[T Shioda :Mordell-Weil lattice][1]
[1]: T Shioda :Mordell-Weil latticehttp://www.rkmath.rikkyo.ac.jp/math/shioda/papers/mwl.pdf more Basic,you also see the homepage of Chao Li about Elliptic Surfaces and Mordell-Weil Lattices in harvard university。