Abstract text

A version history of each of a plurality of resources is stored in a table. The version history for each resource comprises a set of one or more values for the resource, wherein each value in the version history of a resource indicates the value that the resource had in a particular version of the resource. In response to a request to perform an operation that causes a given resource that is subject to a uniqueness constraint to have a particular value, it is determined whether the uniqueness constraint is violated based on whether any version of any resource other than the given resource has the particular value. The uniqueness constraint is determined to be violated if any version of any resource other than the given resource has the particular value. The uniqueness constraint is not violated by existence of a version of the given resource that has the particular value.