On the Memory Requirements of XPath Evaluation over XML Streams

The important challenge of evaluating XPath queries over XML streams has sparked much interest in the past few years. A number of algorithms have been proposed, supporting wider fragments of the query language, and exhibiting better performance and memory utilization. Nevertheless, all the algorithms known to date use a prohibitively large amount of memory for certain types of queries. A natural question then is whether this memory bottleneck is inherent or just an artifact of the proposed algorithms. In this paper we initiate the first systematic and theoretical study of lower bounds on the amount of memory required to evaluate XPath queries over XML streams. We present a general lower bound technique, which given a query, specifies the minimum amount of memory that any algorithm evaluating the query on a stream would need to incur. The lower bounds are stated in terms of new graph-theoretic properties of queries. The proofs are based on tools from communication complexity. We then e...

• Type: Conference
• Year: 2004
• Where: PODS
• Authors: Ziv Bar-Yossef, Marcus Fontoura, Vanja Josifovski
• Keywords: Database, Lower Bound Technique, Lower Bounds, PODS 2004, XPATH Queries