From harmoni

The Harmoni DataManager was originally conceived as a storage service that would allow applications to create multiple data-schemas (structures of data) and store data-records for those schemas all on the fly, without adding or changing database tables. The DataManager does all of this, but can be quite a challenge to work with and is not a service that most developers would want to try using unless it precisely fits their needs.

The current Harmoni Repository OSID implementation makes use of the DataManager for storing RecordStructures and Records, and marries this with the Hierarchy in order to provide hierarchical arrangements of Repositories and Assets.

The Repository OSID is the preferred API to use for data storage. The DataManager will live on in Harmoni until the Repository OSID implementation is refactored to use an improved data-storage system. At that point it will likely be retired.