Time Series Data Validity

As a key step of data preparation, it is always necessary to first assert the quality of data before conducting any data application. Given a set of constraints, the validity measure evaluates the degree of data meeting the constraints, e.g., whether the values are in the specified range or fluctuate drastically over time in a series. It is worth noting that simply counting all the data points in violation to the constraints may over claim the data validity issue. Following the minimum change criteria in data repairing, we propose to study the minimum number of data points that need to be changed in order to satisfy the constraints, or equivalently, the maximum rate of data that can be reserved without change, as the validity measure. To our best knowledge, this is the first study on defining and evaluating time series data validity. We devise algorithms for computing the validity measure in quadratic time and linear space. Remarkably, the validity measure has been deployed and included as a function in SQL statements, in Apache IoTDB, an open-source time series database. The algorithm fully adapts to the LSM-based storage of time series in multiple segments. Extensive experiments over 8 real-world datasets show up to 4 orders of magnitude improvement in time cost compared to the related method SCREEN.