A common limitation of all the existing nested transaction models is that they only allow subtransactions to commit either to parent transactions or to databases. In order to adequately balance atomicity and concurrency at selected levels of a transaction hierarchy, the notion of scoped commitment is proposed, that allows a subtransaction to commit to a selected ancestor independently of its parent, making its results visible to that ancestor and thus improving the concurrency in the transaction subtree beneath that ancestor. A corresponding scoped undo approach is also developed that allows a transaction hierarchy with subtransactions having mixed commit scopes to partially and consistently roll back upon failure, then restart and roll forward.