December 2008
Beginner
320 pages
8h 52m
English
Content preview from Requirements Modelling and Specification for Service Oriented Architecture
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3.3. Problem Frames
A more profound approach is due to Jackson (1995, 2001). He defines a problem frame as a structure consisting of principal parts and a solution task. The principal parts correspond to what we have met as actors, use cases and business objects, along with other actions and goal-oriented conversations. The solution task is the work one has to do to meet some requirement concerning these parts or objects. He then abstracts from the objects to problem domains and the phenomena that are shared between them: in the sense of the elements that can be described in the languages of both domains.
In Figure 3-5, the rectangles represent problem domains and the connecting lines shared phenomena: shared events, states and values. These are sometimes labelled and expanded, so that the connector labelled 's' lets the machine read off inter alia the safe ranges for the sensors attached to a patient's body. The annotation PMS indicates that it is the machine that initiates any alarms. Rectangles with a double vertical line represent machine domains - one per frame and those with a single represent domain that must be designed - as opposed to being part of the uncontrollable world.
Figure 3.5. A problem context diagram.
Figure 3.6. A problem diagram (after Jackson, 2001).
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