Figure 6 2 goal model in the form of an andor tree

This preview shows page 82 - 85 out of 182 pages.

Figure 6-2 Goal model in the form of an AND/OR tree Easy-to-use Well-equipped
Image of page 82

Subscribe to view the full document.

64 6 Model-Based Requirements Documentation Modeling goals with AND/OR trees As the goal model in figure 6-2 shows, the goal “comfortable navigation to destination” is refined into the three sub-goals “dynamic route calculation with respect to traffic congestion”, “comfortable destination input”, and “comfortable route guidance” via AND-decomposition. This depicts that all three sub-goals must be met to consider the super-goal fulfilled. The sub-goal “dynamic route calculation with respect to traffic congestion” in turn is refined by the two sub-goals “manual input of traffic conditions” and “automatic update of traffic data”. The type of decomposition relation depicts that only one of the two sub-goals must be met to consider the super-goal met. 6.3 Use Cases Use cases were first proposed in [Jacobson et al. 1992] as a method to document the functionalities of a planned or existing system on the basis of simple models. The use case approach is based on two concepts that are used in conjunction with one another: Use case diagrams Use case specifications 6.3.1 UML Use Case Diagrams Relations between use cases Use case diagrams in the UML [OMG 2007] (see section 4.2.3 ) are simple models to schematically document the functions of a system from a user’s perspective and to document the interrelations of the functions of a system and the relations between these functions and their environment. Modeling Elements of UML Use Case Diagrams Figure 6-3 shows the most essential modeling elements of use case diagrams, as defined in the Unified Modeling Language (UML) [OMG 2007] .
Image of page 83
6.3 Use Cases 65 Figure 6-3 Essential modeling elements of use case diagrams n Use cases: Uses cases that are defined for the system are depicted using oval shapes. These shapes contain the name of the use case. Alternatively, the name can be written beneath the use case. o Actors: Actors are outside the system boundary and represent people or systems that interact with the system modeled. Actors are depicted by a rectangle that receives the name of the actor and is tagged with the stereotype “actor”. If the actor is a person, a stick figure may be used. If the actor is a system, either a rectangle or a stick figure may be used in conjunction with the stereotype “system”. p System boundaries: System boundaries within a use case diagram separate the parts of the use case that are part of the system from the parts (people or systems) that are outside the system boundary. Optionally, the name of the system may be denoted at the system boundary in the diagram. q Extend relation: An extend relation depicts that an interaction sequence that belongs to use case A extends some interaction sequence in use case B at a specified point. This is known as the extension point. The extension is triggered by the condition defined.
Image of page 84

Subscribe to view the full document.

Image of page 85

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Ask Expert Tutors You can ask 0 bonus questions You can ask 0 questions (0 expire soon) You can ask 0 questions (will expire )
Answers in as fast as 15 minutes