I am currently reading a couple of papers about event processing. In the context of ordering events, "2g-precedence" is frequently mentioned. I don't know what it is, and I cannot find much information about it. In this paper I was able to find a short explanation that is way over my head, though:
[It is assumed] that the maximum time difference between any two clocks at the same instant of time is bounded by $\delta$. The granularity condition states that the granularity of the global time-base $g$ should not be smaller than $\delta$, $g > \delta$, ensuring that global clocks do not overlap. A global and total order of events can be determined if event timestamps are two or more clock ticks apart, a fact known as 2g-precedence. If this assumption does not hold in all cases, one has to face partial ordering of events.
What is a "granularity condition"? What is a "global time-base"? How do clocks "overlap"? In other words, what is "2g-precedence"?