Whether it is for audit or for recovery purposes, data checkpointing is an important problem of distributed database systems. Actually, transactions establish dependence relations on data checkpoints taken by data object managers. So, given an arbitrary set of data checkpoints (including at least a single data checkpoint from a data manager, and at most a data checkpoint from each data manager), an important question is the following one: ``Can these data checkpoints be members of a same consistent global checkpoint?''. This paper answers this question by providing a necessary and sufficient condition suited for database systems. Moreover, to show the usefulness of this condition, two {\em non-intrusive} data checkpointing protocols are derived from this condition. It is also interesting to note that this paper, by exhibiting ``correspondences'', establishes a bridge between the data object/transaction model and the process/message-passing model.