c 55 d2

 “Obstacle Diagrams and Obstacle Identification” Please respond to the following:

From the e-Activity, determine any similarities or dissimilarities between the goal model diagrams and obstacles diagrams.
Provide one example of when you would use the tautology-based refinement technique. Provide one example of when you would use the obstructed target technique. Defend why you chose to use each technique in the examples that you did.

 
From the e-Activity, determine any similarities or dissimilarities between the goal model diagrams and obstacles diagrams.
Fig. 1 Similarities & Dissimilarities between Goal & Obstacle Model Diagrams
Goal Model Diagram
Obstacle Model Diagram
Similarities

Can be refined into lower-level leaf nodes
Uses AND and OR nodes
Can be refined into lower-level leaf nodes
Uses AND and OR nodes

Dissimilarities

Is refined from the top-down
Is refined from the bottom-up

Figure 1 presents similarities and dissimilarities between goal model and obstacle model diagrams. Based on the video, both diagrams can contain AND or OR nodes.  In addition, both can be refined into lower-level leaf nodes.  When goals and obstacles are refined into leaf nodes, they are at their most basic level.
Goal model diagrams and obstacle model diagrams are dissimilar in the way they are refined. Goal model diagrams are refined from the top-down. Obstacle model diagrams are fined from the bottom-up.
Provide one example of when you would use the tautology-based refinement technique. Provide one example of when you would use the obstructed target technique. Defend why you chose to use each technique in the examples that you did.
Tautology-based refinement and obstructed target refinement are two obstacle refinement techniques. Tautology-based refinement refines parent obstacles into lower-level obstacles by altering the AND or OR in the condition.  For example, not (A or B) becomes not A or B (Lamsweerde, 2009).  This technique would be used in a situation where the obstacle of either one goal or the other needs to be found.  Using the train example in the book, the tautology-based refinement can be used to find the obstacle of either one of the goals: arriving into the next station on time and stopping safely (Lamsweerde, 2009). Such a technique used in this situation is important because requirement engineers (REs) often need to find the obstacle that would prevent one of two goals from occuring.
The obstructed target technique is the process of finding the obstacle that would prevent a particular goal from being achieved (Lamsweerde, 2009).  Using the train example again, the obstructed target technique can be used to determine what obstacle would prevent the train from stopping safely.  For example, if block signal set to stop, then arriving train stops.  In order to find the obstacle, the obstructed target technique can be used to ask the question “what would prevent the train from stopping at the signal?”  This would allow the RE to determine what factors would cause the train not to stop (Lamsweerde, 2009). This technique is important because REs often need to find one or more obstacles that would prevent a particular target condition (i.e. goal).
References
Lamsweerde, A. V. (2009). Requirements Engineering: From System Goals to UML Models to Software Specifications. Chichester, West Sussex, England: John Wiley & Sons, Ltd. Retrieved April 29, 2018, from https://strayer.vitalsource.com/#/books/978EUDTE00270/