L05-06 Req Eng PDF Requirements Engineering

11/20/2021 Requirements engineering  The requirements are the descriptions of the services Requir...

11/20/2021 Requirements engineering  The requirements are the descriptions of the services Requirements Engineering that a system should provide and the constraints on its operation and implementation.  What is a requirement? Functional and non-functional requirements  It may range from a high-level abstract statement of a service or of a system constraint to a detailed mathematical functional Requirements engineering processes specification. Requirements elicitation  This is inevitable as requirements may serve a dual Requirements specification function  May be the basis for a bid for a contract - therefore must be open Requirements validation to interpretation; Requirements change  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 1 Dr. Noha Adly CSE 322 - Requirements Engineering 2 1 2 Types of requirement User and system requirements a user requirement may be expanded into several system requirements.  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 Dr. Noha Adly CSE 322 - Requirements Engineering 4 3 4  11/20/2021 Readers of different types of requirements specification 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 5 Dr. Noha Adly CSE 322 - Requirements Engineering 6 5 6 Stakeholders in the Mentcare system Agile methods and requirements  Patients whose information is recorded in the system.  Many agile methods argue that producing detailed  Doctors who are responsible for assessing and treating patients. system requirements is a waste of time as requirements  Nurses who coordinate the consultations with doctors and administer change so quickly. some treatments.  The requirements document is therefore always out of  Medical receptionists who manage patients’ appointments. date  IT staff who are responsible for installing and maintaining the system.  Agile methods usually use incremental requirements  A medical ethics manager who must ensure that the system meets engineering and may express requirements as ‘user current ethical guidelines for patient care. stories’  Health care managers who obtain management information from the  This is practical for business systems but problematic for system. systems that require pre-delivery analysis (e.g. critical  Medical records staff who are responsible for ensuring that system systems) or systems developed by several teams. information can be maintained and preserved, and that record keeping procedures have been properly implemented. Dr. Noha Adly CSE 322 - Requirements Engineering 7 Dr. Noha Adly CSE 322 - Requirements Engineering 8 7 8  11/20/2021 Functional and non-functional requirements Functional requirements  Statements of services the system should provide how the system should react to particular inputs Functional and non-functional how the system should behave in particular situations requirements 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 9 Dr. Noha Adly CSE 322 - Requirements Engineering 10 9 10 Functional requirements Requirements imprecision  Describe functionality or system services in detail  Ambiguous requirements may be interpreted in different ways by developers and users.  Functional users requirements - may be high-level statements of what the system should do.  Problems arise when functional requirements are not precisely stated.  Functional systems requirements – describe system  Disputes between customers and developers functions, inputs, outputs, and exceptions in detail.  Delays system delivery and increase cost  Example: Mentcare system functional requirements  Consider the term ‘search’ in requirement 1  A user shall be able to search the appointments lists for all A user shall be able to search the appointments lists for all clinics clinics.  User intention – search for a patient name across all  The system shall generate each day, for each clinic, a list of appointments in all clinics; patients who are expected to attend appointments that day.  Developer interpretation – search for a patient name in an  Each staff member using the system shall be uniquely identified individual clinic. User chooses clinic then search. by his or her 8-digit employee number. Dr. Noha Adly CSE 322 - Requirements Engineering 11 Dr. Noha Adly CSE 322 - Requirements Engineering 12 11 12  11/20/2021 Requirements completeness and consistency Non-functional requirements  In principle, requirements should be both complete and  These define system properties and constraints e.g. consistent. reliability, response time and storage requirements. Constraints are I/O device capability, system  Complete representations, etc.  They should include descriptions of all facilities required.  Process requirements may also be specified mandating  Consistent a particular IDE, programming language or development  There should be no conflicts or contradictions in the descriptions method. of the system facilities.  Non-functional requirements may be more critical than  In practice, it is impossible to produce a complete and functional requirements. If these are not met, the system consistent requirements document for large systems, may be useless. because of system and environmental complexity, and diverse stakeholders Dr. Noha Adly CSE 322 - Requirements Engineering 13 Dr. Noha Adly CSE 322 - Requirements Engineering 14 13 14 Non-functional requirements implementation Non-functional classifications  Non-functional requirements may affect the overall  Product requirements architecture of a system rather than the individual  Requirements which specify constraints on the runtime components. behaviour of the software e.g. execution speed, memory use,  For example, to ensure that performance requirements are met, reliability, acceptable failure rate etc. you may have to organize the system to minimize  Organisational requirements communications between components.  Requirements which are a consequence of organisational  A single non-functional requirement, such as a security policies and procedures e.g. process standards used, requirement, may generate a number of related development process requirements, etc. functional requirements that define system services that  External requirements are required.  Requirements which arise from factors which are external to the  It may also generate requirements that restrict existing system and its development process e.g. interoperability requirements e.g. it may limit access to information in the system requirements, legislative requirements, etc. Dr. Noha Adly CSE 322 - Requirements Engineering 15 Dr. Noha Adly CSE 322 - Requirements Engineering 16 15 16  11/20/2021 Types of Non-functional requirement 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 17 Dr. Noha Adly CSE 322 - Requirements Engineering 18 17 18 Goals and requirements Metrics for specifying nonfunctional requirements  Non-functional requirements may be very difficult to state precisely Property Measure and imprecise requirements may be difficult to verify. Speed Processed transactions/second User/event response time  Stakeholders tend to propose requirements as general goals Screen refresh time  Goal : A general intention of the user such as ease of use. E.g. Size Mbytes The system should be easy to use by medical staff and should be Number of ROM chips organized in such a way that user errors are minimized. Ease of use Training time  Requirements should be written as Verifiable/testable non- Number of help frames functional requirement Reliability Mean time to failure Probability of unavailability A statement using some measure that can be objectively tested. Rate of failure occurrence you should write non-functional requirements quantitatively Availability Medical staff shall be able to use all the system functions after four Robustness Time to restart after failure hours of training. After this training, the average number of errors Percentage of events causing failure made by experienced users shall not exceed two per hour of Probability of data corruption on failure system use. Portability Percentage of target dependent statements Number of target systems Dr. Noha Adly CSE 322 - Requirements Engineering 19 Dr. Noha Adly CSE 322 - Requirements Engineering 20 19 20  11/20/2021 Requirements engineering processes  The processes used for RE vary widely depending on  the application domain  the people involved and  the organisation developing the requirements Requirements Engineering Processes  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 21 Dr. Noha Adly CSE 322 - Requirements Engineering 22 21 22 A spiral view of the requirements engineering process Requirements Elicitation Dr. Noha Adly CSE 322 - Requirements Engineering 23 Dr. Noha Adly CSE 322 - Requirements Engineering 24 23 24  11/20/2021 Requirements elicitation and analysis Problems of requirements elicitation  Sometimes called requirements discovery.  Stakeholders don’t know what they really want.  The aims are to  they may make unrealistic demands because they don’t know what is and isn’t feasible  understand the work that stakeholders do, and  how they might use a new system to help support that work  Stakeholders express requirements in their own terms.  with implicit knowledge of their own work. Requirements  May involve end-users, managers, engineers involved in engineers, may not understand these requirements maintenance, domain experts, trade unions, etc. These are called stakeholders.  Different stakeholders may have conflicting requirements.  Software engineers work with a range of system  Organisational and political factors may influence the stakeholders to find out about: system requirements.  the application domain,  The requirements change during the analysis process.  the services that the system should provide,  New stakeholders may emerge and the business  the system’s operational constraints: system performance, environment may change. hardware constraints, other systems, etc. Dr. Noha Adly CSE 322 - Requirements Engineering 25 Dr. Noha Adly CSE 322 - Requirements Engineering 26 25 26 Process activities The requirements elicitation and analysis process  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 Dr. Noha Adly CSE 322 - Requirements Engineering 28 27 28  11/20/2021 Requirements discovery Interviewing  The process of gathering information about the required  Formal / informal interviews with stakeholders are part of most RE processes. and existing systems and distilling the user and system requirements from this information.  Types of interview  Closed interviews based on pre-determined list of questions  Interaction is with system stakeholders from managers to  Open interviews where various issues are explored with stakeholders. external regulators.  Effective interviewing  Discovery approaches  Normally a mix of closed and open-ended interviewing.  Interviewing: talk to people about what they do  Interviews are good for getting an overall understanding of what  Ethnography (Observation): watch people doing their job to see stakeholders do and how they might interact with the system. what artifacts they use, how they use them etc.  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 29. Dr. Noha Adly CSE 322 - Requirements Engineering 30 29 30 Problems with interviews Ethnography  Application specialists may use language to describe  An observational technique that can be used to understand their work that isn’t easy for the requirements engineer to operational processes and help derive support requirements for understand. these processes  Interviews are not good for understanding domain  it helps discover implicit system requirements that reflect the requirements actual ways that people work  Requirements engineers cannot understand specific domain  It is effective for discovering two types of requirements: terminology;  Requirements that are derived from the way that people actually work  Some domain knowledge is so familiar that people find it hard to rather than the way in which process definitions suggest that they articulate or think that it isn’t worth articulating. ought to work.  Example: for a librarian, it goes without saying that all  Requirements that are derived from cooperation and awareness of acquisitions are catalogued before they are added to the library. However, this may not be obvious to the interviewer. 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 31 Dr. Noha Adly CSE 322 - Requirements Engineering 32 31 32  11/20/2021 Ethnography and prototyping for requirements analysis Stories and scenarios  Ethnography can be combined with prototyping  Scenarios and user stories are real-life examples of how  Prototype development results in unanswered questions a system can be used. which focus the ethnographic analysis.  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 33 Dr. Noha Adly CSE 322 - Requirements Engineering 34 33 34 Photo sharing in the classroom (iLearn) - Story Scenarios  Jack is a primary school teacher in Ullapool (a village in northern Scotland). He  A structured form of user story 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  Stories are effective to describe the big picture, they can 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 then be developed into more specific scenarios. 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  Scenarios should include photographs. However, Jack also needs a photo sharing site as he wants pupils to  A description of the starting situation; take and comment on each others’ photos and to upload scans of old photographs  A description of the normal flow of events; that they may have in their families.  A description of what can go wrong; Jack sends an email to a primary school teachers group, which he is a member of  Information about other concurrent activities; 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  A description of the state when the scenario finishes. 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 Dr. Noha Adly CSE 322 - Requirements Engineering 36 35 36  11/20/2021 Uploading photos (iLearn) - scenario Uploading photos (iLearn) – scenario (cont’d)  INITIAL ASSUMPTION: A user or a group of users have one or  WHAT CAN GO WRONG: more digital photographs to be uploaded to the picture sharing site.  No moderator is associated with the selected project. An email is These are saved on either a tablet or laptop computer. They have automatically generated to the school administrator asking them to successfully logged on to KidsTakePics. nominate a project moderator. Users should be informed that there could be a delay in making their photos visible.  NORMAL: The user chooses upload photos and they are prompted to select the photos to be uploaded on their computer and to select  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 the project name under which the photos will be stored. They should with the same name, rename the photos or cancel the upload. If they also be given the option of inputting keywords that should be chose to re-upload the photos, the originals are overwritten. If they associated with each uploaded photo. Uploaded photos are named chose to rename the photos, a new name is automatically generated by by creating a conjunction of the user name with the filename of the adding a number to the existing file name. photo on the local computer.  OTHER ACTIVITIES: The moderator may be logged on to the system and  On completion of the upload, the system automatically sends an may approve photos as they are uploaded. email to the project moderator asking them to check new content  SYSTEM STATE ON COMPLETION: User is logged on. The selected and generates an on-screen message to the user that this has photos have been uploaded and assigned a status ‘awaiting moderation’. been done. Photos are visible to the moderator and to the user who uploaded them. Dr. Noha Adly CSE 322 - Requirements Engineering 37 Dr. Noha Adly CSE 322 - Requirements Engineering 38 37 38 Scenario for collecting medical history in MentCare Scenario for collecting medical history in MentCare  WHAT CAN GO WRONG:  INITIAL ASSUMPTION: The patient has seen a medical receptionist who has created a record in the system and collected the patient’s personal  The patient’s record does not exist or cannot be found. The nurse should create a new record and record personal information. information (name, address, age, etc.). A nurse is logged on to the system and is collecting medical history.  Patient conditions or medication are not entered in the menu. The nurse should choose the ‘other’ option and enter free text describing the  NORMAL: condition/medication  The nurse searches for the patient by family name. If there is more  Patient cannot/will not provide information on medical history. than one patient with the same surname, the given name (first name The nurse should enter free text recording the patient’s in English) and date of birth are used to identify the patient. inability/unwillingness to provide information.  The nurse chooses the menu option to add medical history. The The system should print the standard exclusion form stating that the lack nurse then follows a series of prompts from the system to enter of information may mean that treatment will be limited or delayed. information about consultations elsewhere on This should be signed and handed to the patient. mental health problems (free text input),  OTHER ACTIVITIES: Record may be consulted but not edited by staff while information is being entered. existing medical conditions (nurse selects conditions from menu), medication currently taken (selected from menu),  SYSTEM STATE ON COMPLETION: User is logged on. The patient record allergies (free text) 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 home life (form). CSE 322 - Requirements Engineering 39 Dr. Noha Adly CSE 322 - Requirements Engineering 40 39 40  11/20/2021 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 Dr. Noha Adly CSE 322 - Requirements Engineering 42 41 42 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 Requirements Specification 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 43 Dr. Noha Adly CSE 322 - Requirements Engineering 44 43 44  11/20/2021 Ways of writing a system requirements specification Requirements and design  In principle, requirements should state what the system Notation Description Natural language The requirements are written using numbered sentences in natural language. should do and the design should describe how it does Each sentence should express one requirement. this. Structured natural The requirements are written in natural language on a standard form or  In practice, requirements and design are inseparable language template. Each field provides information about an aspect of the requirement.  A system architecture may be designed to structure the Design description This approach uses a language like a programming language, but with more requirements; 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  The system may inter-operate with other systems that generate interface specifications. design requirements; which constraint the design and impose Graphical Graphical models, supplemented by text annotations, are used to define the requirements on the new system, notations functional requirements for the system; UML use case and sequence diagrams are commonly used.  The use of a specific architecture to satisfy non-functional Mathematical These notations are based on mathematical concepts such as finite-state requirements may be a domain requirement – such as N-version specifications machines or sets. Although these unambiguous specifications can reduce the programming to achieve reliability ambiguity in a requirements document, most customers don’t understand a formal specification. They cannot check that it represents what they want and  This may be the consequence of a regulatory requirement: are reluctant to accept it as a system contract 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 45 Dr. Noha Adly CSE 322 - Requirements Engineering 46 45 46 Natural language specification Guidelines for writing requirements  Requirements are written as natural language sentences  Invent a standard format and use it for all requirements. supplemented by diagrams and tables.  Use language in a consistent way. Use  Used for writing requirements because it is expressive, intuitive  shall for mandatory requirements, and universal. This means that the requirements can be  should for desirable requirements. understood by users and customers.  Use text highlighting to identify key parts of the  Problems with natural language requirement.  Lack of clarity  Avoid the use of computer jargon, abbreviations and Precision is difficult without making the document difficult to read. acronyms  Requirements confusion  Include an explanation (rationale) of why a requirement Functional and non-functional requirements tend to be mixed-up. is necessary.  Requirements amalgamation Several different requirements may be expressed together. Dr. Noha Adly CSE 322 - Requirements Engineering 47 Dr. Noha Adly CSE 322 - Requirements Engineering 48 47 48  11/20/2021 Ex: requirements for the insulin pump software system Structured specifications 3.2 The system shall measure the blood sugar and  An approach to writing requirements where the freedom deliver insulin, if required, every 10 minutes. (Changes of the requirements writer is limited and requirements in blood sugar are relatively slow so more frequent are written in a standard way. measurement is unnecessary; less frequent  This works well for some types of requirements e.g. measurement could lead to unnecessarily high sugar requirements for embedded control system but is levels.) sometimes too rigid for writing business system requirements. 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 Dr. Noha Adly CSE 322 - Requirements Engineering 50 49 50 Form-based specifications A structured specification of a requirement for insulin pump  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 Dr. Noha Adly CSE 322 - Requirements Engineering 52 51 52  11/20/2021 Tabular specification Tabular specification of computation for an insulin pump  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 Condition Action computations on the rate of change of blood sugar level Sugar level falling (r2 < r1) CompDose = 0 and the tabular specification explains how to calculate Sugar level stable (r2 = r1) CompDose = 0 the insulin requirement for different scenarios. 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 53 Dr. Noha Adly CSE 322 - Requirements Engineering 54 53 54 Use cases Use cases for the Mentcare system  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 Dr. Noha Adly CSE 322 - Requirements Engineering 56 55 56  11/20/2021 Use cases for the Mentcare system The software requirements document  Each use case should be documented with a textual description,  The software requirements document is the official which can be linked to other models in the UML that will develop the statement of what is required of the system developers. scenario in more detail.  For example, a brief description of the Setup Consultation use case  It is called Software Requirement Specification SRS from Figure 4.15 might be:  Should include both Setup consultation allows two or more doctors, working in different  A definition of user requirements and offices, to view the same record at the same time. One doctor initiates  A specification of the system requirements. the consultation by choosing the people involved from a drop-down menu of doctors who are online. The patient record is then displayed  It is NOT a design document. As far as possible, it on their screens but only the initiating doctor can edit the record. In should set of WHAT the system should do rather than addition, a text chat window is created to help coordinate actions. It is HOW it should do it. assumed that a phone conference for voice communication will be separately set up. Dr. Noha Adly CSE 322 - Requirements Engineering 57 Dr. Noha Adly CSE 322 - Requirements Engineering 58 57 58 Users of a requirements document 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 59 Dr. Noha Adly CSE 322 - Requirements Engineering 60 59 60  11/20/2021 The structure of a requirements document – based on The structure of a requirements document – IEEE Standard based on IEEE Standard Chapter Description Chapter Description Preface This should define the expected readership of the document and describe its System This should describe the functional and nonfunctional requirements in more detail. version history, including a rationale for the creation of a new version and a requirements If necessary, further detail may also be added to the nonfunctional requirements. summary of the changes made in each version. specification Interfaces to other systems may be defined. Introduction This should describe the need for the system. It should briefly describe the System models This might include graphical system models showing the relationships between system’s functions and explain how it will work with other systems. It should the system components and the system and its environment. Examples of also describe how the system fits into the overall business or strategic possible models are object models, data-flow models, or semantic data models. objectives of the organization commissioning the software. System evolution This should describe the fundamental assumptions on which the system is based, Glossary This should define the technical terms used in the document. You should not and any anticipated changes due to hardware evolution, changing user needs, make assumptions about the experience or expertise of the reader. 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. 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 Appendices These should provide detailed, specific information that is related to the may use natural language, diagrams, or other notations that are application being developed; for example, hardware and database descriptions. understandable to customers. Product and process standards that must be Hardware requirements define the minimal and optimal configurations for the followed should be specified. system. Database requirements define the logical organization of the data used by the system and the relationships between data. System architecture This chapter should present a high-level overview of the anticipated system architecture, showing the distribution of functions across system modules. Index Several indexes to the document may be included. As well as a normal alphabetic Architectural components that are reused should be highlighted. index, there may be an index of diagrams, an index of functions, and so on. Dr. Noha Adly CSE 322 - Requirements Engineering 61 Dr. Noha Adly CSE 322 - Requirements Engineering 62 61 62 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 Validation  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 63 Dr. Noha Adly CSE 322 - Requirements Engineering 64 63 64  11/20/2021 Requirements checking Requirements validation techniques  Validity. Does the system provide the functions which Requirements reviews best support the customer’s needs?  Systematic manual analysis of the requirements.  Consistency. Are there any requirements conflicts? Prototyping  Completeness. Are all functions required by the  Using an executable model of the system to check customer included? requirements.  Realism. Can the requirements be implemented given Test-case generation available budget and technology  Developing tests for requirements to check testability  Verifiability. Can the requirements be checked?  If a test is difficult to design, this usually means that the requirements will be difficult to implement  write a set of tests that can demonstrate that the delivered system meets each specified requirement  Developing tests from the user requirements before code is written is an integral part of Agile Dr. Noha Adly CSE 322 - Requirements Engineering 65 Dr. Noha Adly CSE 322 - Requirements Engineering 66 65 66 Requirements reviews Review checks  Regular reviews should be held while the requirements  Verifiability definition is being formulated.  Is the requirement realistically testable?  Both client and contractor staff should be involved in  Comprehensibility reviews.  Is the requirement properly understood?  Reviews may be formal (with completed documents) or  Traceability informal. Good communications between developers,  Is the origin of the requirement clearly stated? customers and users can resolve problems at an early  Adaptability stage.  Can the requirement be changed without a large impact on other requirements? Dr. Noha Adly CSE 322 - Requirements Engineering 67 Dr. Noha Adly CSE 322 - Requirements Engineering 68 67 68  11/20/2021 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 Requirements 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 69 Dr. Noha Adly CSE 322 - Requirements Engineering 70 69 70 Requirements evolution 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 71 Dr. Noha Adly CSE 322 - Requirements Engineering 72 71 72  11/20/2021 Requirements management planning Requirements change management  Establishes the level of requirements management detail  Deciding if a requirements change should be accepted that is required.  Problem analysis and change specification During this stage, the problem or the change proposal is analyzed  Requirements management decisions: to check that it is valid. This analysis is fed back to the change  Requirements identification Each requirement must be uniquely requestor who may respond with a more specific requirements identified so that it can be cross-referenced with other requirements. change proposal, or decide to withdraw the request.  A change management process This is the set of activities that  Change analysis and costing assess the impact and cost of changes. The effect of the proposed change is assessed using traceability information and general knowledge of the system requirements.  Traceability policies These policies define the relationships between Once this analysis is completed, a decision is made whether or not each requirement and between the requirements and the system to proceed with the requirements change. design that should be recorded.  Change implementation  Tool support Tools that may be used range from specialized The requirements document and, where necessary, the system requirements management systems to spreadsheets and simple design and implementation, are modified. Ideally, the document database systems. should be organized so that changes can be easily implemented. Dr. Noha Adly CSE 322 - Requirements Engineering 73 Dr. Noha Adly CSE 322 - Requirements Engineering 74 73 74 Requirements change management Key points  The requirements engineering process is an iterative 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. Dr. Noha Adly CSE 322 - Requirements Engineering 75 Dr. Noha Adly CSE 322 - Requirements Engineering 76 75 76  11/20/2021 Key points  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.  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. Dr. Noha Adly CSE 322 - Requirements Engineering 77 77