Requirements Modelling:Scenario based models software Engineering ___ Notes Scenario-Based Modeling (1) What should we write about? (2) How much should we write about it? (3) How detailed should we make our description? (4) How should we organize the description? What to Write About? ● Inception and elicitation—provide you with the information you’ll need to begin writing use cases. ● Requirements gathering meetings, QFD, and other requirements engineering mechanisms are used to ○ ○ ○ ○ ○ identify stakeholders –define the scope of the problem –specify overall operational goals –establish priorities –outline all known functional requirements, and ○ –describe the things (objects) that will be manipulated by the system. ● To begin developing a set of use cases, list the functions or activities performed by a specific actor How Much to Write About? ● As further conversations with the stakeholders progress, the requirements gathering team develops use cases for each of the functions noted. ● In general, use cases are written first in an informal narrative fashion. ● If more formality is required, the same use case is rewritten using a structured format similar to the one proposed. Use-Cases ● a scenario that describes a “thread of usage” for a system ● actors represent roles people or devices play as the system functions ● users can play a number of different roles for a given scenario Developing a Use-Case ● ● ● ● ● What are the main tasks or functions that are performed by the actor? What system information will the actor acquire, produce or change? Will the actor have to inform the system about changes in the external environment? What information does the actor desire from the system? Does the actor wish to be informed about unexpected changes? SCENARIOS ● Scenario is another name for a particular flow of events. ● A use case covers a range of situations – a scenario is just one. ● Each use case typically has: ○ a main flow describing the “happy path” ○ alternate flows describing major exceptions ● Several alternatives exist for