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Section 8.10.1.2:
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This abstract class defines a state component which is a set of all instantiations of objects of any class sub-typing from this class in addition to the vdm model types used wherever this class name is used. Note that SAME has to be an instantiated class, not an abstract one.
types SAME = object_type ; $OUT_DEVICE = set of object_type state multi : $OUT_DEVICE inv multi_types == forall obj in set multi_types & sub_type($OUT_DEVICE,obj)
NOTE | See the important note about vdm state in the notes on vdm-sl usage in this specification. |
This abstraction models a device which, at least potentially, has the ability to send data to some external device.
This feature provides an enquiry facility for a program to determine whether output is currently possible from the instantiated class device.
output_possible(self : SAME) res : BOOL
Since this feature is a predicate, the pre-condition is vacuously true.
The result reflects the state of the real device being modelled by the instantiating class. The post-condition, however, is vacuously true.
This predicate returns true if and only if the device is in a state where data can be exported by the program.
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or enquiries should be made toKeith Hopper. Page last modified: Wednesday, 4 April 2001. |
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