In a stream environment, di
fferently
from traditional databases, data arrive
continuously, unindexed and potentially unbounded, whereas queries must be evaluated
for producing results on the
fly. In this article, we propose two new algorithms (called SLCAStream and ELCAStream)
for processing multiple keyword queries over XML streams. Both algorithms process keyword-based queries that require minimal or no schema knowledge to be
formulated,
follow the lowest common ancestor (LCA) semantics, and provide optimized methods to improve the overall per
formance. Moreover, SLCAStream, which implements the smallest LCA (SLCA) semantics, outper
forms the state-o
f-the-art, with up to 49% reduction in response time and 36% in memory usage. In turn, ELCAStream is the
first to explore the exclusive LCA (ELCA) semantics over XML streams.
A comprehensive set of experiments evaluates several aspects related to performance and scalability of both algorithms, which shows they are effective alternatives to search services over XML streams.