An information source alignment system may include 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. The source and target category hierarchy trees may be constructed from a class hierarchy of a knowledge source. A class-similarity determination module may compare the source and target category hierarchy trees. An alignment module may determine whether the source and target classes are aligned based on the comparison of the source and target category hierarchy trees.