Here, results are produced only when an exceptional condition is reached (the temperature is outside the desired range), and thus relatively few tuples will match. We note that this is a low selectivity query, indicating that it outputs (selects) a small percentage of the original sensor tuples. As mentioned above, our discussions with engineers in industrial settings suggest that each sensor may have sev- eral alarm conditions associated with it, and there may be hundreds or thousands of sensors in a single factory. In a typical deployment such as Intel’s, there could be several thousand filters, each.
