  Data Integration of heterogeneous data sources relies either on periodically
transferring large amounts of data to a physical Data Warehouse or retrieving
data from the sources on request only. The latter results in the creation of
what is referred to as a virtual Data Warehouse, which is preferable when the
use of the latest data is paramount. However, the downside is that it adds
network traffic and suffers from performance degradation when the amount of
data is high. In this paper, we propose the use of a readCheck validator to
ensure the timeliness of the queried data and reduced data traffic. It is
further shown that the readCheck allows transactions to update data in the data
sources obeying full Atomicity, Consistency, Isolation, and Durability (ACID)
properties.
