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We investigate the enumeration of query results for an important subset ofCQs with projections, namely star and path queries. The task is to design datastructures and algorithms that allow for efficient enumeration with delayguarantees after a preprocessing phase. Our main contribution is a series ofresults based on the idea of interleaving precomputed output with further joinprocessing to maintain delay guarantees, which maybe of independent interest.In particular, for star queries, we design combinatorial algorithms thatprovide instance-specific delay guarantees in linear preprocessing time. Thesealgorithms improve upon the currently best known results. Further, we show howexisting results can be improved upon by using fast matrix multiplication. Wealso present new results involving tradeoff between preprocessing time anddelay guarantees for enumeration of path queries that contain projections.Boolean matrix multiplication is an important query that can be expressed as aCQ with projection where the join attribute is projected away. Our results cantherefore also be interpreted as sparse, output-sensitive matrix multiplicationwith delay guarantees.

Enumeration Algorithms for Conjunctive Queries with Projection