7M822 Software Requirements A Use Case Approach 14 September 2010

7M822 Software Requirements The Rock Problem ?! [Ed Yourdon] 2

7M822 Software systems nature Software systems by their nature are –intangible –abstract –complex –infinitely changeable 3

7M822 Requirements engineering Get a complete description of the problem –feasibility study 4

7M822 Software development Goal –to develop quality software that meets customers’ needs What is this software supposed to do? How, exactly, will we know when the software does exactly that and nothing else? 5

7M822 Software requirement A software requirement is a capability needed by the user to solve a problem to achieve an objective, and is imposed on the system 6

7M822 Problem domain The problem domain is the home of those people (real users, other stakeholders) whose needs must be addressed in order to build the perfect system. 7

7M822 Needs Features Software requirements problem domain solution domain 8

7M822 Stage Relative cost to repair a defect Derived from: Alan Davis, Software Requirements: objects,functions and states; Prentice-Hall, 1993 Requirements time Design Coding Unit test Acceptance test Maintenance

7M822 Functional requirements Find the solution for the user needs by proposing objectives for the system that involves –problem definition –identifying the users –defining the solution system boundary –identifying the constraints 10

7M822 Defining solutions system boundary System InputsOutputs inputs / system / outputs relationship Of concern: 1.Our system 2.Things that interact with our system actor 11

7M822 System boundary Our Solution Users Other Systems System Boundary I/O 12

7M822 System perspective New Solution Users Catalog system System Boundary Library system 13

7M822 Use case approach Lending services User administration Books database Library user Library staff library system 14

7M822 NS Ticket machine – a use case approach Traveler Purchase Ticket Maintenance basic data NS Take ticket Destination 15

7M822 Example Use Cases A simple word processor is required to create new and edit existing documents. Also the ability to print is required. Question? Find the system boundary, actors and use cases 16

7M822 Study matter Ian Sommerville Software Engineering, 6 th edition – Ch.6 Addison Wesley Dean Leffingwell & Don Widrig Managing Software Requirements, 2 nd edition Addison Wesley 17