•Can’t go directly to S3 because it requires a
binding.
•Can go to S1, get UW papers, and check if they’re in
S3.
•Can go to S1, get UW
papers, feed them into S2, and feed the
results into S3.
•Can go to S1, feed results into S2, feed results into S2
again, and then feed
results into S3.
•Strictly speaking, we can’t a priori decide when to
stop.
•Need recursive
query processing.