This thesis proposes a safety-oriented variant of Statecharts, called Safecharts, . devoted exclusively for safety-critical systems design. Safecharts maintains two separate representations for functional and safety requirements, bringing the distinctions and dependencies between such :tequirements into sharper focus. A fundamental concept of Safecharts, on which many of its features are based, is an explicit ordering of system states according to the risks posed by them. Mathematically, this takes the form of a risk ordering relation. Recognising the possibility of gaps and inaccuracies in the definition of such a relation (for example, due to human error or the lack of knowledge) , Safecharts imposes an additional clustering of states into what is referred to as risk bands and constructs a risk graph of these states. Based on the above, Safecharts incorporates ways to represent various safety requirements of the system, equipment failures and'failure handli.n. g mechanisms. Safecharts classifies transitions according to their risk natur&'into safe, unsafe and neutraL It also extends their labelling to call for additional safeguards against unsafe transitions and prompt enforcement of safe ones. Relying on the concept of risk distance of transitions, Safecharts provides a safety-oriented scheme for resolving any unpredictable nondeterministic patterns of behaviour. The thesis clarifies the above concepts using illustrations and precise mathematical definitions.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:485389 |
| Date | January 2005 |
| Creators | Dammag, Hamdan Zaid |
| Publisher | University of Reading |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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