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Full-Text Articles in Physical Sciences and Mathematics
Parametricity And Local Variables, Peter W. O'Hearn, R. D. Tennent
Parametricity And Local Variables, Peter W. O'Hearn, R. D. Tennent
Electrical Engineering and Computer Science - Technical Reports
We propose that the phenomenon of local state may be understood in terms of Strachey's concept of parametric (i.e., uniform) polymorphism. The intuitive basis for our proposal is the following analogy: a non-local procedure is independent of locally-declared variables in the same way that a parametrically polymorphic function is independent of types to which it is instantiated. A connection between parametricity and representational abstraction was first suggested by J. C. Reynolds. Reynolds used logical relations to formalize this connection in languages with type variables and user-defined types. We use relational parametricity to construct a model for an Algol-like language in …
Timestamp Semantics And Representation., Curtis Dyreson, Richard T. Snodgrass
Timestamp Semantics And Representation., Curtis Dyreson, Richard T. Snodgrass
Curtis Dyreson
Many database Management systems and operating systems provide support for time values. At the physical level time values are known as timestamps. A timestamp has a physical realization and a temporal interpretation. The physical realization is a pattern of bits while the temporal interpretation is the meaning of each bit pattern, that is, the time each pattern represents. All previous proposals defined timestamps in terms of seconds. However, as we show, there are at least seven definitions of this fundamental time unit. We propose a more precise temporal interpretation, the time-line clock, that constructs a time-line by using different well-defined …