Software Requirements engineering
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The document discusses key concepts in software requirements engineering including requirements, requirements engineering activities, and types of requirements. It defines a requirement as a statement that captures stakeholder needs and must be met for a system to solve a problem. Requirements engineering involves eliciting, analyzing, specifying, and managing requirements throughout the system development lifecycle. There are functional requirements that define what a system should do and non-functional requirements relating to qualities like performance, security, and usability. The document outlines common requirements engineering processes such as elicitation, analysis, specification, and management.
![7
Statistics from NIST Report
•NIST (National Institute of Standards and Technology) has
published a comprehensive (309 pages) and very interesting
report on project statistics and experiences based on data
from a large number of software projects1
• 70% of the defects are introduced in the specification phase
• 30% are introduced later in the technical solution process
• Only 5% of the specification inadequacies are corrected in the
specification phase
• 95% are detected later in the project or after delivery where the cost
for correction on average is 22 times higher compared to a correction
directly during the specification effort
• The NIST report concludes that extensive testing is essential, however
testing detects the dominating specification errors late in the process
[1] http://www.nist.gov/public_affairs/releases/n02-10.htm (May 2002)](https://image.slidesharecdn.com/requirementsengineering-210217134511/85/Software-Requirements-engineering-7-320.jpg)
![15
Non-Functional Requirements (NFR) (1)
•Non-functional requirements are important
• If they are not met, the system is useless
• Non-functional requirements may be very difficult to state precisely
(especially at the beginning) and imprecise requirements may be
difficult to verify
•They are sometimes called quality requirements, quality of
service, or extra-functional requirements.
•Three main categories 1:
• Performance requirements reflecting: usability, efficiency, reliability,
maintainability and reusability (note: also security requirements)
• Response time, throughput
• Resource usage
• Reliability, availability
• Recovery from failure
• Allowances for maintainability and enhancement
• Allowances for reusability
[1] Lethbridge and Laganière, Object Oriented Software Engineering: Practical Software Development using UML and Java, 2005](https://image.slidesharecdn.com/requirementsengineering-210217134511/85/Software-Requirements-engineering-15-320.jpg)
![36
Problem Domain and System-to-be
A domain model should
be reusable
(Michael Jackson, 1995)
Diagram also showing activities [Bray]
Diagram showing existing and future situation
[Lamsweerde]
better: problem domain (as-is
and to-be)
Problem domain with system-to-be [Bray]](https://image.slidesharecdn.com/requirementsengineering-210217134511/85/Software-Requirements-engineering-36-320.jpg)
![46
The Requirements Analyst1
•Plays an essential communication role
• Talks to users: application domain
• Talks to developers: technical domain
• Translates user requirements into functional requirements and quality
goals
•Needs many capabilities
• Interviewing and listening skills
• Facilitation and interpersonal skills
• Writing and modeling skills
• Organizational ability
•RE is more than just modeling…
This is a social activity!
[1] Karl Wiegers, In Search of Excellent Requirements](https://image.slidesharecdn.com/requirementsengineering-210217134511/85/Software-Requirements-engineering-46-320.jpg)
Software Requirements engineering
- 1. Software Requirements Engineering by Md. Shafiuzzaman Assistant Professor, Dept. of CSE, JUST
- 2. 2 What are “Requirements”? •A requirement is: • Capturing the purpose of a system •An expression of the ideas to be embodied in the system or application under development • A statement about the proposed system that all stakeholders agree must be made true in order for the customer’s problem to be adequately solved • Short and concise piece of information • Says something about the system • All the stakeholders have agreed that it is valid • It helps solve the customer’s problem
- 3. 3 What is “Requirements Engineering”? •Requirements Engineering (RE) is: • The activity of development, elicitation, specification, analysis, and management of the stakeholder requirements, which are to be met by a new or evolving system • RE is concerned with identifying the purpose of a software system… and the contexts in which it will be used • How/where the system will be used • Big picture is important • Captures real world needs of stakeholders affected by a software system and expresses them as artifacts that can be implemented by a computing system • Bridge to design and construction • How to communicate and negotiate? • Is anything lost in the translation between different worlds?
- 4. 4 Requirements Engineering Activities Elicitation Analysis Specification Verification Source: Larry Boldt, Trends in Requirements Engineering People-Process-Technology, Technology Builders, Inc., 2001 Requirements Inception Requirements Management Requirements Engineering Requirements Development
- 5. 5 About these RE Activities… • Inception • Start the process (business need, market opportunity, great idea, ...), business case, feasibility study, system scope, risks, etc. • Requirements elicitation • Requirements discovered through consultation with stakeholders • Requirements analysis and negotiation • Requirements are analyzed and conflicts resolved through negotiation • Requirements specification • A precise requirements document is produced • Requirements validation • The requirements document is checked for consistency and completeness • Requirements management • Needs and contexts evolve, and so do requirements!
- 6. 6 General Problems with the Requirements Process •Lack of the right expertise (software engineers, domain experts, etc.) •Initial ideas are often incomplete, wildly optimistic, and firmly entrenched in the minds of the people leading the acquisition process •Difficulty of using complex tools and diverse methods associated with requirements gathering may negate the anticipated benefits of a complete and detailed approach
- 7. 7 Statistics from NIST Report •NIST (National Institute of Standards and Technology) has published a comprehensive (309 pages) and very interesting report on project statistics and experiences based on data from a large number of software projects1 • 70% of the defects are introduced in the specification phase • 30% are introduced later in the technical solution process • Only 5% of the specification inadequacies are corrected in the specification phase • 95% are detected later in the project or after delivery where the cost for correction on average is 22 times higher compared to a correction directly during the specification effort • The NIST report concludes that extensive testing is essential, however testing detects the dominating specification errors late in the process [1] http://www.nist.gov/public_affairs/releases/n02-10.htm (May 2002)
- 8. 8 • Distribution of Defects • Distribution of Effort to Fix Defects Code 7% Other 10% Design 27% Requirements 56% Code 1% Other 4% Design 13% Requirements 82% Why Focus on Requirements ? Source: Martin & Leffinwell
- 10. 10 So Many “Requirements”… (1) •A goal is an objective or concern that guides the RE process. It can be used to discover and evaluate functional and non- functional requirements • A goal is not yet a requirement… •Note: All requirements must be verifiable (by some test, inspection, audit etc.) •A functional requirement is a requirement defining functions of the system under development • Describes what the system should do •A non-functional requirement is a requirement that is not functional. This includes many different kinds of requirements. – Therefore one often considers the following sub-categories:
- 11. 11 Different types of non-functional requirements •Performance requirements, characterizing system properties such as expected performance, capacity, reliability, robustness, usability, etc. •Design constraints (also called process requirements), providing constraints on how the system should be designed and built – related to development process, documentation, programming language, maintainability, etc. •Commercial constraints, such as development time frame and costs.
- 12. 12 So Many “Requirements”… (2) •A user requirement is a desired goal or function that a user and other stakeholders expect the system to achieve • Does not necessarily become a system requirement •Application domain requirement (sometimes called business rules) are requirements derived from business practices within a given industrial sector, or in a given company, or defined by government regulations or standards. • May lead to system requirements. Can be functional or non-functional •Problem domain requirements should be satisfied within the problem domain in order to satisfy some of the goals •System requirements are the requirements for the system to be built, as a whole • A system is a collection of interrelated components working together towards some common objective (may be software, mechanical, electrical and electronic hardware and be operated by people) • Systems Engineering is a multidisciplinary approach to systems development – software is only a part (but often the problematic part)
- 13. 13 Functional Requirements •What inputs the system should accept •What outputs the system should produce •What data the system should store other systems might use •What computations the system should perform •The timing and synchronization of the above •Depend on the type of software, expected users, and the type of system where the software is used •Functional user requirements may be high-level statements of what the system should do, but functional system requirements should describe the system services in detail
- 14. 14 Examples of Functional Requirements •The user shall be able to search either all of the initial set of databases or select a subset from it. •The system shall provide appropriate viewers for the user to read documents in the document store. •Every order shall be allocated a unique identifier (ORDER_ID) which the user shall be able to copy to the account’s permanent storage area. Note: not all requirements on this and following slides are high quality requirements but are typical requirements found too often in documents
- 15. 15 Non-Functional Requirements (NFR) (1) •Non-functional requirements are important • If they are not met, the system is useless • Non-functional requirements may be very difficult to state precisely (especially at the beginning) and imprecise requirements may be difficult to verify •They are sometimes called quality requirements, quality of service, or extra-functional requirements. •Three main categories 1: • Performance requirements reflecting: usability, efficiency, reliability, maintainability and reusability (note: also security requirements) • Response time, throughput • Resource usage • Reliability, availability • Recovery from failure • Allowances for maintainability and enhancement • Allowances for reusability [1] Lethbridge and Laganière, Object Oriented Software Engineering: Practical Software Development using UML and Java, 2005
- 16. 16 Non-Functional Requirements (NFR) (2) • Design constraints: Categories constraining the environment and technology of the system. • Platform (minimal requirements, OS, devices…) • Technology to be used (language, DB, …) • Commercial constaints: Categories constraining the project plan and development methods • Development process (methodology) to be used • Cost and delivery date • Often put in contract or project plan instead
- 17. 17 Various NFR Types •Other ontologies also exist Performance requirements Space requirements Usability requirements Efficiency requirements Reliability requirements Portability requirements Interoperability requirements Ethical requirements Legislative requirements Implementation requirements Standards requirements Delivery requirements Safety requirements Privacy requirements Product requirements Organizational requirements External requirements Non-functional requirements Source: Gerald Kotonya and Ian Sommerville, Requirements Engineering – Processes and Techniques, Wiley, 1998
- 18. 18 Examples of Non-Functional Requirements •Product requirement • It shall be possible for all necessary communication between the APSE and the user to be expressed in the standard Ada character set. •Process requirement • The system development process and deliverable documents shall conform to the process and deliverables defined in XYZCoSPSTAN95. •Security requirement • The system shall not disclose any personal information about customers apart from their name and reference number to the operators of the system.
- 19. 19 Measurable Non-Functional Requirements Property Measure Speed Processed transactions/second User/Event response time Screen refresh time Size K Bytes Number of RAM 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 Source: Gerald Kotonya and Ian Sommerville, Requirements Engineering – Processes and Techniques, Wiley, 1998
- 20. 20 Goals •A Goal • Conveys the intention or the objective of one or many stakeholders • Can guide the discovery of verifiable non-functional requirements that can be tested objectively
- 21. 21 Example of Goal and NFR •A system goal • The system should be easy to use by experienced controllers and should be organized in such a way that user errors are minimized. •A verifiable usability requirement derived from this goal • Experienced controllers shall be able to use all the system functions after a total of three hours of training. • The average number of errors made by experienced controllers shall not exceed two per day. • Assumption: An experienced controller has at least 2 years experience with the old system (as stated by the stakeholder)
- 22. 22 Application-Domain Requirements •Derived from the application domain •Describe system characteristics and features that reflect the domain •May be new functional requirements, constraints on existing requirements, or define specific computations •If domain requirements are not satisfied, the system may be unworkable
- 23. 23 Examples of Application-Domain Requirements •Library system • The system interface to the database must comply with standard Z39.50. • Because of copyright restrictions, some documents must be deleted immediately on arrival. Depending on the user’s requirements, these documents will first be printed either locally or printed to a network printer and retrieved by the user. •Train protection system • The deceleration of the train shall be computed as: Dtrain = Dcontrol + Dgradient where Dgradient is 9.81ms2 * compensated gradient / alpha and where the values of 9.81ms2 / alpha are known for different types of train.
- 24. 24 Problems Concerning Application-Domain Requirements •Understandability • Requirements are expressed in the language of the application domain • This is often not understood by software engineers developing the system •Implicitness / Tacit knowledge • Domain specialists understand the area so well that they do not think of making the domain requirements explicit • People are often unaware of the tacit knowledge they possess and therefore cannot express it to others
- 25. 25 Emergent Properties (when the system consists of several sub-systems) •Properties of the system as a whole • Requirements which cannot be addressed by a single component, but which depend for their satisfaction on how all the software components interoperate • Only emerge once all individual subsystems have been integrated • Dependent on the system architecture •Examples of emergent properties • Reliability • Maintainability • Performance • Usability • Security • Safety
- 27. 27 Requirements within the software development process
- 28. 28 What is the right system to build ?
- 29. 29 Typical Layered Approach (V-shaped) Source: Hull, Jackson, Dick: Requirements Engineering, 2004
- 30. 30 Comments on previous slide Why combine RE with modeling ? •For analysis – models help to understand the problem domain •For documentation – models can be used for describing requirements (instead of solely using natural language)
- 31. 31 Back to the Sandwich – consider different levels of details Source: Hull, Jackson, Dick: Requirements Engineering, 2004
- 32. 32 Time Why? What? How? Who? When? If-Then Does It? Where? Project Management Process Quality Management Process Component & Configuration Management Process Risk Management Process Identify Business Needs and Goals Derive User & Functional Requirements Design Solutions TIME RE Process and Related Activities
- 33. 33 Requirements Engineering •Requirements engineering is a set of activities but not necessarily a separate phase Source: Donald C. Gause, Risk Focused Requirements Management, Tutorial at RE’09, September 2009
- 34. The Problem Domain and the System/Software-to-be
- 35. 35 Problem Domain •The problem domain is the context for requirements • Part of the world within which the problem exists • Needs to be understood for effective requirements engineering •Domain model • Set of properties assumed / believed to be true about the environment • Properties relevant to the problem • Problem domain requirements should hold in the proposed new version of the domain. •Define the system requirements such that: • If the system that is built satisfies the system requirements and the environment satisfies the properties assumed for the environment, then the problem domain requirements will be satisfied. • In simple words: The system will behave as required if the assumptions hold.
- 36. 36 Problem Domain and System-to-be A domain model should be reusable (Michael Jackson, 1995) Diagram also showing activities [Bray] Diagram showing existing and future situation [Lamsweerde] better: problem domain (as-is and to-be) Problem domain with system-to-be [Bray]
- 38. 38 Requirements Inception •Start the process • Identification of business need • New market opportunity • Great idea •Involves • Building a business case • Preliminary feasibility assessment • Preliminary definition of project scope •Stakeholders • Business managers, marketing people, product managers... •Examples of techniques • Brainstorming, Joint Application Development (JAD) meeting…
- 39. 39 Requirements Elicitation (1) •Gathering of information • About problem domain • About problems requiring a solution • About constraints related to the problem or solution •Questions that need to be answered • What is the system? • What are the goals of the system? • How is the work done now? • What are the problems? • How will the system solve these problems? • How will the system be used on a day-to-day basis? • Will performance issues or other constraints affect the way the solution is approached?
- 40. 40 Requirements Elicitation (2) •Overview of different sources • Customers and other stakeholders • Existing systems • Documentation • Domain experts • More ... •Overview of different techniques • Brainstorming • Interviews • Task observations • Use cases / scenarios • Prototyping • More ...
- 41. 41 Requirements Analysis •The process of studying and analyzing the needs of stakeholders (e.g., customer, user) in view of coming up with a “solution”. Such a solution may involve: • A new organization of the workflow in the company. • A new system (system-to-be, also called solution domain) which will be used in the existing or modified workflow. • A new software to be developed which is to run within the existing computer system or involving modified and/or additional hardware. •Objectives • Detect and resolve conflicts between requirements (e.g., through negotiation) • Discover the boundaries of the system / software and how it must interact with its environment • Elaborate system requirements to derive software requirements
- 42. 42 Requirements Specification •The invention and definition of the behavior of a new system (solution domain) such that it will produce the required effects in the problem domain •Requirements Analysis has defined the problem domain and the required effects •Specification Document • A document that clearly and precisely describes, each of the essential requirements (functions, performance, design constraints, and quality attributes) of the software and the external interfaces • Each requirement being defined in such a way that its achievement is capable of being objectively verified by a prescribed method (e.g., inspection, demonstration, analysis, or test) • Different guidelines and templates exist for requirements specification
- 43. 43 • Validation and verification • Both help ensure delivery of what the client wants • Need to be performed at every stage during the process • Validation: checks that the right product is being built (refers back to stakeholders – main concern during RE) • Verification: checks that the product is being built right • During design phase: refers back to the specification of the system or software requirements • During RE: mainly checking consistency between different requirements, detecting conflicts • Techniques used during RE • Simple checks • Formal Review • Logical analysis • Prototypes and enactments • Design of functional tests • Development of user manual Requirements Verification and Validation
- 44. 44 Requirements Management •Necessary to cope with changes to requirements •Requirements change is caused by: • Business process changes • Technology changes • Better understanding of the problem •Traceability is very important for effective requirements management Design document ....due to requirement 1.2 Requirements document 1.1 XXXX .... because 1.2 YYYY rationale Goals Elicitation notes
- 45. 45 Requirements Documents • Vision and Scope Document • Elicitation notes: (Raw) requirements obtained through elicitation; often unstructured, incomplete, and inconsistent • (Problem domain) Requirements document • System requirements document • Software requirements document • The software is normally part of a system that includes hardware and software. Therefore the software requirements are normally part of the system requirements. • Note: System and Software requirements may exist in several versions with different levels of details, such as • User (customer) requirements: Statements in natural language plus diagrams of the services the system provides and its operational constraints; written for customers • Detailed requirements: A structured document setting out detailed descriptions of the system services; often used as a contract between client and contractor. This description can serve as a basis for a design or implementation; used by developers.
- 46. 46 The Requirements Analyst1 •Plays an essential communication role • Talks to users: application domain • Talks to developers: technical domain • Translates user requirements into functional requirements and quality goals •Needs many capabilities • Interviewing and listening skills • Facilitation and interpersonal skills • Writing and modeling skills • Organizational ability •RE is more than just modeling… This is a social activity! [1] Karl Wiegers, In Search of Excellent Requirements
- 47. 47 For More Information a. B. A. Nuseibeh and S. M. Easterbrook, Requirements Engineering: A Roadmap. In A. C. W. Finkelstein (ed) The Future of Software Engineering, ACM Press, 2000 http://www.cs.toronto.edu/~sme/papers/2000/ICSE2000.pdf b. Simson Garfinkel, History's Worst Software Bugs, Wired News, 2005 http://www.wired.com/news/technology/bugs/0,2924,69355,00.html c. INCOSE Requirements Working Group http://www.incose.org/practice/techactivities/wg/rqmts/ d. Tools Survey: Requirements Management (RM) Tools http://www.incose.org/productspubs/products/rmsurvey.aspx http://www.volere.co.uk/tools.htm e. IEEE (1993) Recommended Practice for Software Requirements Specifications. IEEE Std 830-1993, NY, USA. f. IEEE (1995) Guide for Developing System Requirements Specifications. IEEE Std P1233/D3, NY, USA. g. Requirements Engineering Conference http://www.requirements-engineering.org/
- 48. 48 Main References a. Jeremy Dick, Elizabeth Hull, Ken Jackson: Requirements Engineering, Springer-Verlag, 2004 b. Soren Lauesen: Software Requirements - Styles and Techniques, Addison Wesley, 2002 c. Ian K. Bray: An Introduction to Requirements Engineering, Addison Wesley, 2002 d. Karl E. Wiegers: Software Requirements, Microsoft Press, 2003 e. Gerald Kotonya, Ian Sommerville: Requirements Engineering – Processes and Techniques, Wiley, 1998 f. Roger S. Pressman: Software Engineering – A Practitioner's Approach, McGraw-Hill, 2005 g. Tim Lethbridge, Robert Laganière: Object Oriented Software Engineering: Practical Software Developement using UML and Java, 2nd edition, McGraw-Hill, 2005 h. Ivy F. Hooks, Kristin A. Farry: Customer-Centered Products – Creating Successful Products Through Smart Requirements Management, Amacom, 2001 i. CHAOS Report, Standish Group