TIMESTAMP SEMANTICS AND REPRESENTATION

Many database management systems and operating systems provide support for time values. At the physical level time values are known as times tamps. A timestamp has a physical realization and a temporal interpret ation. The physical realization is a pattern of bits while the tempora l 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 defin itions of this fundamental time unit. We propose a more precise tempor al interpretation, the time-line clock, that constructs a time-line by using different well-defined clocks in different periods. We also pro pose timestamp formats for events, intervals and spans. These formats can represent all of time to the granularity of a second, and all of r ecorded history to a finer granularity of a microsecond. Our proposed formats were designed to be more space and time efficient than existin g representations. We compare our formats with those used in common op erating systems and database management systems.