level falling (r2 < r1) CompDose = 0 Sugar level stable (r2 = r1) CompDose = 0 Sugar level increasing and rate of increase decreasing CompDose = 0 ((r2 – r1) < (r1 – r0)) Sugar level increasing and rate of increase stable or CompDose=round((r2 – r1)/4) increasing If rounded result = 0 then ((r2 – r1) ≥ (r1 – r0)) CompDose= MinimumDose Dr. Noha Adly CSE 322 - Requirements Engineering 54 54  12/23/2023 Use cases  Use cases are a way of describing interactions between users and a system using a graphical model and structured text  Use-cases are fundamental feature of the UML.  Use cases identify the actors in an interaction and name the type of the interaction.  Additional information is added for describing the interaction itself  Textual description  High-level graphical model supplemented by more detailed tabular description  UML sequence diagrams may be used to add detail to use-cases by showing the sequence of event processing in the system.  A set of use cases should describe all possible interactions with the system. Dr. Noha Adly CSE 322 - Requirements Engineering 55 55  12/23/2023 Use cases for the Mentcare system Dr. Noha Adly CSE 322 - Requirements Engineering 56 56  12/23/2023 Use cases for the Mentcare system  Each use case should be documented with a textual description, which can be linked to other models in the UML that will develop the scenario in more detail.  For example, a brief description of the Setup Consultation use case from Figure 4.15 might be: Setup consultation allows two or more doctors, working in different offices, to view the same record at the same time. One doctor initiates the consultation by choosing the people involved from a drop-down menu of doctors who are online. The patient record is then displayed on their screens but only the initiating doctor can edit the record. In addition, a text chat window is created to help coordinate actions. It is assumed that a phone conference for voice communication will be separately set up. Dr. Noha Adly CSE 322 - Requirements Engineering 57 57  12/23/2023 The software requirements document  The software requirements document is the official statement of what is required of the system developers.  It is called Software Requirement Specification SRS  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. Dr. Noha Adly CSE 322 - Requirements Engineering 58 58  12/23/2023 Users of a requirements document Dr. Noha Adly CSE 322 - Requirements Engineering 59 59  12/23/2023 Requirements document variability  Diversity of users requires compromises between  communicating the requirements to customers  defining the requirements in detail for developers and testers  including information about possible system evolution, which can help system designers avoid restrictive design decisions  Level of details in requirements document depends on type of system and the approach to development used.  Critical systems need detailed requirements because safety and security have to be analyzed  When the system is to be outsourced, the system specifications need to be detailed and precise.  If an in house, iterative development process is used, the requirements document can be much less detailed and any ambiguities can be resolved during development of the system. Dr. Noha Adly CSE 322 - Requirements Engineering 60 60  12/23/2023 The structure of a requirements document – based on IEEE Standard 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 definition system requirements 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. Dr. Noha Adly CSE 322 - Requirements Engineering 61 61  12/23/2023 The structure of a requirements document – based on IEEE Standard Chapter Description System This should describe the functional and nonfunctional requirements in more detail. requirements If necessary, further detail may also be added to the nonfunctional requirements. specification 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. Dr. Noha Adly CSE 322 - Requirements Engineering 62 62  12/23/2023 Requirements Validation Dr. Noha Adly CSE 322 - Requirements Engineering 63 63  12/23/2023 Requirements validation  Concerned with demonstrating that the requirements define the system that the customer really wants.  It overlaps with analysis as it is concerned with finding problems with the requirements.  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. Dr. Noha Adly CSE 322 - Requirements Engineering 64 64  12/23/2023 Requirements checking  Validity. Does the system provide the functions 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?  write a set of tests that can demonstrate that the delivered system meets each specified requirement Dr. Noha Adly CSE 322 - Requirements Engineering 65 65  12/23/2023 Requirements validation techniques Requirements reviews  Systematic manual analysis of the requirements. Prototyping  Using an executable model of the system to check requirements. Test-case generation  Developing tests for requirements to check testability  If a test is difficult to design, this usually means that the requirements will be difficult to implement  Developing tests from the user requirements before code is written is an integral part of Agile Dr. Noha Adly CSE 322 - Requirements Engineering 66 66  12/23/2023 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. Dr. Noha Adly CSE 322 - Requirements Engineering 67 67  12/23/2023 Review checks  Verifiability  Is the requirement realistically testable?  Comprehensibility  Is the requirement properly understood?  Traceability  Is the origin of the requirement clearly stated?  Adaptability  Can the requirement be changed without a large impact on other requirements? Dr. Noha Adly CSE 322 - Requirements Engineering 68 68  12/23/2023 Requirements Change Dr. Noha Adly CSE 322 - Requirements Engineering 69 69  12/23/2023 Changing requirements  The business and technical environment of the system always changes after installation.  New hardware may be introduced  It may be necessary to interface the system with other systems  business priorities may change  new legislation and regulations may be introduced  The people who pay for a system and the users of that system are rarely the same people.  System customers impose requirements because of organizational and budgetary constraints. These may conflict with end-user requirements and, after delivery, new features may have to be added for user support if the system is to meet its goals.  Large systems usually have a diverse user community, with many users having different requirements and priorities that may be conflicting or contradictory.  The final system requirements are inevitably a compromise between them and, with experience, it is often discovered that the balance of support given to different users has to be changed Dr. Noha Adly CSE 322 - Requirements Engineering 70 70  12/23/2023 Requirements evolution Dr. Noha Adly CSE 322 - Requirements Engineering 71 71  12/23/2023 Requirements management  Requirements management is the 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.  You need to  keep track of individual requirements and  maintain links between dependent requirements so that you can assess the impact of requirements changes.  You need to establish a formal process for making change proposals and linking these to system requirements. Dr. Noha Adly CSE 322 - Requirements Engineering 72 72  12/23/2023 Requirements management planning  Establishes the level of requirements management detail that is required.  Requirements management decisions:  Requirements identification Each requirement must be uniquely identified so that it can be cross-referenced with other requirements.  A change management process This is the set of activities that assess the impact and cost of changes.  Traceability policies These policies define the relationships between each requirement and between the requirements and the system design that should be recorded.  Tool support Tools that may be used range from specialized requirements management systems to spreadsheets and simple database systems. Dr. Noha Adly CSE 322 - Requirements Engineering 73 73  12/23/2023 Requirements change management  Deciding if a requirements change should be accepted  Problem analysis and change specification During this stage, the problem or the change proposal is analyzed to check that it is valid. This analysis is fed back to the change requestor who may respond with a more specific requirements change proposal, or decide to withdraw the request.  Change analysis and costing The effect of the proposed change is assessed using traceability information and general knowledge of the system requirements. Once this analysis is completed, a decision is made whether or not to proceed with the requirements change.  Change implementation The requirements document and, where necessary, the system design and implementation, are modified. Ideally, the document should be organized so that changes can be easily implemented. Dr. Noha Adly CSE 322 - Requirements Engineering 74 74  12/23/2023 Requirements change management Dr. Noha Adly CSE 322 - Requirements Engineering 75 75