Abstract: A method and system for interfacing an application program with a compound document storage system. The present invention provides an interface which an application program uses to manipulate compound documents. In a preferred embodiment, this interface is implemented in a multilayered architecture. The first layer provides methods which an application program uses to access a compound document using the functions of the second layer. The second layer maps requests to store data in the compound document to a storage format using the functions of the third layer. The third layer maps requests to write to a file to an arbitrary storage medium. In another aspect, the present invention provides for the transactioning of modifications to data in a file that is stored in a tree structure having nodes. When modifications are made to a node that is not transacted, the modifications are associated with the closest ancestor node that is transacted.