DOAS: A Drought Online Analysis System with Constraint Databases

The Standardized Precipitation Index (SPI) [5] is a common and simple measure of the intensity and duration of drought at certain measured point locations. We interpolate this original point-based SPI data using a shape function-based interpolation [3], which is the most accurate among a number of alternatives [2], and represent the result in a constraint database [1, 6]. A drought event occurs any time the SPI is continuously negative and reaches an intensity of −1 or less, and it ends when the SPI becomes positive [5]. This recursive definition is difficult for most database systems to implement and visualize. The Drought Online Analysis System (DOAS) uses a constraint database to represent the spatio-temporal data and allows both SQL and recursive, namely Datalog, queries which are high-level and easy to maintain. DOAS is a server-based and three-tier spatio-temporal system and supports animation of spatio-temporal results.