1. An information source alignment system comprising: a tree generation module executed by a computer system to generate a source category hierarchy tree for a source class in a first information source and a target category hierarchy tree for a target class in a second information source, wherein the source and target category hierarchy trees are constructed from a class hierarchy of a knowledge source; a class-similarity determination module comparing the source and target category hierarchy trees; and an alignment module determining whether the source and target classes are aligned based on the comparison of the source and target category hierarchy trees.