Using Semi-Joins to Solve Relational Queries

Abstract

The semi-join is a relational algebraic operation that selects a set of tuples in one relation that match one or more tuples of another relation on the joining domains. Semi-joins have been used as a basic ingredient in query processing strategies for a number of hardware and software database systems. However, not all queries can be solved entirely using semi-joins. In this paper the exact class of relational queries that can be solved using semi-joins is shown. It is also shown that queries outside of this class may not even be partially solvable using "short" semi-join programs. In addition, a linear-time membership test for this class is presented.KEY WORDS AND PHRASES: semi-join, relational database, relational query processing cR CATEGORIES: 3.74, 4.33, 5.25

gStore: a graph-based SPARQL query engine

“…E = { − −− → u 1 , u 2 } is a collection of directed edges that connect the corresponding subjects and objects. 4. L E is a collection of edge labels.…”

“…In order to speed up query processing, we do not materialize all summary matches in non-leaf levels. Instead, we apply a semijoin [4] like pruning strategy, i.e., pruning some nodes (in the VS * -tree) that are not possible in any summary match, and incorporate it into VS * -query algorithm.…”

Evaluation of Join Strategies for Distributed Mediation

“…1 1 . It improves the naive strategy by the following two data transformations based on the semi-join algorithm [2]:…”

“…The traditional semi-join algorithm (SJA) [2] improves the performance of the PCA when duplicates are involved. After projecting the input bulk over the columns used as input to the remote query fragment, SJA performs duplicate removal before shipping the data.…”

“…This type of implementation leads to considerably different results where the ship-out method always outperforms ship-in. Disk-based semi-join algorithms are described in [1,2,5,14]. A sort-merge join, bloom filter semi-join, and sort-based semi-join are evaluated in [15] for a distributed database environment.…”