Software architecture3
- 1. Software Architecture & Design By Syed Salman Qadri Assistant Professor (CS) The Islamia University of Bahawalpur 1
- 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 2
- 3. Importance of Software Requirements • The hardest single part of building a software system is deciding what to build...No other part of the work so cripples the resulting system if done wrong. No other part is difficult to rectify later – Fred Brooks 3
- 4. Examples of Requirements • The system shall maintain records of all payments made to employees on accounts of salaries, bonuses, travel/daily allowances, medical allowances, etc. 4
- 5. Examples of Requirements • The system shall interface with the central computer to send daily sales and inventory data from every retail store 5
- 6. Examples of Requirements • 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. 6
- 7. Examples of Requirements • 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 7
- 8. Examples of Requirements • The system shall support at least twenty transactions per second • The system facilities which are available to public users shall be demonstrable in ten minutes or less 8
- 9. Kinds of Software Requirements 9
- 10. Kinds of Software Requirements • Functional requirements • Non-functional requirements • Domain requirements • Inverse requirements • Design and implementation constraints 10
- 11. Functional Requirements 11
- 12. Functional Requirements • Statements describing what the system does. • Functionality of the system 12
- 13. Functional Requirements • Statements of services the system should provide – Reaction to particular inputs – Behavior in particular situations 13
- 14. Functional Requirements • Sequencing and parallelism are also captured by functional requirements • Abnormal behavior is also documented as functional requirements in the form of exception handling 14
- 15. Functional Requirements • Functional requirements should be complete and consistent • Customers and developers usually focus all their attention on functional requirements 15
- 16. Functional Requirements Example • The system shall solve a quadratic equation using the following formula x = (-b+sqrt(b2 – 4*a*c))/2*a 16
- 17. Functional Requirements 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
- 18. Functional Requirements Example • The system shall provide appropriate viewers for the user to read documents in the document store 18
- 19. Functional Requirements Example • Every order shall be allocated a unique identifier (ORDER_ID) which the user shall use to access that order 19
- 20. Functional Requirements Example • The system shall allow customers to return non-perishable items within fifteen days of the purchase. A customer must present the original sale receipt to return an item 20
- 21. Comments on Examples • Notice the level of detail in different requirements described above. Some are very detailed compared to others 21
- 22. Comments on Examples • Notice the ambiguity in the requirement, which uses the term ‘appropriate viewers’ • This requirement does not mention the formats of documents and types of viewers, which can be used 22
- 23. Comments on Examples • Notice the ambiguity in the requirement for solving the quadratic equation. The requirement does not speak about the possibility when the value of ‘a’ is zero x = (-b+sqrt(b2 – 4*a*c))/2*a 23
- 24. Comments on Examples • Incomplete and ambiguous requirements are open to multiple interpretations and assumptions • This can lead to the development of poor quality, or faulty, software products 24
- 25. Summary • Requirements form the basis of all software engineering projects • Functional requirements capture the behavioral aspects/functions of the proposed automated system • Functional requirements are the backbone of all software products 25
- 26. References • ‘Requirements Engineering: Processes and Techniques’ by G. Kotonya and I. Sommerville, John Wiley & Sons, 1998 • Software Requirements: Objects, Functions, and States by A. Davis, PH, 1993 • Software Engineering 8th Edition, by I. Sommerville, 2008 • Software Engineering 5th Edition, by R. Pressman 26