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Scenario-Based Requirements Modeling: Definition & Application

Instructor: Alexis Kypridemos

Alexis is a technical writer for an IT company and has worked in publishing as a writer, editor and web designer. He has a BA in Communication.

Scenario-based modeling is defined and explained within the greater context of requirements modeling for software engineering. Use case and activity diagrams are also explained using examples.

What is Scenario-Based Requirements Modeling?

To understand scenario-based modeling, you first need to understand requirements modeling and how it applies to software engineering in general. Requirements modeling is essentially the planning stage of a software system or application. The path by which such a system or application comes to life will generally begin with a business or entity identifying a problem they're facing that requires a software solution, and they approach a software development team to come up with this solution. Requirements modeling is the process of identifying the requirements this software solution must meet in order to be successful. Requirements modeling contains several sub-stages, typically: scenario-based modeling, flow-oriented modeling, data modeling, class-based modeling and behavioral modeling. Also, as the term 'modeling' implies, all of these stages typically result in producing diagrams that visually convey the concepts they identify. The most common method for creating these diagrams is UML, Unified Modeling Language.

What Does Scenario-Based Modeling Do?

While technically there is no 'right way' to go through the stages of requirements modeling, it typically begins with scenario-based modeling, and that is because it identifies the possible use cases for the system and produces the use case diagram, to which all the other stages of requirements modeling refer.

Use Case

The use case is essentially a primary example of how the proposed software application or system is meant to be used, from the user's point of view. A use case diagram will typically show system 'actors' (humans or other entities external to the system) and how they interact with the system. Technically, each action such a system actor can perform with the application or system is considered to be a separate use case.

Use Case Diagram

The example use case diagram above, drawn using UML, depicts three possible use cases for the system actor 'Traveler' when interacting with an airline company's application. The three use cases / actions depicted are:

  1. Search for flights
  2. Buy tickets
  3. Get boarding pass

The large rectangle labeled 'Airline Company Application' represents the system boundary. Notice that the actor labeled 'Traveler' is outside the system boundary. In UML, all actors are depicted outside the system boundary.

Activity Diagram

In addition to the use case diagram, scenario-based modeling can also produce an activity diagram, which is essentially a more advanced flow chart that depicts how one activity leads to another while using a system.

Activity Diagram

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