1. A versioned relational database system, a processor and storage apparatus accessible to the processor being used to implement the versioned relational database system and the versioned relational database system comprising: a source of a plurality of versions of data; a plurality of workspaces, each workspace giving access to a version of the data; and metadata that specifies relationships among the workspaces such that a workspace is a node in a graph which permits workspace to have more than one parent workspace, wherein the processor performs operations on the versions of the data in the workspaces, the manner of performance of an operation being determined at least in part by the metadata.