Roxana - Gabriela HORINCAR Refresh Strategies and Online ... - LIP6

items with the publication frequency of λ = 10 items/hour, an aggregator that refreshes
that source less than once an hour r = 1 will lose items, as the source becomes saturated
before being refreshed.
Definition 2.1.7. Saturation coefficient
Given the publication window size Ws, the publication frequency λ and the refresh rate r
of the source s, we define the saturation coefficient SatCoeff(n, s) ∈ [0, 1] of source s in
relation with aggregator n as the percentage of items published by s and lost by n:
�
Ws·r
1 −
SatCoeff(n, s) =
λ if Ws · r < λ
0 otherwise
As an example, given that the value of the publication window size is fixed to Ws = 10, the
graph of the saturation coefficient is presented in Figure 2.3 as a function of the publication
frequency λ and refresh rate r.
Figure 2.3: Saturation coefficient
In case the publication behavior of the sources varies in time (the publication frequency
λ(t) �= const), which is always the case in real world, the description done by the saturation
coefficient is only an approximate one, useful for well understanding the saturation process.
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