# Hypothetical answers to continuous queries over data streams

## TL;DR

This paper introduces a semantics and online algorithm for continuous data stream queries that provide hypothetical answers, enabling users to consider possible future states despite delays or blocking in data processing.

## Contribution

It proposes a novel semantics for hypothetical answers in continuous queries and an online method to update consistent facts based on current information.

## Key findings

- Provides a formal semantics for hypothetical answers
- Develops an online algorithm for fact updating
- Enables real-time consideration of possible future data states

## Abstract

Continuous queries over data streams may suffer from blocking operations and/or unbound wait, which may delay answers until some relevant input arrives through the data stream. These delays may turn answers, when they arrive, obsolete to users who sometimes have to make decisions with no help whatsoever. Therefore, it can be useful to provide hypothetical answers - "given the current information, it is possible that X will become true at time t" - instead of no information at all. In this paper we present a semantics for queries and corresponding answers that covers such hypothetical answers, together with an online algorithm for updating the set of facts that are consistent with the currently available information.