6. software requirements
- 2. INTRODUCTION Requirements form the basis for all software products Requirements engineering is the process, which enables us to systematically determine the requirements for a software product
- 3. SOFTWARE REQUIREMENT-1 A complete description of what the software system will do without describing how it will do it is represented by the software requirements
- 4. SOFTWARE REQUIREMENT-2 Software requirements are complete specification of the desired external behavior of the software system to be built They also represent External behavior of the system
- 5. IEEE DEFINITION A condition or ability that must be met or possessed by a system...to satisfy a contract, standard, specification, or other formally imposed document IEEE Std 729
- 6. SOURCE OF REQUIREMENT Stakeholders People affected in some way by the system Documents Existing system Domain/business area
- 7. EXAMPLE OF REQUIREMENT-1 The system shall maintain records of all payments made to employees on accounts of salaries, bonuses, travel/daily allowances, medical allowances, etc.
- 8. EXAMPLE OF REQUIREMENT-2 The system shall maintain records of all library materials including books, serials, newspapers and magazines, video and audio tapes, reports, collections of transparencies, CD-ROMs, DVDs, etc.
- 9. EXAMPLE OF REQUIREMENT-3 The system shall allow users to search for an item by title, author, or by International Standard Book Number The system’s user interface shall be implemented using a web browser
- 10. KINDS OF SOFTWARE REQUIREMENTS Functional requirements Non-functional requirements Domain requirements Inverse requirements Design and implementation constraints
- 12. FUNCTIONAL REQUIREMENT-1 Statements describing what the system does Functionality of the system
- 13. FUNCTIONAL REQUIREMENT-2 Statements of services the system should provide Reaction to particular inputs Behavior in particular situations Functional requirements are the backbone of all software products
- 14. FUNCTIONAL REQUIREMENT-3 Functional requirements should be complete and consistent Customers and developers usually focus all their attention on functional requirements
- 15. FUNCTIONAL REQUIREMENT EXAMPLE The system shall solve a quadratic equation using the following formula x = (-b+sqrt(b2 – 4*a*c))/2*a
- 16. FUNCTIONAL REQUIREMENT EXAMPLE The user shall be able to search either the entire database of patients or select a subset from it (admitted patients, or patients with asthma, etc.)
- 17. FUNCTIONAL REQUIREMENT EXAMPLE Every order shall be allocated a unique identifier (ORDER_ID) which the user shall use to access that order
- 19. NON-FUNCTIONAL REQUIREMENT Most non-functional requirements relate to the system as a whole. They include constraints on timing, performance, reliability, security, maintainability, accuracy, the development process, standards, etc.
- 20. NON-FUNCTIONAL REQUIREMENT Must be built into the framework of the software product Failure to meet a non-functional system requirement may make the whole system unusable
- 21. EXAMPLE For example, if an aircraft system does not meet reliability requirements, it will not be certified as ‘safe’ If a real-time control system fails to meet its performance requirements, the control functions will not operate correctly
- 22. NON-FUNCTIONAL REQUIREMENT Non-functional requirements arise through user needs, budget constraints, organizational policies, interoperability with other software and hardware systems, external factors like safety regulations, privacy legislation, etc.
- 25. PRODUCT REQUIREMENT EXAMPLE The system shall allow one hundred thousand hits per minute on the website The system shall not have down time of more than one second for continuous execution of one thousand hours
- 27. ORGAN. REQUIREMENT EXAMPLE The system development process and deliverable documents shall conform to the MIL-STD-2167A Any development work sub-contracted by the development organization shall be carried out in accordance with Capability Maturity Model
- 29. EXTERNAL REQUIREMENT EXAMPLE The system shall not disclose any personal information about members of the library system to other members except system administrators The system shall comply with the local and national laws regarding the use of software tools
- 30. OBSERVATION ON NFR Non-functional requirements can be written to reflect general goals for the system. Examples include: Ease of use Recovery from failure Rapid user response
- 31. OBSERVATION ON NFR oObjective verification is difficult oDistinction between functional and non- functional is not always very clear
- 32. CONT. Non-functional requirements should be written in a quantitative manner as much as possible, which is not always easy for customers For some goals, there are no quantitative measures, e.g., maintainability
- 33. CONT. Goals can be useful to designers and developers, as they give clues to them about priorities of the customers Non-functional requirements should be highlighted in the requirements document, so that they can be used to build the architecture of the software product
- 34. SUMMARY Introduction Software Requirement Definition Functional Requirement with example NFR Product Requirement Organizational Requirement External Requirement Observation on NFR