In string compactifications, frequently there appears the anomalous U(1) gauge symmetry which belonged to E8$times$E8 of the heterotic string. This anomalous U(1) gauge boson obtains mass at the compactification scale, just below $10^{18,}$GeV, by absorbing one pseudoscalar (corresponding to the model-independent axion) from the second rank anti-symmetric tensor field $B_{MN}$. Below the compactification scale, there results a global symmetry U(1)$_{rm anom}$ whose charge $Q_{rm anom}$ is the original gauge U(1) charge. This is the most natural global symmetry, realizing the invisible axion. This global symmetry U(1)$_{rm anom}$ is suitable for a flavor symmetry. In the simplest compactification model with the flipped SU(5) grand unification, we calculate all the low energy parameters in terms of the vacuum expectation values of the standard model singlets.
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