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- 1. Software Engineering CS-1251 UNIVERSITY OF SIALKOT Topic: Requirement Engineering
- 2. Recommended Books Ian, S. 2016. Software Engineering. 10th Ed. Addison Wesley, Boston, MA, USA. Gary, B. S., T. J, Cashman and H. J. Rosenblatt. 2017. Systems Analysis and Design. 9th Ed. Cengage Learning, Boston, MA, USA. Roger, S.P. 2016. Software Engineering: A Practitioner's Approach. 8th Ed. McGraw- Hill.Beijing, China.
- 3. Content to complete Functional Requirements Non-Functional Requirements
- 4. Requirements Engineering The process of establishing the services that the customer requires from a system and the constraints under which it operates and is developed. The requirements themselves are the descriptions of the system services and constraints that are generated during the requirements engineering process. 4
- 5. 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. 5
- 6. 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 what should be implemented so may be part of a contract between client and contractor. 6
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- 8. Readers of different types of requirements specification 8
- 9. Functional and Non-Functional Requirements Functional requirements – Statements of services the system should provide, how the system should react to particular inputs and 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, etc. – Often apply to the system as a whole rather than individual features or services. – How The System Performs A Certain Function 9
- 10. Functional requirements •Describe functionality or system services. •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. •Functional system requirements should describe the system services in detail. 10
- 11. Functional Requirements (cont..) Some of the more typical functional requirements include Organization Rules Administrative functions Authentication Authorization levels 11
- 12. Functional 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. 12
- 13. 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. 13
- 14. Non-Functional Requirements Some typical non functional requirements are: Performance(Response time) Security Maintainability Availability Dependability Capacity 14
- 15. 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. 15
- 16. 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 16 Metrics for specifying non- Functional Requirements
- 17. Differences between Functional and Non Functional Requirements Functional Non Functional A functional requirement defines a system or its component. A non-functional requirement defines the quality attribute of a software system. It specifies “What should the software system do?” It places constraints on “How should the software system fulfill the functional requirements?” Functional requirement is specified by User. Non-functional requirement is specified by technical peoples e.g. Architect, Technical leaders and software developers. It is mandatory. It is not mandatory. 17
- 18. Differences between Functional and Non Functional Requirements Functional Non Functional It is captured in use case. It is captured as a quality attribute. Defined at a component level. Applied to a system as a whole. Helps you verify the functionality of the software. Helps you to verify the performance of the software. Functional Testing like System, Integration, End to End, API testing, etc are done. Non-Functional Testing like Performance, Stress, Usability, Security testing, etc are done. 18
- 19. Functional and Non-Functional Requirements Example Functional Non Functional 1) Authentication of user whenever he/she logs into the system. 1) Emails should be sent with a latency of no greater than 12 hours from such an activity. 2) System shutdown in case of a cyber attack. 2) The processing of each request should be done within 10 seconds 3) A Verification email is sent to user whenever he/she registers for the first time on some software system. 3) The site should load in 3 seconds when the number of simultaneous users are > 10000
- 20. Functional and Non-Functional Requirements Example