Progressive Approximate Aggregation

Definition

Aggregate queries are answered by computing a single scalar value over a set of relevant data objects, e.g., the average temperature over all sensors in a region of space. Often, the precise value is not needed because the user may not be interested in knowing the temperature to the last decimal point. Additionally, the mode of visualization of the answer, e.g., in a virtual navigation, may in itself impose restrictions by necessitating either a high frame rate or the color-coding of the answer at a specific resolution. Progressive approximate aggregate queries compute the answer progressively, coming up with an initial estimate and refining it until the time deadline (e.g., time to render the frame), or answer quality precision (e.g., ±1 ^∘C) is reached. Thus, they are a flexible way of query processing since they make no assumptions about the time/accuracy specifications imposed by the user application and can accommodate a wide variety of such specifications in a unified...