CoUPE: Continuous Query Processing Engine for Evolving Graphs

Continuously Evolving Graphs (CEGs) are graphs whose connectivity constantly changes over time is uniquely important for many domains such as social networks, evolutionary genomics, communication networks etc. In many of these it is often important to keep track of connectivity among the nodes of interest as the underlying structure changes over time. While interval-based indexing has been a popular strategy for testing reachability in static graphs, it cannot be directly applied in the context of evolving graphs. In this paper, we propose CoUPE (Continuous qUery Processing Engine), which, to our best knowledge, is the first time-efficient framework for answering continuous reachability queries in evolving graphs. The main idea here is to maintain the indices of the evolving graph and recalculate only a subset of reachability queries using a novel heuristic to determine the change in the state of queries because for the most recent change in the graph. We make three novel contributions while designing CoUPE. First, we introduce a generic indexing and querying framework for answering continuous queries in large time-evolving graphs. Second, we design a highly efficient, scalable and provably correct algorithm for updating the indices of graph by analyzing the changes happening on the graph. Third, we present a novel heuristic-based technique for identifying which subset of existing queries might get effected because of the most recent edit. This paper also presents a detailed experimental study demonstrating the scalability and efficiency of the processing engine.