  The concept of system signature was introduced by Samaniego for systems whose
components have i.i.d. lifetimes. We consider its extension to the continuous
dependent case and give an explicit expression for this extension as a
difference of weighted means of the structure function values. We then derive a
formula for the computation of the coefficients of these weighted means in the
special case of independent continuous lifetimes. Finally, we interpret this
extended concept of signature through a natural least squares approximation
problem.
